Using NSwag to Generate Blazor Server Client for an ASP.NET Core 3.1 API

This week we are going to add a Blazor Server project that will utilize the contacts API we created a few weeks ago. This post is part of the revamp of the ASP.NET Core Basics repo that was kicked off when .NET Core 3.0 was released. For details on how the associated sample got to the current point in the application check out the following posts.

Swagger/OpenAPI with NSwag and ASP.NET Core 3
ASP.NET Core 3: Add Entity Framework Core to Existing Project
New Razor Pages Project Backed with an API
Using NSwag to Generate Angular Client for an ASP.NET Core 3 API
Using NSwag to Generate React Client for an ASP.NET Core 3 API

The sample code before any of the changes in this post can be found here.

Create the Blazor Server Project

Add a new directory for the Blazor Server project and then open a terminal set to that directory. The following command can be used to create a new Blazor Server project.

dotnet new blazorserver

Next, use the following command to add the new project to the solution file which is in the root of the repo. Your filenames and paths will vary of course.

dotnet sln ..\..\BasicsRefresh.sln add ContactsBlazorServerApp.csproj

Using NSwageStudio to Generate an API Client

NSwag provides multiple options for client generation including a CLI option, code, and a Windows application. This post is going to use the Windows application which is called NSwagStudio. Download and install NSwagStudio from here.

Next, make sure your API is running and get the URL of its OpenAPI/Swagger specification URL. For example, I am using a local instance of my API and the URL I need is https://localhost:5001/swagger/v1/swagger.json. If you are using the Swagger UI you can find a link to your swagger.json under the API title.

Now that we have the OpenAPI/Swager specification URL for the API switch over to NSwagStudio. The application will open with a new document ready to go. There are a few options we will need to set. First, we want to use the NetCore30 Runtime. Next, select the OpenAPI/Swagger Specification tab and enter your API’s specification URL in the Specification URL box.

In the Outputs section check the CSharp Client checkbox and then select the CSharp Client tab. For this example, we are taking the defaults for all of the options except for Namespace, which is set to ContactsApi, Generate interfaces for Client classes, which should be check, and Output file path, which is only needed if you use the Generate Files option. Click the Generate Files button and NSwagStudio will create a file that contains all the code needed to access the API described in the OpenAPI/Swager specification selected in the Input section.

The Generate Outputs button can be used if to populate the Output tab with the same code that the Generate Files process creates which provides a nice way to play with settings to and see the output without having to open another file.

Setting Up the Generated Client in the Blazor Server Project

In the sample project, create an APIs directory and dropped the ContactsApi.cs created with NSwagStudio there. The files generated with NSwagStudio are expecting JSON.NET to be present so the sample project will need a reference to the Microsoft.AspNetCore.Mvc.NewtonsoftJson NuGet package.

With the client-generated and in our local Apis directory in the Razor Pages project we can now work on getting it configured and registered for use in our new project. First, open the apppsetting.json file and add a setting for the URL of our API, which is the ContactsApi value in the following sample.

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*",
  "ContactsApi": "https://localhost:5001"
}

Now that the project has the configuration change and a reference to JSON.NET in the ConfigureServices function of the Startup class we need to tell the app to make JSON.NET available via dependency injection by using AddNewtonsoftJson as in the following example.

services.AddRazorPages()
        .AddNewtonsoftJson();

Also in the ConfigureServices function, we need to register our API client.

services.AddHttpClient<IContactsClient, 
                       ContactsClient>(client => 
         client.BaseAddress = new Uri(Configuration.GetSection("ContactsApi").Value));

Create the UI and Usage of the Generated Client

Now that all the setup work is done we can add the contact list UI which will show the usage of the API client. The following is the full code which for the sample is in a new ContactList.razor file in the Pages directory. The specific lines related to the API client are highlighted.

@page "/contactlist"

@using Apis
@inject IContactsClient ContactClient

<h1>Contact List</h1>

@if (_contacts == null)
{
    <p><em>Loading...</em></p>
}
else
{
    <table className='table table-striped' aria-labelledby="tabelLabel">
        <thead>
            <tr>
                <th>Name</th>
                <th>Address</th>
                <th>City</th>
                <th>State</th>
                <th>Postal Code</th>
                <th>Phone</th>
                <th>Email</th>
            </tr>
        </thead>
        <tbody>
            @foreach (var contact in _contacts)
            {
                <tr>
                    <td>@contact.Name</td>
                    <td>@contact.Address</td>
                    <td>@contact.City</td>
                    <td>@contact.State</td>
                    <td>@contact.PostalCode</td>
                    <td>@contact.Phone</td>
                    <td>@contact.Email</td>
                </tr>
            }
        </tbody>
    </table>
}

@code {
    private ICollection<Contact> _contacts;

    protected override async Task OnInitializedAsync()
    {
        _contacts = await ContactClient.GetContactsAsync();
    }
}

Finally to add our new page to the navbar open the NavMenu.razor file found in the Shared directory. Add the following list item to the unordered list.

<li class="nav-item px-3">
    <NavLink class="nav-link" href="contactlist">
        <span class="oi oi-list" aria-hidden="true"></span> Contacts
    </NavLink>
</li>

Wrapping Up

As with the other posts I have been doing utilizing NSwag for client generation this process is pretty easy and simplifies API consumption.

The sample code in its final state can be found here.

Migration from ASP.NET Core 3.0 to 3.1

On December 3rd .NET Core 3.1 was released which included a new release of ASP.NET Core 3.1 and Entity Framework Core 3.1. This post is going to walk through updating the Contacts API project from the refreshed ASP.NET Basics series. All the changes I made came from Microsoft’s Migrate from ASP.NET Core 3.0 to 3.1 doc.

The code before any changes can be found here.

Installation

If you are a Visual Studio user you can get .NET Core 3.0 by installing at least Visual Studio 16.4. For those not using Visual Studio, you can download and install .NET Core 3.1 SDK from here. As with previous versions, the SDK is available for Windows, Linux, and Mac.

After installation is complete you can run the following command from a command prompt to see all the versions of the .NET Core SDK you have installed.

dotnet --list-sdks

You should see 3.1.100 listed at a minimum.

Project File Changes

Right-click on the project and select Edit projectName.csproj.

Change the TargetFramework to netcoreapp3.1.

Before:
<TargetFramework>netcoreapp3.0</TargetFramework>

After
<TargetFramework>netcoreapp3.1</TargetFramework>

Next, update all your packages to the new versions. This is going to vary greatly based on your project. This can be done manually in the csproj file or via the NuGet UI if you are using Visual Studio. The following are the changes from the sample project.

Before:
<PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="3.0.0">
<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="3.0.0" />
<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="3.0.0" />
<PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="3.0.0">
<PackageReference Include="Microsoft.Extensions.Logging.Debug" Version="3.0.0" />
<PackageReference Include="Microsoft.IO.RecyclableMemoryStream" Version="1.2.0" />
<PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="3.0.0" />
<PackageReference Include="NSwag.AspNetCore" Version="13.1.3" />

After:
<PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="3.1.0">
<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="3.1.0" />
<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="3.1.0" />
<PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="3.1.0">
<PackageReference Include="Microsoft.Extensions.Logging.Debug" Version="3.1.0" />
<PackageReference Include="Microsoft.IO.RecyclableMemoryStream" Version="1.3.2" />
<PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="3.1.0" />
<PackageReference Include="NSwag.AspNetCore" Version="13.1.6" />

Wrapping Up

The move from 3.0 to 3.1 is drop-dead simple which is not surprising since it has only been a few months since the release of 3.0. It is important to move to 3.1 as soon as you can since it is the long term service version and will be supported for at least the next 3 years where 3.0 will lose support within months.

Log Requests and Responses in ASP.NET Core 3

This post is going to be a refresh of the Log Requests and Responses in ASP.NET Core post which no longer works more modern versions of ASP.NET Core. For the most part, this post will exactly match the original but with the code bits updated.

As part of trying to do some debugging, I needed a way to log the requests and responses. Writing a piece of middleware seemed to be a good way to handle this problem. It also turned out to be more complicated than I had expected to deal with the request and response bodies.

Middleware

In ASP.NET Core middleware are the components that make up the HTTP pipeline that handles requests and responses for the application. Each piece of middleware called has the option to do some processing on the request before calling the next piece of middleware in line. After execution returns from the call to the next middleware, there is an opportunity to do processing on the response.

The HTTP pipeline for an application is set in the Configure function of the Startup class. Run, Map and Use are the three types of middleware available. Run should only be used to terminate the pipeline. Map is used for pipeline branching. Use seems to be the most common type of middleware that does some processing and call the next middleware in line. For more detail see the official docs.

Creating Middleware

Middleware can be implemented as a lambda directly in the Configure function, but more typically it is implemented as a class that is added to the pipeline using an extension method on IApplicationBuilder. This example will be using the class route.

This example is a piece of middleware that uses ASP.NET Core’s built-in logging to log requests and responses. Create a class called RequestResponseLoggingMiddleware.

The class will need a constructor that takes two arguments both will be provided by ASP.NET Core’s dependency injection system. The first is a RequestDelegate which will be the next piece of middleware in the pipeline. The second is an instance of an ILoggerFactory which will be used to create a logger. The RequestDelegate is stored to the class level _next variable and the loggerFactory is used to create a logger that is stored to the class level _logger variable.

public class RequestResponseLoggingMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger _logger;

    public RequestResponseLoggingMiddleware(RequestDelegate next,
                                            ILoggerFactory loggerFactory)
    {
        _next = next;
        _logger = loggerFactory
                  .CreateLogger<RequestResponseLoggingMiddleware>();
    }
}

Add an Invoke function which is the function that will be called when your middleware is run by the pipeline. The following is the function that does nothing other than call the next middleware in the pipeline.

public async Task Invoke(HttpContext context)
{
     //code dealing with the request

     await _next(context);

     //code dealing with the response
}

Next, add a static class to simplify adding the middleware to the application’s pipeline. This is the same pattern the built-in middleware uses.

public static class RequestResponseLoggingMiddlewareExtensions
{
    public static IApplicationBuilder UseRequestResponseLogging(this IApplicationBuilder builder)
    {
        return builder.UseMiddleware<RequestResponseLoggingMiddleware>();
    }
}

Adding to the pipeline

To add the new middleware to the pipeline open the Startup.cs file and add the following line to the Configure function.

app.UseRequestResponseLogging();

Keep in mind that the order in which middleware is added can make a difference in how the application behaves. Since the middleware this post is dealing with is logging I have placed it near the start of the pipeline.

Logging requests and responses

Now that the setup work for our new middleware is done we will come back to its Invoke function. As I stated above this ended up being more complicated than I expected, but thankfully I found this by Sul Aga which really helped me work through the issues I was having along with a lot of feedback on the original version of this post.

One of the bits of feedback on the original version of this post was about a potential memory leak and using recyclable memory streams. First, add a NuGet reference to the Microsoft.IO.RecyclableMemoryStream package. Next, we will add a class-level variable to hold an instance of a RecyclableMemoryStreamManager which we will create in the constructor. The following is an updated class view with these changes as well as changes to the Invoke function and stubs for the logging methods.

public class RequestResponseLoggingMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger _logger;
    private readonly RecyclableMemoryStreamManager _recyclableMemoryStreamManager;

    public RequestResponseLoggingMiddleware(RequestDelegate next,
                                            ILoggerFactory loggerFactory)
    {
        _next = next;
        _logger = loggerFactory
                  .CreateLogger<RequestResponseLoggingMiddleware>();
        _recyclableMemoryStreamManager = new RecyclableMemoryStreamManager();
    }

    public async Task Invoke(HttpContext context)
    {
        await LogRequest(context);
        await LogResponse(context);
    }
  
    private async Task LogRequest(HttpContext context) {}
    private async Task LogResponse(HttpContext context) {}
}

First, we are going to look at the LogRequest function, and a helper function it uses.

private async Task LogRequest(HttpContext context)
{
    context.Request.EnableBuffering();

    await using var requestStream = _recyclableMemoryStreamManager.GetStream();
    await context.Request.Body.CopyToAsync(requestStream);
    _logger.LogInformation($"Http Request Information:{Environment.NewLine}" +
                           $"Schema:{context.Request.Scheme} " +
                           $"Host: {context.Request.Host} " +
                           $"Path: {context.Request.Path} " +
                           $"QueryString: {context.Request.QueryString} " +
                           $"Request Body: {ReadStreamInChunks(requestStream)}");
    context.Request.Body.Position = 0;
}

private static string ReadStreamInChunks(Stream stream)
{
    const int readChunkBufferLength = 4096;

    stream.Seek(0, SeekOrigin.Begin);

    using var textWriter = new StringWriter();
    using var reader = new StreamReader(stream);

    var readChunk = new char[readChunkBufferLength];
    int readChunkLength;

    do
    {
        readChunkLength = reader.ReadBlock(readChunk, 
                                           0, 
                                           readChunkBufferLength);
        textWriter.Write(readChunk, 0, readChunkLength);
    } while (readChunkLength > 0);

    return textWriter.ToString();
}

The key to getting this function to work and allow reading of the request body was context.Request.EnableBuffering() which allows us to read from the beginning of the stream. The rest of the function is pretty straight forward.

The next function is LogResponse which is used to execute the next bit of middleware in the pipeline, using await _next(context) and then logging the response body after the rest of the pipeline has run.

private async Task LogResponse(HttpContext context)
{
    var originalBodyStream = context.Response.Body;

    await using var responseBody = _recyclableMemoryStreamManager.GetStream();
    context.Response.Body = responseBody;

    await _next(context);

    context.Response.Body.Seek(0, SeekOrigin.Begin);
    var text = await new StreamReader(context.Response.Body).ReadToEndAsync();
    context.Response.Body.Seek(0, SeekOrigin.Begin);

    _logger.LogInformation($"Http Response Information:{Environment.NewLine}" +
                           $"Schema:{context.Request.Scheme} " +
                           $"Host: {context.Request.Host} " +
                           $"Path: {context.Request.Path} " +
                           $"QueryString: {context.Request.QueryString} " +
                           $"Response Body: {text}");

    await responseBody.CopyToAsync(originalBodyStream);
}

As you can see the trick to reading the response body is replacing the stream being used with a new MemoryStream and then copying the data back to the original body steam. I don’t know how much this affects performance and would make sure to study how it scales before using it in a production environment.

Wrapping up

I hope this updated post turns out to be as helpful as the original seemed to be. This round I do have the code in a GitHub repo and the commit with the related changes can be found here.

Using NSwag to Generate React Client for an ASP.NET Core 3 API

This week we are going to add a React project that will utilize the contacts API we created a few weeks ago. This post is part of the revamp of the ASP.NET Core Basics repo that was kicked off when .NET Core 3.0 was released. For details on how the associated sample got to the current point in the application check out the following posts.

Swagger/OpenAPI with NSwag and ASP.NET Core 3
ASP.NET Core 3: Add Entity Framework Core to Existing Project
New Razor Pages Project Backed with an API
Using NSwag to Generate Angular Client for an ASP.NET Core 3 API

I realize that using an ASP.NET Core backed React project for this sample is overkill and a raw React application would have been all that is needed. I chose to use the ASP.NET Core template as a base for all the projects in this series to be consistent. After the initial application creation, you can think of this example as setting up access to a secondary API in addition to the application’s main API if that helps or the generated client on the React side could be used to wrap the API generated by the template.

The sample code before any of the changes in this post can be found here.

Create the React Project

Add a new directory for the React project and then open a terminal set to that directory. The following command can be used to create a new React project. The target framework isn’t required, but I have a preview of .NET Core 3.1 installed and I wanted to make sure this project is targeting .NET Core 3.0.

dotnet new react -f netcoreapp3.0

Next, use the following command to add the new project to the solution file which is in the root of the repo. Your filenames and paths will vary if you are not using the sample code of course.

dotnet sln ..\..\BasicsRefresh.sln add ContactsReact.csproj

Use NSwagStudio to Generate React Client

NSwag provides multiple options for client generation including a CLI, code, and a Windows application. This post is going to use the Windows application which is called NSwagStudio. Download and install NSwagStudio from here.

Next, make sure your API is running and get the URL of its OpenAPI/Swagger specification URL. For example, I am using a local instance of my API and the URL I need is https://localhost:5001/swagger/v1/swagger.json. If you are using the Swagger UI you can find a link to your swagger.json under the API title.

Now that we have the OpenAPI/Swager specification URL for the API switch over to NSwagStudio. The application will open with a new document ready to go. There are a few options we will need to set. First, select the OpenAPI/Swagger Specification tab and enter your API’s specification URL in the Specification URL box.

In the Outputs section check the TypeScript Client checkbox and then select the TypeScript Client tab. There are a lot of options to play with, but I highlighted the options that were important for this sample. First, make sure Module name and Namespace are both empty. I’m sure there is a way to get the client working with a module or namespace, but I didn’t have any luck.   For Template, we just need a Fetch based client. The final option that needs to be set is the Output file path and this is the location you want the generated file to be. I output to the React project directory under ClientApp\src\app\components\contactApi.ts. After all the options are set click Generate Files.

Create UI and Use Generated Client

Once the above is done once you switch back to Visual Studio you should see the following prompt to add the Microsoft.TypeScript.MSBuild NuGet package. The React template doesn’t use TypeScript and NSwag doesn’t have an option to generate a plain JavaScript client so adding this package will allow the build process to take our TypeScript client and convert it to JavaScript. There is an open issue requesting a JavaScript generator.

The sample API is for contact management so the UI we are going to build is to display a contact list. In the ClientApp/src/component directory add a new file named ContactList.js with the following contents. The lines specific to the usage of the NSwag generated client are highlighted.

import React, { Component } from 'react';
import { ContactsClient } from './contactsApi';  

export class ContactList extends Component {
    static displayName = ContactList.name;

    constructor(props) {
        super(props);
        this.state = { contacts: [], loading: true };
    }

    componentDidMount() {
        this.populateContactData();
    }

    static renderContactsTable(contacts) {
        return (
            <table className='table table-striped' aria-labelledby="tabelLabel">
                <thead>
                    <tr>
                        <th>Name</th>
                        <th>Address</th>
                        <th>City</th>
                        <th>State</th>
                        <th>Postal Code</th>
                        <th>Phone</th>
                        <th>Email</th>
                    </tr>
                </thead>
                <tbody>
                    {contacts.map(contact =>
                        <tr key={contact.id}>
                            <td>{contact.name}</td>
                            <td>{contact.address}</td>
                            <td>{contact.city}</td>
                            <td>{contact.state}</td>
                            <td>{contact.postalCode}</td>
                            <td>{contact.phone}</td>
                            <td>{contact.email}</td>
                        </tr>
                    )}
                </tbody>
            </table>
        );
    }

    render() {
        let contents = this.state.loading
            ? <p><em>Loading...</em></p>
            : ContactList.renderContactsTable(this.state.contacts);

        return (
            <div>
                <h1 id="tabelLabel" >Contacts</h1>
                {contents}
            </div>
        );
    }

    async populateContactData() {
        let client = new ContactsClient();
        client.getContacts()
              .then(data => this.setState({ contacts: data, loading: false }));
    }
}

As you can see from the populateContactData code above we are creating a new instance of the ContactsClient and calling its getContacts function and using the data we get back from the API to set the state of the component with the data return from the API.

Now that the contact list is ready it needs a link in the navbar. First, in the App.js file, we need to add the contact list to the router. The following is the full file with the added lines highlighted.

import React, { Component } from 'react';
import { Route } from 'react-router';
import { Layout } from './components/Layout';
import { Home } from './components/Home';
import { FetchData } from './components/FetchData';
import { Counter } from './components/Counter';
import { ContactList } from './components/ContactList';

import './custom.css'

export default class App extends Component {
  static displayName = App.name;

  render () {
    return (
      <Layout>
        <Route exact path='/' component={Home} />
        <Route path='/contacts' component={ContactList} />
        <Route path='/counter' component={Counter} />
        <Route path='/fetch-data' component={FetchData} />
      </Layout>
    );
  }
}

Now to make to add a Contacts link to the navbar open the NavMenu.js file and add the following to the with the other nav items.

<NavItem>
    <NavLink tag={Link} className="text-dark" to="/contacts">Contacts</NavLink>
</NavItem>

Wrapping  Up

I had a bit more trouble getting the NSwag client working this round, but that was more due to my shallow knowledge with React than a problem with NSwag.

The sample projects after all the changes in this post can be found here.

Using NSwag to Generate Angular Client for an ASP.NET Core 3 API

This week we are going to add an Angular project that will utilize the API we created a few weeks ago. This post is part of the revamp of my ASP.NET Core Basics repo that I kicked off when .NET Core 3.0 was released. For details on how we got to the current point in the application check out the following posts.

Swagger/OpenAPI with NSwag and ASP.NET Core 3
ASP.NET Core 3: Add Entity Framework Core to Existing Project
New Razor Pages Project Backed with an API

Do note that I realize that using an ASP.NET Core backed Angular project for this sample is overkill and a plain Angular application would have been all that is needed, but I wanted to use the ASP.NET Core template as a base for all the projects in this series. After the initial application creation, you can think of this example as setting up access to a secondary API in addition to the application’s main API if that helps.

The sample code before any of the changes in this post can be found here.

API Changes

Before we get to the actual Angular side of this post we are going to update the associated API to accept all cross-origin resource sharing (CORS) requests. The ASP.NET Core setup has a lot of options and I recommend being me explicit about what your API will accept if you can. Check out the official Microsoft CORS docs for more information.

All the changes needed will be in the Startup class of the API project. The CORS setup is policy-based and each policy needs a name that I stored in the following class level constant.

private const string AllowAllCors = "AllowAll";

In the ConfigureServices function add the following to register the CORS policy. Again be more restrictive with your policy if you can but for this example, we are opening up the API to allow any request.

services.AddCors(options =>
                 {
                     options.AddPolicy(AllowAllCors,
                                       builder =>
                                       {
                                           builder.AllowAnyHeader();
                                           builder.AllowAnyMethod();
                                           builder.AllowAnyOrigin();
                                       });
                 });

Finally, in the Configure function add the following to get CORS added to the HTTP pipeline processing. I’m not 100% sure if it matters where you added it in the pipeline, but I added it close to the front. I included a bit pipeline in the sample app for reference.

if (env.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
}

app.UseCors(AllowAllCors);

app.UseHttpsRedirection();

That is all the changes needed for the API, next we will create a new Angular project.

Create an Angular Project

Add a new directory for the application and then in a terminal navigate to that directory. Then the following command can be used to create the new Angular project. The target framework isn’t required, but I have a preview of .NET Core 3.1 installed and I wanted to make sure this project is targeting .NET Core 3.0.

dotnet new angular -f netcoreapp3.0

Next, use the following command to add the new project to the solution file which is in the root of the repo. Your filenames and paths could vary if you can’t using the same code of course.

dotnet sln ..\..\BasicsRefresh.sln add ContactsAngular.csproj

Use NSwagStudio to Generate Angular Client

NSwag provides multiple options for client generation including a CLI option, code, and a Windows application. This post is going to use the Windows application which is called NSwagStudio. Download and install NSwagStudio from here.

Next, make sure your API is running and get the URL of its OpenAPI/Swagger specification URL. For example, I am using a local instance of my API and the URL I need is https://localhost:5001/swagger/v1/swagger.json. If you are using the Swagger UI you can find a link to your swagger.json under the API title.

Now that we have the OpenAPI/Swager specification URL for the API switch over to NSwagStudio. The application will open with a new document ready to go. There are a few options we will need to set. First, select the OpenAPI/Swagger Specification tab and enter your API’s specification URL in the Specification URL box.

In the Outputs section check the TypeScript Client checkbox and then select the TypeScript Client tab. There are a lot of options to play with, but I highlighted the ones I changed to generate the client for this sample. First I entered a Module name so the generated code will all be in that module. For Template, it is very important to select Angular so that the resulting code will be set up for Angular’s dependency injection. Also, make sure and change the Injection token type to InjectionToken if you are on a newer version of Angular. The final option that needs to be set is the Output file path and this is the location you want the generated file to be. I output the Angular project directory under ClientApp\src\app\apis\contactApi.ts. After all the options are set click Generate Files.

For more information on generating Angular clients check the official docs on the subject.

Create UI and Use Generated Client

The sample API is for contact management so the UI we are going to build is to display a contact list. The new components are going to go in a new contacts directory under ClientApp\src\app. In this directory, we will need two new files one for the HTML, contact-list.component.html, and the other for the backing TypeScript class, contact-list.component.ts.

The following is the full content on the HTML file. I’m not going to go into the Angular specific bit in this post, but even if you don’t know Angular you will get the idea of what is going on. The rendered result will be a table of contacts.

<h1 id="tableLabel">Contacts</h1>

<p *ngIf="!contacts"><em>Loading...</em></p>

<table class='table table-striped' aria-labelledby="tableLabel" *ngIf="contacts">
  <thead>
    <tr>
      <th>Name</th>
      <th>Address</th>
      <th>City</th>
      <th>State</th>
      <th>Postal Code</th>
      <th>Phone</th>
      <th>Email</th>
    </tr>
  </thead>
  <tbody>
    <tr *ngFor="let contact of contacts">
      <td>{{ contact.name }}</td>
      <td>{{ contact.address }}</td>
      <td>{{ contact.city }}</td>
      <td>{{ contact.state }}</td>
      <td>{{ contact.postalCode }}</td>
      <td>{{ contact.phone }}</td>
      <td>{{ contact.email }}</td>
    </tr>
  </tbody>
</table>

Next is the TypeScript class for the contact list. This is where you get to see the usage of the client that NSwag generated. The related lines are highlighted.

import { Component } from '@angular/core';
import { contacts as Contacts } from "../apis/contactApi";

@Component({
  selector: 'app-contact-list',
  templateUrl: './contact-list.component.html'
})
export class ContactListComponent {
  public contacts: Contacts.IContact[];

  constructor(contactsClient : Contacts.ContactsClient) {
    contactsClient.getContacts().subscribe(result => {
        this.contacts = result;
      },
      error => console.error(error));
  }
}

As you can see from the code above we are injecting the ContactClient and then calling its getContracts and assigning the results to the class’s local contacts variable.

Now that our components are built we need to register them with the application. These changes are in the app.module.ts file found in the ClientApp\src\app directory. The following is the full file excluding the imports that were existing with the changes for our contact related items highlighted.

import { ContactListComponent } from "./contacts/contact-list.component";
import { contacts } from "./apis/contactApi";

@NgModule({
  declarations: [
    AppComponent,
    NavMenuComponent,
    HomeComponent,
    CounterComponent,
    FetchDataComponent,
    ContactListComponent
  ],
  imports: [
    BrowserModule.withServerTransition({ appId: 'ng-cli-universal' }),
    HttpClientModule,
    FormsModule, 
    RouterModule.forRoot([
      { path: '', component: HomeComponent, pathMatch: 'full' },
      { path: 'contact-list', component: ContactListComponent },
      { path: 'counter', component: CounterComponent },
      { path: 'fetch-data', component: FetchDataComponent },
    ])
  ],
  providers: [contacts.ContactsClient],
  bootstrap: [AppComponent]
})
export class AppModule { }

The first change was to import both the ContactListComponent and contacts which is the contact client. Next, the ContactListComponent was added to the declarations array. Then we added the ContactListComponent to the RouterModule so that Angular will know how to get us to the contact list page. Finally, we added the ContractsClient to the providers array which will allow Angular to inject the client into our contact list component.

To add our contact list to the nav menu we need to change the nav-menu.component.html file in the ClientApp\src\app\nav-menu directory. Add the following list item to add a Contact link in the navbar.

<li class="nav-item" [routerLinkActive]="['link-active']">
  <a class="nav-link text-dark" [routerLink]="['/contact-list']"
    >Contacts</a
  >
</li>

Wrapping Up

I’m repeating myself, but NSwag’s client generation makes it very simple to get starting consuming APIs, but even over time being able to regenerate a client for an API and have any changes in that API ready to go is really nice.

The sample projects after all the changes in this post can be found here.

ASP.NET Core: An attempt was made to access a socket in a way forbidden by its access permissions

This morning I made some changes to a project for a future post. Minor stuff and nothing that should have caused issues, but when I tried to run the project I got the following error from Kestrel.

warn: Microsoft.AspNetCore.Server.Kestrel[0]
Unable to bind to https://localhost:5001 on the IPv4 loopback interface: ‘An attempt was made to access a socket in a way forbidden by its access permissions.’.
warn: Microsoft.AspNetCore.Server.Kestrel[0]
Unable to bind to https://localhost:5001 on the IPv6 loopback interface: ‘An attempt was made to access a socket in a way forbidden by its access permissions.’.
crit: Microsoft.AspNetCore.Server.Kestrel[0]
Unable to start Kestrel.
System.IO.IOException: Failed to bind to address https://localhost:5001.

I had limited time so I switched the project over to launch using IIS Express and hit run, but this resulted in the following error.

HTTP Error 500.35 – ANCM Multiple In-Process Applications in same Process

Switching back to Kestrel and changing the port number in the applicationUrl setting in the launchSettings.json file fixed the issue. Later I came back to the application and tried to track down what was using the same ports and couldn’t find anything. After a reboot, all worked fine with Kestrel and the original port numbers.

For the IIS Express error, I ended up having to delete the .vs directory which can be found in the same directory as your solution file if you are using Visual Studio 2019. Thanks to stackoverflow for this fix.

Wrapping Up

Not the post I set out to write this week, but hopefully this will save someone some searching in the future, more than likely myself.

New Razor Pages Project Backed with an API

This week we are going to add a Razor Pages project that will utilize the API we created a few weeks ago. This post is part of the revamp of my ASP.NET Core Basics repo that I kicked off when .NET Core 3.0 was released. For details on how we got to the current point in the application check out the following posts.

Swagger/OpenAPI with NSwag and ASP.NET Core 3
ASP.NET Core 3: Add Entity Framework Core to Existing Project

The code before the changes in this post can be found in this GitHub repo.

Razor Pages Project

Add a new directory for the application and then in a terminal navigate to that directory. Then the following command can be used to create the new Razor Pages application.

dotnet new webapp

Next, use the  following command to add the new project to the solution file which is in the root of the repo. Your filenames and paths could vary if you can’t using the same code of course.

dotnet sln ..\..\BasicsRefresh.sln add ContactsRazorPages.csproj

API Access Setup

For API access we are using NSwag to generate a client that our Razor Page application will use. For the actual creation of the API client see the following posts as this post will be skipping the actual client generation process.

Using NSwag to Generate C# Client Classes for ASP.NET Core 3
Use HTTP Client Factory with NSwag Generated Classes in ASP.NET Core 3

With the client-generated and in our local Apis directory in the Razor Pages project we can now work on getting it configured and registered for use in our new project. First, open the apppsetting.json file and add a setting for the URL of our API, which is the ContactsApi value in the following sample.

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*",
  "ContactsApi": "https://localhost:5001"
}

Next, in the ConfigureServices function of the Startup class we need to register a HTTP Client for our API.

public void ConfigureServices(IServiceCollection services)
{
    services.AddRazorPages()
            .AddNewtonsoftJson();

    services.AddHttpClient<IContactsClient, 
                           ContactsClient>(client => 
             client.BaseAddress = new Uri(Configuration.GetSection("ContactsApi").Value));
}

Add Pages

Now that our API access is set up we need to create pages that will allow users to interact with the API. To start add a Contacts directory to the existing Pages directory so all of the pages that deal with interacting with the Contacts API will be together.

CAUTION the next bit may or may not be helpful. I wanted to generate the UI for the Contact pages instead of having to manually create them using the scaffolding, but it needs Entity Framework to work and this new project doesn’t use Entity Framework. This section is going to walk through adding a temporary reference to the API project, since it does use Entity Framework, in order to generate the related UI. Feel free to skip this part if you want to manually create your associated UI.

In the API project add the following temparary changes to the ContactsDbContext class.

public ContactsDbContext() {}

protected override void OnConfiguring(DbContextOptionsBuilder options) => 
          options.UseSqlite("Data Source=app.db");

Now we need to add a temporary reference to the API project from the Razor Pages project. To do this right-click on the Dependencies node in Razor Pages project and select Add Reference.

In the Projects section check the box for the API project and click OK.

Now with the above in place, we can scaffold our UI. Right-click on the folder where you want the resulting UI to live, the Pages/Contacts directory in our case. From the menu select Add > New Scaffolded Item.

On the dialog that shows we want to select Razor Pages using Entity Framework (CRUD) and then click Add.

On the next screen we will be selecting the Model class and Data context class from the API project for the entity we are generating the UI for and then clicking Add.

After a few seconds, all the pages we need to view, create, edit, and delete contacts will exist. Now that we have our pages generated we need to remove the reference to the API project. To do this expand the Dependencies > Projects node and right-click on the API project and select Remove.

Also, revert the changes we made to the DbContext above.

Now that the reference to the API project is gone the Razor Pages application won’t build. This is expected as it was using some classes from the API project. We are going to walk through the edits needed to fix the issues in the Index page in the Contacts directory, but the same type of changes will be needed in all the generated classes.

First, we need to change some usings. Remove any Entity Framework related usings. Then change any related to the Contacts API to instead reference the API client local to the project.

Before:
using Microsoft.EntityFrameworkCore;
using ContactsApi.Data;
using ContactsApi.Models; 

After:
using Apis;

The other big item is to replace the injection of the Entity Framework DB Context with the API Client and update the related calls with calls to the API. The following is the IndexModel with the Entity Framework bits present.

public class IndexModel : PageModel
{
    private readonly ContactsApi.Data.ContactsDbContext _context;

    public IndexModel(ContactsApi.Data.ContactsDbContext context)
    {
        _context = context;
    }

    public IList<Contact> Contact { get;set; }

    public async Task OnGetAsync()
    {
        Contact = await _context.Contacts.ToListAsync();
    }
}

And here is the end result using the API Client.

public class IndexModel : PageModel
{
    private readonly IContactsClient _client;

    public IndexModel(IContactsClient client)
    {
        _client = client;
    }

    public IList<Contact> Contact { get;set; }

    public async Task OnGetAsync()
    {
        Contact = (await _client.GetContactsAsync()).ToList();
    }
}

And as stated above this kind of thing would need to be repeated for the other generated pages.

END CAUTION

Add to Navigation Bar

Now that we have our pages created we need to add a way for the user to get to them. To do this we are going to add a Contacts option to the navigation bar. Open the Pages/Shared/_Layout.cshtml file. The easiest way to locate where the change needs to go is to search for the text of one of the existing navigation links. The following is the links section with the new items added.

<ul class="navbar-nav flex-grow-1">
    <li class="nav-item">
        <a class="nav-link text-dark" asp-area="" asp-page="/Index">Home</a>
    </li>
    <li class="nav-item">
        <a class="nav-link text-dark" asp-area="" asp-page="Contacts/Index">Contacts</a>
    </li>
    <li class="nav-item">
        <a class="nav-link text-dark" asp-area="" asp-page="/Privacy">Privacy</a>
    </li>
</ul>

Wrapping Up

Using Nswag’s generated client makes it super simple to connect an application to an API, not that doing it manually is hard per se. Most of this post ended up being about my detour to generate the UI in the client application. Was it worth it? I’m not sure. I guess either way it is nice to know it is an option when you have the Entity Framework data available.

Here is the code in the final state from this post.

Use HTTP Client Factory with NSwag Generated Classes in ASP.NET Core 3

In last week’s post, Using NSwag to Generate C# Client Classes for ASP.NET Core 3, we left off with a usable client, but we were missing out on using some of the features provided by ASP.NET Core such as the HTTP Client Factory and utilizing dependency injection.

Changes to NSwag Client Generation

This post is only going to point out the difference needed to help enable utilization of the ASP.NET Core features mentioned above and won’t be a full walkthrough of using NSwag. If you need a reference for what this post is covering make sure and read last week’s post.

The one change needed from last week’s post is to check Generate interfaces for Client classes.

With the above checked the client class can be regenerated and the files in the consuming application updated.

Using HTTP Client Factory and Dependency Injection

In the consuming application, we need to add the following to line in the ConfigureServices function of the Startup class to add an HTTP Client specifically for our Contacts API and make it available via the dependency injection system.

services.AddHttpClient<IContactsClient, ContactsClient>(client => 
           client.BaseAddress = new Uri("https://localhost:5001"));

For a production application, I would recommend using the configuration system to store the URL for the API instead of hardcoded like it is above.

For example usage, I’m using the IndexModel. First,  add a class-level field to hold our API client and inject the client via the constructor.

private readonly IContactsClient _contactsClient;

public IndexModel(ILogger<IndexModel> logger, IContactsClient contactsClient)
{
    _logger = logger;
    _contactsClient = contactsClient;
}

Now that we have a contacts client at the class-level we can use it get data from our API. The following example uses the client to get all the contacts from the API and stores them in a variable.

public async Task OnGet()
{
    var contacts = await _contactsClient.GetContactsAsync();
}

Wrapping Up

I highly recommend using this style of client vs. using HTTP client directly. If you do some searching you will find that managing the lifetime of HTTP client in .NET before the HTTP client factory was something that is easy to screw up.

The following posted were used as references:

Generating a Typed Client for use with HttpClientFactory using NSwag
How to add generated HttpClient to ASP.NET Core dependency injection

Using NSwag to Generate C# Client Classes for ASP.NET Core 3

This post is going to use one of the tools provided by NSwag to generate C# client classes to provide access to an API. While the NSwag tooling provides multiple ways to discover the definition of an API we will be using the tooling to generate C# classes from an OpenAPI/Swagger specification.

For details on how to use NSwag to provide OpenAPI/Swagger for your APIs check out my Swagger/OpenAPI with NSwag and ASP.NET Core 3 post. You can grab the API I’m using in the post from this GitHub repo if you need an API to play around with. If you do grab the sample API from GitHub not that it does use Entity Framework Core and SQLite which means you will need to create the associated database. Details of how to do that can be found in the Create and Apply Initial Migration section of my ASP.NET Core 3: Add Entity Framework Core to Existing Project post.

Sample Client Application

For this example, we will spin up a Razor Pages application using the .NET CLI with the following command from your favorite terminal application in the directory you want the application created.

dotnet new webapp

NSwag Client Generation

NSwag provides multiple options for client generation including a CLI option, code, and a Windows application. This post is going to use the Windows application which is called NSwagStudio. Download and install NSwagStudio from here.

Next, make sure your API is running and get the URL of its OpenAPI/Swagger specification URL. For example, I am using a local instance of my API and the URL I need is https://localhost:5001/swagger/v1/swagger.json. If you are using the Swagger UI you can find a link to your swagger.json under the API title.

Now that we have the OpenAPI/Swager specification URL for the API we are dealing with open NSwagStudio. The application will open with a new document ready to go. There are a few options we will need to set. First, we want to use the NetCore30 Runtime. Next, select the OpenAPI/Swagger Specification tab and enter your API’s specification URL in the Specification URL box.

In the Outputs section check the CSharp Client checkbox and then select the CSharp Client tab. As you can see from the screenshot below there are a ton of options to tweak. For this example, we are taking the defaults for all of them except for Namespace, which I set to ContactsApi, and Output file path, which is only needed if you use the Generate Files option. Click the Generate Files button and NSwagStudio will create a file that contains all the code needed to access the API described in the OpenAPI/Swager specification selected in the Input section.

Note, the Generate Outputs button can be used if you want to see what the generated code will look in the Output tab on the same level as Settings.

Use Generated Client from the Sample Project

In the sample project, I created an APIs directory and dropped the ContactsApi.cs created with NSwagStudio there. The files generated with NSwagStudio are expecting JSON.NET to be present so the sample project will need a reference to the Microsoft.AspNetCore.Mvc.NewtonsoftJson NuGet package.

Now that the project has a reference to JSON.NET in the ConfigureServices function of the Startup class we need to tell the app to make JSON.NET available via dependency injection with the following change.

services.AddRazorPages()
        .AddNewtonsoftJson();

Now to test out the client I used the following OnGet function in the Index.cshtml.cs file.

public async Task OnGet()
{
    using (var httpClient = new HttpClient())
    {
        var contactsClient = new ContactsClient(httpClient);
        var contacts = await contactsClient.GetContactsAsync();
    }
}

Note the above is only meant to show that the generated client work and isn’t meant to be a production-grade example. For more production-grade scenarios make sure and following Microsoft’s guidance on HTTP client usage.

Wrapping Up

NSwag’s client generation seems to be an easy way to get started consuming API’s. I’m not sure if the CLI would provide more options for how the client code is generated or not with support of HTTPClientFactory and strongly typed HTTP Clients. This will be something I may explorer more in a future post.

Entity Framework Core: No database provider has been configured for this DbContext

When writing ASP.NET Core 3: Add Entity Framework Core to Existing Project I got to the point where I was going to add my initial Entity Framework Core migration when I got a huge error message with the last bit being the following in red.

No database provider has been configured for this DbContext. A provider can be configured by overriding the DbContext.OnConfiguring method or by using AddDbContext on the application service provider. If AddDbContext is used, then also ensure that your DbContext type accepts a DbContextOptions<TContext> object in its constructor and passes it to the base constructor for DbContext.

State of the Project

The project I was working on was an API that had a single model defined as the following.

public class Contact
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Address { get; set; }
    public string City { get; set; }
    public string State { get; set; }
    public string PostalCode { get; set; }
    public string Phone { get; set; }
    public string Email { get; set; }
}

And the DbContext looked like this.

public class ContactsDbContext : DbContext
{
    public DbSet<Contact> Contacts { get; set; }
}

Finally the ConfigureServices function of Startup.

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<ContactsDbContext>(options =>
        options.UseSqlite(Configuration.GetConnectionString("DefaultConnection")));
    services.AddControllers();
}

The Error

At this point, I ran the following command from the command prompt to add a migration.

dotnet ef migrations add Initial

Which results in the following error.

Stay Calm, Read, and Fix

Don’t make the same mistake I did and runoff and double-check everything in your application. The yellow and red sections of the exception message tell you what the fix should be.

In the case of the application in question, I wanted to use the connection string setup in Startup.ConfigureServices. To do that, as the error states if you bother to read it, the DbContext needs a constructor added that takes a DbContextOptions and passes that value to the base class’ constructor like the following.

public ContactsDbContext(DbContextOptions<ContactsDbContext> options) : base(options)
{ }

Alternatively, if you aren’t to the point in your application that you want to get your database information from configuration you can override OnConfiguring in your DbContext and set your connection string there like the following.

protected override void OnConfiguring(DbContextOptionsBuilder options)
    => options.UseSqlite("DataSource=app.db");

I don’t recommend the second option, but since it is valid I feel like it needs to be included.

Wrapping Up

For me, this served as a good reminder to slow down and actually read errors even if they are a wall of text. Hopefully making myself write this post will help this lesson stick.