Entity Framework Core with SQLite Migration Limitations
This is part of what has turned into a series on Entity Framework Core with SQLite. The other parts can be found below.
Entity Framework Core with SQLite
Entity Framework Core Errors Using Add-Migration
Entity Framework Core with SQLite Scaffolding
The starting point of the code for this post can be found here.
Migration Limitations when using SQLite
SQLite’s ALTER TABLE is limited which in turn limits what Entity Framework Core can do via a migration. The official docs on the subject can be found here. These limitations are on the Entity Framework Team’s list of issues as an open enhancement and can be tracked here.
As long as you are just adding new tables or columns you would never notice the limitation, but if you have spelling problems like I do then the need to rename a column can be important. Thankfully things like ReSpeller (link is to the pro page, but a free version is available in ReSharpers extension manager) help with my spelling issues.
Unsupported example with a column rename
As an example of how to handle a migration that isn’t supported, we are going to rename the State property of the Contact class to Subregion.
Rename property on the model
Open the Contact class which can be found in the Models directory and make the following change.
Before:
public string State { get; set; }
After:
public string Subregion { get; set; }
Add a migration
With the property name change using the following command in the Package Manager Console to create a new migration.
Add-Migration RenameContactStateToSubregion -c ContactsDbContext
Which produces the following migration class.
public partial class RenameContactStateToSubregion : Migration
{
protected override void Up(MigrationBuilder migrationBuilder)
{
migrationBuilder.RenameColumn(
name: "State",
table: "Contacts",
newName: "Subregion");
}
protected override void Down(MigrationBuilder migrationBuilder)
{
migrationBuilder.RenameColumn(
name: "Subregion",
table: "Contacts",
newName: "State");
}
}
Error trying to apply the migration
As expected when an attempt to apply the above migration results in the following exception.
System.NotSupportedException: SQLite does not support this migration operation (‘RenameColumnOperation’). For more information, see http://go.microsoft.com/fwlink/?LinkId=723262.
Modify migration to manually rename the column
Searching for how to rename a column in SQLite will turn up a lot of results including this from the official docs and answers like this on StackOverflow. The gist of the how to do a rename is to create a new table with the desired schema, copy the data from the original table, drop the old table, and finally rename the new table to match the original name.
Now knowing the process the migration above can be modified to apply SQL directly instead of using Entity Framework Core to generate the SQL. This can be done by using the Sql function of the MigrationBuilder class. The following is the resulting migration.
public partial class RenameContactStateToSubregion : Migration
{
protected override void Up(MigrationBuilder migrationBuilder)
{
migrationBuilder.Sql(
@"PRAGMA foreign_keys = 0;
CREATE TABLE Contacts_temp AS SELECT *
FROM Contacts;
DROP TABLE Contacts;
CREATE TABLE Contacts (
Id INTEGER NOT NULL
CONSTRAINT PK_Contacts PRIMARY KEY AUTOINCREMENT,
Address TEXT,
City TEXT,
Email TEXT,
Name TEXT,
Phone TEXT,
PostalCode TEXT,
Subregion TEXT
);
INSERT INTO Contacts
(
Id,
Address,
City,
Email,
Name,
Phone,
PostalCode,
Subregion
)
SELECT Id,
Address,
City,
Email,
Name,
Phone,
PostalCode,
State
FROM Contacts_temp;
DROP TABLE Contacts_temp;
PRAGMA foreign_keys = 1;");
}
protected override void Down(MigrationBuilder migrationBuilder)
{
}
}
You will notice that I didn’t bother doing the Down function, but the same idea would apply when trying to undo a migration. SQLiteStudio or similar tools can be used to generate the SQL above if SQL isn’t something you want to deal with.
Fix other references to the renamed field
This isn’t really the topic of this post, but I wanted to throw in a reminder that after a rename like this there are places that will need to be updated that the tooling may not have picked up. For example, make sure all your views are using the new column as well as any bind statements in your controllers.
Wrapping up
The first time I hit the need to rename a column and it resulted in an exception it was extremely frustrating. Over time as I learned what the tooling around SQLite provides it has become less of an issue. I look forward to seeing what the Entity Framework team does in the future around this issue. The finished code can be found here.
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