EF5 Code First – Changing A Column Type With Migrations

The smartest way is probably to not alter types. If you need to do this, I’d suggest you to do the following steps:

1. Add a new column with your new type
2. Use Sql() to take over the data from the original column using an update statement
3. Remove the old column
4. Rename the new column

This can all be done in the same migration, the correct SQL script will be created. You can skip step 2 if you want your data to be discarded. If you want to take it over, add the appropriate statement (can also contain a switch statement).

Unfortunately Code First Migrations do not provide easier ways to accomplish this.

Here is the example code:

AddColumn("dbo.People", "LocationTmp", c => c.Int(nullable: false));
Sql(@"
    UPDATE dbp.People
    SET LocationTmp =
        CASE Location
            WHEN 'London' THEN 1
            WHEN 'Edinburgh' THEN 2
            WHEN 'Cardiff' THEN 3
            ELSE 0
        END
    ");
DropColumn("dbo.People", "Location");
RenameColumn("dbo.People", "LocationTmp", "Location");