EF Core migrationBuilder.AlterColumn change existing values

Question

One of my developers has created several new columns on the database as a string. These contain "Yes"/"No" values.

It would be better to convert the columns to a bool.

The Up method on the migrations gives this code

     migrationBuilder.AlterColumn<bool>(
            name: "IsContractor",
            table: "Employee",
            type: "boolean",
            nullable: false,
            oldClrType: typeof(string),
            oldType: "text");

Is there a way when updating the column I can migrate the value i.e.

IsContractor == "Yes"; // will set it to true / false

Answer 1

I would suggest to first add a new column "IsContractorBool" for the boolean value, retaining the old one.

Then execute something like

migrationBuilder.Sql(
    @"Update Employee 
      SET IsContractorBool = CASE
          WHEN IsContractor LIKE 'Yes' then true
          ELSE false
      END"
);

to migrate the data.

After that you can delete the old text based column and optionally rename column "IsContractorBool" .