Entity Framework Code First: Make column nullable in ASP.Net Core

Hi lingers,

You need to override the Up and Down method.

First add the column with a default value, then drop the default value.

protected override void Up(MigrationBuilder migrationBuilder)
{
    // Add the column with a default value, then drop the default value.
    // This creates a non-nullable column without the migration failing because of existing data.
    migrationBuilder.AddColumn<int>(
            name: "ColumnName",
            table: "TableName",
            type: "int",
            nullable: false,
            defaultValue: 1); // Default value

    migrationBuilder.AlterColumn<int>(
            name: "ColumnName", 
            table: "TableName",
            oldDefaultValue: 1,
            defaultValue: null);
}

protected override void Down(MigrationBuilder migrationBuilder)
{
    migrationBuilder.DropColumn(
        name: "ColumnName",
        table: "TableName");
}

Reference:

https://stackoverflow.com/questions/18569003/entity-framework-code-first-making-a-column-non-nullable