Entity Framework Code first making a column non-nullable

问题

I am using EF code first for my project. I have following code in my DataModel

[HiddenInput(DisplayValue = false)]        
public DateTime? PasswordDate { get; set; }

To make this non-nullable I removed '?' and ran Add-Migration command from Package manager console. following migration file was generated.

  public partial class PasswordDate : DbMigration
{
    public override void Up()
    {
        AlterColumn("dbo.CertificateInfoes", "PasswordDate", c => c.DateTime(nullable: false));
    }

    public override void Down()
    {
        AlterColumn("dbo.CertificateInfoes", "PasswordDate", c => c.DateTime());
    }
}

But when I run Update-Database command:

Update-Database -SourceMigration 201309020721215_PasswordDate

I get following error: Cannot insert the value NULL into column 'PasswordDate', table ''; column does not allow nulls. UPDATE fails. The statement has been terminated.

Kindly suggest the solutions.

回答1:

That's because you allowed NULL values in that column, then tried to make it non-nullable. It will subsequently try to migrate your existing data into that newly non-nullable column, which will break because you already have NULL values in there.

Two solutions:

1) Change it back to nullable
2) Give it a default value for items that don't have a value.

回答2:

It's not possible to directly add a non-nullable column to a table that has historical data in the table if no default value is provided for that column.

What I do is

add the column as nullable.
provide an sql script to populate this newly added column.
alter the column to make is as non-nullable.

Code example(with postgres database):

 public override void Up()
    {            
        AddColumn("public.YourTableName", "YourColumnName", c => c.Int(nullable: true));
        Sql(@"UPDATE ""public"".""YourTableName""
              SET ""YourColumnName"" = Value you want to set
            ");

        AlterColumn("public.YourTableName", "YourColumnName", c => c.Int(nullable: false));
    }

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

标签

sql

entity-framework