EF 4.3.1 Migration Exception - AlterColumn defaultValueSql creates same default constraint name for different tables

Question

I have a DB that I created using the OOB database initializer, and I am using Code First with EF 4.3.1.

I wanted to take advantage of the new \"IgnoreChanges\" flag

Answer 1

It seems it's a known bug: msdn forums

Andrew J Peters Microsoft (MSFT) replied:

Thanks for reporting this. The issue will be fixed for RTM.

A possible workaround is to initially make the column nullable, which will prevent Migrations from generating the extra DEFAULT constraint. Once the column is created, then it can be altered back to non-nullable.

But it's definitelly not fixed in EF 4.3.1. Here is relevant part of the source:

// Type: System.Data.Entity.Migrations.Sql.SqlServerMigrationSqlGenerator
// Assembly: EntityFramework, Version=4.3.1.0, 
// Culture=neutral, PublicKeyToken=b77a5c561934e089
namespace System.Data.Entity.Migrations.Sql
{
  public class SqlServerMigrationSqlGenerator : MigrationSqlGenerator
  {
     protected virtual void Generate(AlterColumnOperation alterColumnOperation)
     {
      //...
      writer.Write("ALTER TABLE ");
      writer.Write(this.Name(alterColumnOperation.Table));
      writer.Write(" ADD CONSTRAINT DF_");
      writer.Write(column.Name);
      writer.Write(" DEFAULT ");
      //...

So EF doesn't try to make the constraint name unique.

You should try the workaround and report it as a bug.

EDIT: I've just realized that above mentioned Generate method is virtual so in the worst case you can inherit from SqlServerMigrationSqlGenerator and fix the SQL generation and set it as the sql generator in Configuration.cs:

public Configuration()
{
    AutomaticMigrationsEnabled = true;
    SetSqlGenerator("System.Data.SqlClient", 
        new MyFixedSqlServerMigrationSqlGenerator());
}

EDIT 2:

I think the best thing to do until it fixed to fall back to raw SQL:

public override void Up()
{
    Sql(@"ALTER TABLE [CustomerLocations] ADD CONSTRAINT 
        DF_CustomerLocations_DateLastUpdated 
        DEFAULT GETDATE() FOR [DateLastUpdated]");
    Sql(@"ALTER TABLE [CustomerLocations] ALTER COLUMN 
        [DateLastUpdated] [datetime]");
    //...
}