具有链接表的实体框架代码优先迁移问题

Question

I'm using EF 5.0 code first, using automatic migrations via the PM console.

I'm attempting to apply a 4th migration to a project and the convention based naming of my linking tables is causing them to be dropped and recreated with a different name. This has not occurred during any of the previous migrations.

Example :

I have 2 classes User and Site.

InitialCreate Migration

This created a link table called "UserSites" by convention.

CreateTable(
           "dbo.UserSites",
            c => new
                {
                    User_Id = c.Guid(nullable: false),
                    Site_Id = c.Guid(nullable: false),
                })
            .PrimaryKey(t => new { t.User_Id, t.Site_Id })
            .ForeignKey("dbo.Users", t => t.User_Id, cascadeDelete: true)
            .ForeignKey("dbo.Sites", t => t.Site_Id, cascadeDelete: true)
            .Index(t => t.User_Id)
            .Index(t => t.Site_Id);

Everything works well.

Skip to today :

4th Migration

This drops the UserSites link table and creates a SiteUsers link table.

Obviously not ideal!

public override void Up()
    {
        DropForeignKey("dbo.UserSites", "User_Id", "dbo.Users");
        DropForeignKey("dbo.UserSites", "Site_Id", "dbo.Sites");
        DropIndex("dbo.UserSites", new[] { "User_Id" });
        DropIndex("dbo.UserSites", new[] { "Site_Id" });


        CreateTable(
            "dbo.SiteUsers",
            c => new
                {
                    Site_Id = c.Guid(nullable: false),
                    User_Id = c.Guid(nullable: false),
                })
            .PrimaryKey(t => new { t.Site_Id, t.User_Id })
            .ForeignKey("dbo.Sites", t => t.Site_Id, cascadeDelete: true)
            .ForeignKey("dbo.Users", t => t.User_Id, cascadeDelete: true)
            .Index(t => t.Site_Id)
            .Index(t => t.User_Id);

        DropTable("dbo.UserSites");

I'm at a loss to explain this.

Neither class has changed since the first implementation... and I presume if I apply this I will suffer data loss.

So to the question(s) :

1. Can I just remove this code from the migration script and continue using my existing structure?

2. Is there a gotcha that I don't know about that might have caused this?

Any/all assistance much appreciated!

Edit:

I have simply defined the classes as below and allowed the model to be built by convention. I have changed the namespace of the dbcontext, but that is all! Colour me bewildered.

public class User
{
   public virtual ICollection<Site> Sites { get; set; }
}

public class Site
{
    public virtual ICollection<User> Users { get; set; }
}

Answer 1

It's a strange situation. Did you change anything in your DbContext ? How you declare Sites and Users properties in your classes?

I think you should explicit add many-to-many relationship to your db context, like this:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);

    modelBuilder.Entity<User>()
                .HasMany<Sites>(u => u.Sites)
                .WithMany(e => e.Users)
                .Map(
                    m =>
                        {
                            m.MapLeftKey("User_Id");
                            m.MapRightKey("Site_Id");
                            m.ToTable("UserSites");
                        });

    //for prevent error 'The referential relationship will result in a cyclical reference that is not allowed'
    modelBuilder.Entity<Sites>()
                .HasRequired(s => s.User)
                .WithMany()
                .WillCascadeOnDelete(false);
}

Then remove your 4th migration and try to add it again

If you remove your migration code, you'll catch navigation errors like foreign keys problem, incorrect table name, etc.