EF 中的 GUID COMB 策略 [英] GUID COMB strategy in EF

问题描述

在新的 Entity Framework 4.1 中，有没有办法使用 CodeFirst 设计为对象实现 Guid COMB 标识策略?我认为设置 StoreGeneratedPattern 会起作用，但它仍然给我正常的 GUID.

Is there any way to implement the Guid COMB identity strategy for objects in the new Entity Framework 4.1 using the CodeFirst design? I thought setting the StoreGeneratedPattern would work, but it still gives me normal GUIDs.

推荐答案

我猜你正在使用 SQL 服务器作为你的数据库.这是不同 MS 工具之间不一致的一个很好的例子.SQL Server 团队不建议使用 newid() 作为 UNIQUEIDENTIFIER 列的默认值，如果您指定 Guid 属性，ADO.NET 团队会使用它在数据库中自动生成.他们应该使用 newsequentialid() 代替！

I guess you are using SQL server as your database. This is nice example of inconsistency among different MS tools. SQL server team doesn't recommend using newid() as default value for UNIQUEIDENTIFIER columns and ADO.NET team use it if you specify Guid property as autogenerated in the database. They should use newsequentialid() instead!

如果你想要由数据库生成的顺序 Guid，你必须修改生成的表，它真的很复杂，因为你必须找到自动生成的默认约束，删除它并创建新的约束.这一切都可以在自定义数据库初始化程序中完成.这是我的示例代码:

If you want sequential Guids generated by database you must modify generated table and it is really complex because you must find autogenerated default constraint, drop it and create new constraint. This all can be done in custom database initializer. Here you have my sample code:

class Program
{

    static void Main(string[] args)
    {
        Database.SetInitializer(new CustomInitializer());
        using (var context = new Context())
        {
            context.TestEntities.Add(new TestEntity() { Name = "A" });
            context.TestEntities.Add(new TestEntity() { Name = "B" });
            context.SaveChanges();
        }
    }
}

public class CustomInitializer : DropCreateDatabaseAlways<Context>
{
    protected override void Seed(Context context)
    {
        base.Seed(context);

        context.Database.ExecuteSqlCommand(@"
            DECLARE @Name VARCHAR(100)

            SELECT @Name = O.Name FROM sys.objects AS O
            INNER JOIN sys.tables AS T ON O.parent_object_id = T.object_id
            WHERE O.type_desc LIKE 'DEFAULT_CONSTRAINT' 
              AND O.Name LIKE 'DF__TestEntities__Id__%'
              AND T.Name = 'TestEntities'

            DECLARE @Sql NVARCHAR(2000) = 'ALTER TABLE TestEntities DROP Constraint ' + @Name

            EXEC sp_executesql @Sql

            ALTER TABLE TestEntities
            ADD CONSTRAINT IdDef DEFAULT NEWSEQUENTIALID() FOR Id");
    }
}

public class TestEntity
{
    public Guid Id { get; set; }
    public string Name { get; set; }
}

public class Context : DbContext
{
    public DbSet<TestEntity> TestEntities { get; set; }

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

        modelBuilder.Entity<TestEntity>()
            .Property(e => e.Id)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
    }
}

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