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

问题描述

有什么办法来实现使用codeFirst设计在新的实体框架4.1对象的GUID COMB身份策略？我以为设置 StoreGeneratedPattern 会的工作，但它仍然给了我正常的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

我猜你使用SQL服务器作为数据库。这是不同的MS工具之间的不一致很好的例子。 SQL Server团队不推荐使用 NEWID（）为 UNIQUEIDENTIFIER默认值列和ADO.NET团队使用它如果指定的Guid 属性作为自动生成在数据库中。他们应该用 NEWSEQUENTIALID（），而不是！

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!

如果您想通过数据库生成连续的GUID您必须修改生成的表，这是非常复杂的，因为你必须找到自动生成的默认约束，放弃它，创造新的约束。这一切都可以自定义数据库初始化完成。在这里，你有我的样本code：

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);
    }
}

这篇关于在EF GUID COMB策略的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！