如何在实体框架4代码中首先映射复合主键?

I'm getting to grips with EF4 code first, and liking it so far. But I'm having trouble mapping an entity to a table with a composite primary key.

我首先接触到EF4代码，到目前为止我很喜欢它。但是我在用复合主键将实体映射到表时遇到了麻烦。

The configuration I've tried looks like this:

我试过的配置是这样的:

public SubscriptionUserConfiguration()

    {
                Property(u => u.SubscriptionID).IsIdentity();
                Property(u => u.UserName).IsIdentity();
    }

Which throws this exception: Unable to infer a key for entity type 'SubscriptionUser'.

这将引发此异常:无法推断实体类型“SubscriptionUser”的键。

What am I missing?

我缺少什么?

4 个解决方案

#1

You could also use

您还可以使用

HasKey(u => new { u.SubscriptionID, u.UserName });

Edit:

编辑:

One limitation I have found is that the following do not work:

我发现的一个局限性是，以下方法不起作用:

public ProjectAssignmentConfiguration()
{
    HasKey(u => u.Employee.EmployeeId);
    HasKey(u => u.Project.ProjectId);
}

或

public ProjectAssignmentConfiguration()
{
    HasKey(u => new { u.Employee.EmployeeId, u.Project.ProjectId });
}

So how do you set up an entity where the join table has a primary key that is composed of foreign keys?

那么如何设置一个实体，使联接表具有由外键组成的主键?

#2

I will try to explain it step by step, using the following Entity

我将尝试使用以下实体一步一步地解释它

public class Account
{
    public int AccountId1 { get; set; }
    public int AccountId2 { get; set; }
    public string Description { get; set; }
}

Create a class derived from the EntityTypeConfiguaration<TEntity> Object to override the conventions

创建一个派生自EntityTypeConfiguaration 对象的类，以覆盖这些约定

class AccountEntityTypeConfiguration : EntityTypeConfiguration<Account>
{

    public AccountEntityTypeConfiguration()
    {
      // The Key
      // The description of the HasKey Method says
      // A lambda expression representing the property to be used as the primary key.
      // If the primary key is made up of multiple properties then specify an anonymous type including the properties.
      // Example C#: k => new { k.Id1, k.Id2 }
      // Example VB: Function(k) New From { k.Id1, k.Id2 }
      this.HasKey(k => new { k.AccountId1, k.AccountId2 } );  // The Key

      // Maybe the key properties are not sequenced and you want to override the conventions
      this.Property(p => p.AccountId1).HasDatabaseGeneratedOption(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.None);
      this.Property(p => p.AccountId2).HasDatabaseGeneratedOption(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.None);

      this.Property(p => p.Description).IsRequired();  // This property will be required
      this.ToTable("Account");  // Map the entity to the table Account on the database
    }
}

When create the class derived from the DbContext Object, override OnModelCreating Method and add a new AccountEntityTypeConfiguration object to the Configurations of the model Builder.

当创建从DbContext对象派生的类时，重写onmodelcreation方法，并向模型构建器的配置添加一个新的AccountEntityTypeConfiguration对象。

public class MyModelAccount : DbContext
{
    public DbSet<Account> Accounts { get; set;}

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        // Add a new AccountEntityTypeConfiguration object to the configuration of the model, that will be applied once the model is created. 
        modelBuilder.Configurations.Add(new AccountEntityTypeConfiguration());
    }

}

Hope it helps you!

希望它能帮助你!

#3

You can also use the Column attribute

您还可以使用Column属性

public class UserProfileRole
{
    [Key, Column(Order = 0)]
    public int UserId { get; set; }

    [Key, Column(Order = 1)]
    public int RoleId { get; set; }
}

#4

Solved it: I should be using HasKey, not Identity. This works:

解决它:我应该使用HasKey，而不是Identity。如此:

public SubscriptionUserConfiguration()
{
     HasKey(u => u.SubscriptionID);
     HasKey(u => u.UserName);
}

#1