多对多、poco、ef4

Question

我有 3 个实体：

Goods [GID(PK), GoodName]
Persons [PID(PK), PersonName]
Roles [RID(PK), RoleName]

但现在我需要将这些对象相互关联。 换句话说，每个商品可以有许多人担任许多角色。 我在数据库中有一个包含 3 个字段（GID、PID、RID）的表，

例如：

Book (GID#1), can have 3 associated persons:

1. Jack (PID#1) in role Author (RID#1)
2. Jack (PID#1) in role Editor (RID#2)
3. Bill (PID#2) in role Painter (RID#3)

如何在实体框架 4 中以 POCO 格式映射它？

Answer 1

我相信您必须创建另一个 PersonRoles 标头，在其中存储 Person-Role 关系，然后通过以下标头访问 person+role：

PersonRoles [PRID(PK), PersonName, RoleName] （注意：您也可以使用实体键（仅关系）来执行此操作，EF 将消除该实体并提供直接的 Person.Roles 实体，您可以通过 Book.Persons.Select((p) p.Roles) 访问它代码>）。

PersonRole#1: Jack#1/Author#1
PersonRole#2: Jack#1/Editor#2
PersonRole#3: Bill#2/Painter#3

Book.PersonRole = context.PersonRoles.
  SingleOrDefault((pr) => pr.Person.PersonId == 1 && pr.RoleId == 1);

注意：我的主要语言是 VB.NET，所以我对上面的伪代码表示歉意，但我希望你能明白。

更新

它应该是这样的：（

<DataContract(IsReference:=True)>
<KnownType(GetType(Good))>
<KnownType(GetType(Person))>
<KnownType(GetType(Role))>
Partial Public Class GoodPersonRole
    Implements IObjectWithChangeTracker
    Implements INotifyPropertyChanged

<DataMember()>
Public Property GoodId() As Integer
    Get
        Return _goodId
    End Get
    Set(ByVal value As Integer)
        If Not Equals(_goodId, value) Then
            If ChangeTracker.ChangeTrackingEnabled AndAlso ChangeTracker.State <> ObjectState.Added Then
                Throw New InvalidOperationException("The property 'GoodId' is part of the object's key and cannot be changed. Changes to key properties can only be made when the object is not being tracked or is in the Added state.")
            End If
            If Not IsDeserializing Then
                If Good IsNot Nothing AndAlso Not Equals(Good.GoodId, value) Then
                    Good = Nothing
                End If
            End If
            _goodId = value
            OnPropertyChanged("GoodId")
        End If
    End Set
End Property

Private _goodId As Integer


<DataMember()>
Public Property Good() As Good
    Get
        Return _good
    End Get
    Set(ByVal value As Good)
        If _good IsNot value Then
            If ChangeTracker.ChangeTrackingEnabled AndAlso ChangeTracker.State <> ObjectState.Added AndAlso value IsNot Nothing Then
                ' This the dependent end of an identifying relationship, so the principal end cannot be changed if it is already set,
                ' otherwise it can only be set to an entity with a primary key that is the same value as the dependent's foreign key.
                If Not Equals(GoodId, value.GoodId) Then
                    Throw New InvalidOperationException("The principal end of an identifying relationship can only be changed when the dependent end is in the Added state.")
                End If
            End If
            Dim previousValue As Good = _good
            _good = value
            FixupGood(previousValue)
            OnNavigationPropertyChanged("Good")
        End If
    End Set
End Property
Private _good As Good
End Class

来自 ADO.NET VB POCO 实体生成器）

我刚刚复制了“良好”ID 和导航。财产不过应该是他们三个人的。