關聯性 (中繼資料)

實體資料模型 (EDM) 中的關聯性 (Relationship) 會定義兩個實體 (Entity) 彼此相關的方式。 Entity Data Model 關聯性主題會提供 EDM 中關聯性的相關詳細資訊。

ADO.NET 中繼資料 (Metadata) 會提供 AssociationType 來代表 EntityType 之間的關聯性。AssociationType 衍生自 RelationshipType 而且代表 EDM 關聯。 同樣地，AssociationSet 會描述參與特定 EDM 關聯的 EntitySet。 如需實體集和關聯集的詳細資訊，請參閱實體集 (EDM) 和關聯集 (EDM)。

下列程式碼範例會示範如何從連接中取得中繼資料工作空間，然後使用該中繼資料工作空間來擷取指定之模型內有關關聯性的資訊。 請注意，中繼資料工作空間是一個執行階段服務元件，它會提供用來擷取中繼資料的支援。

此程式碼範例會使用 CSpace 來指定此模型。 CSpace 代表概念模型的預設名稱。

此程式碼範例包括三個方法：GetAssociations、GetAssociationSets 和 GetOneAssociationSet。

GetAssociations 方法會取得關聯的集合，然後逐一查看此集合，以便存取其關聯 End 成員。

GetAssociationSets 方法會取得實體容器的集合，然後逐一查看此集合，以便取得指定之容器內的每個關聯集。 在 EDM 中，EntityContainer 代表實體集和關聯集的邏輯群組。 如需實體容器如何在 EDM 中定義的詳細資訊，請參閱實體容器 (EDM)。

GetOneAssociationSet 方法會取得實體容器的集合，然後逐一查看此集合，以便使用指定的名稱來單獨取得一個關聯集。

下列程式碼會使用 AdventureWorks 完整模型 (EDM) 主題所提供的 Adventureworks 模型。 如需應用程式組態檔的範例，請參閱使用 AdventureWorks 物件模型 (EDM)。

using System;
using System.Data;
using System.Data.EntityClient;
using System.Data.Metadata.Edm;
using System.Collections.ObjectModel;

class GetRelationshipsExample
{
  static void Main()
  {
    try
    {
      // Establish a connection to the underlying data provider by 
      // using the connection string specified in the config file.
      using (EntityConnection connection = 
               new EntityConnection("Name=AdventureWorksEntities"))
      {
         // Open the connection.
         connection.Open();

         // Access the metadata workspace.
         MetadataWorkspace workspace = 
             connection.GetMetadataWorkspace();

         // Get associations from the conceptual model.
         GetAssociations(workspace, DataSpace.CSpace);

         // Get association sets from the conceptual model.
         GetAssociationSets(workspace, DataSpace.CSpace);

         // Get one assoiation set by using the specified 
         // relationship name from the conceptual model.
         string relationshipName = "FK_Employee_Contact_ContactID";
         GetOneAssociationSet(
           workspace, relationshipName, DataSpace.CSpace);
       }
     }
     catch (MetadataException exceptionMetadata)
     {
        Console.WriteLine("MetadataException: {0}", 
                          exceptionMetadata.Message);
     }
     catch (System.Data.MappingException exceptionMapping)
     {
        Console.WriteLine("MappingException: {0}",
                          exceptionMapping.Message);
     }
  }

  public static void GetAssociations(
   MetadataWorkspace workspace, DataSpace model)
  {
     Console.WriteLine("***Get Associations =>");
     // Get a collection of association types.
     ReadOnlyCollection<AssociationType> associationTypes = 
          workspace.GetItems<AssociationType>(model);

     // Iterate through the collection to get each association type.
     foreach (AssociationType associationType in associationTypes)
     {
        Console.WriteLine("AssociationType Name: {0}, Namespace: {1}",
                     associationType.Name,
                     associationType.NamespaceName);

        // Iterate through the collection to get 
        // each association end member.
        foreach (AssociationEndMember end in 
                        associationType.AssociationEndMembers)
        {
           Console.WriteLine(
                   "\t End Name: {0}, Type: {1}, Multiplicity: {2}",
                   end.Name,
                   end.TypeUsage.EdmType.Name,
                   end.RelationshipMultiplicity);
        }
     }
  }

  public static void GetAssociationSets(
   MetadataWorkspace workspace, DataSpace model)
  {
     Console.WriteLine("***Get Association Sets =>");
     // Get a collection of entity containers.
     ReadOnlyCollection<EntityContainer> containers = 
           workspace.GetItems<EntityContainer>(model);

     // Iterate through the collection to get each entity container.
     foreach (EntityContainer container in containers)
     {
        // Iterate through the collection to get each entity set base.
        foreach (EntitySetBase baseSet in container.BaseEntitySets)
        {
                // EntitySetBase is a super type for 
                // AssociationSet and EntitySet. 
                // Check if the current object is an instance of the 
                // AssociationSet.
                if (baseSet is AssociationSet)
                {
                    Console.WriteLine(
                     "AssociationSet Name: {0} , " +
                     "AssociationType Name: {1} ",
                     baseSet.Name, baseSet.ElementType.FullName);

                    AssociationSet associationSet = 
                                baseSet as AssociationSet;

                    // Iterate through the collection to get 
                    // each association end.
                    foreach (AssociationSetEnd end in 
                             associationSet.AssociationSetEnds)
                    {
                        Console.WriteLine(
                          "EntitySet Name: {0} , Name: {1}, " + 
                          "AssociationEndMember: {2} ",
                          end.EntitySet, 
                          end.Name, 
                          end.CorrespondingAssociationEndMember);
                    }
                }
        }
     }
  }

  public static void GetOneAssociationSet(
      MetadataWorkspace workspace, string relationshipName, 
      DataSpace model)
  {
     Console.WriteLine("***Get One AssociationSet =>");
     // Get a collection of entity containers.
     ReadOnlyCollection<EntityContainer> containers = 
            workspace.GetItems<EntityContainer>(model);

     // Iterate through the collection to get each entity container.
     foreach (EntityContainer container in containers)
     {
        RelationshipSet relationshipSet;

        // Check if the relationship with the specified name exists 
        // or not.
        if (container.TryGetRelationshipSetByName(
                      relationshipName, true, out relationshipSet))
        {
                AssociationSet associationSet = 
                                 relationshipSet as AssociationSet;
                Console.WriteLine(
                    "AssociationSet Name: {0} , " +
                    "AssociationType Name: {1} ", 
                     associationSet.Name, 
                     associationSet.ElementType.FullName);                
         }
     }
  }
}

Imports System
Imports System.Collections.ObjectModel
Imports System.Data
Imports System.Data.EntityClient
Imports System.Data.Metadata.Edm

Class GetRelationshipsExample

  Shared Sub Main()
    Try
      ' Establish a connection to the underlying data provider by 
      ' using the connection string specified in the config file.
      Using connection As EntityConnection = _
            New EntityConnection("Name=AdventureWorksEntities")
        ' Open the conection.
         connection.Open()

        ' Access the metadata workspace.
        Dim workspace As MetadataWorkspace = _
           connection.GetMetadataWorkspace

        ' Get associations from the conceptual model.
        GetAssociations(workspace, DataSpace.CSpace)

        ' Get association sets from the conceptual model.
        GetAssociationSets(workspace, DataSpace.CSpace)

        ' Get one assoiation set by using the specified 
        ' relationship name from the conceptual model.
        Dim relationshipName As String = _
          "FK_Employee_Contact_ContactID"
        GetOneAssociationSet( _
             workspace, relationshipName, DataSpace.CSpace)
      End Using
    Catch exceptionMetadata As MetadataException
       Console.WriteLine("MetadataException: {0}", _
          exceptionMetadata.Message)
    Catch exceptionMapping As MappingException
       Console.WriteLine("MappingException: {0}", _
          exceptionMapping.Message)
    End Try
  End Sub

  Public Shared Sub GetAssociations( _
    ByVal workspace As MetadataWorkspace, ByVal model As DataSpace)

    Console.WriteLine("***Get Associations =>")

    ' Get a collection of association types.
    Dim associationTypes As ReadOnlyCollection(Of AssociationType) = _
           workspace.GetItems(Of AssociationType)(model)

    ' Iterate through the collection to get each association type.
    Dim associationType As AssociationType
    For Each associationType In associationTypes
      Console.WriteLine("AssociationType Name: {0}, Namespace: {1}", _
          associationType.Name, associationType.NamespaceName)

      ' Iterate through the collection to get 
      ' each association end member.
      Dim endMember As AssociationEndMember
      For Each endMember In associationType.AssociationEndMembers
       Console.WriteLine(ControlChars.Tab & _
         " End Name: {0}, Type: {1}, Multiplicity: {2}", _
         endMember.Name, endMember.TypeUsage.EdmType.Name, _
         endMember.RelationshipMultiplicity)
      Next
    Next
  End Sub

  Public Shared Sub GetAssociationSets( _
    ByVal workspace As MetadataWorkspace, ByVal model As DataSpace)

    Console.WriteLine("***Get Association Sets =>")
    ' Get a collection of entity containers.
    Dim containers As ReadOnlyCollection(Of EntityContainer) = _
          workspace.GetItems(Of EntityContainer)(model)
    Dim container As EntityContainer

    ' Iterate through the collection to get each entity container.
    For Each container In containers
       Dim baseSet As EntitySetBase
       ' Iterate through the collection to get each entity set base.
       For Each baseSet In container.BaseEntitySets
         ' EntitySetBase is a super type for 
         ' AssociationSet and EntitySet. 
         ' Check if the current object is an instance of the 
         ' AssociationSet.
         If TypeOf baseSet Is AssociationSet Then
            Console.WriteLine( _
             "AssociationSet Name: {0} , AssociationType Name: {1} ", _
             baseSet.Name, baseSet.ElementType.FullName)

             Dim associationSet As AssociationSet = _
                 TryCast(baseSet, AssociationSet)
             Dim end1 As AssociationSetEnd

             ' Iterate through the collection to get 
             ' each association end.
             For Each end1 In associationSet.AssociationSetEnds
               Console.WriteLine( _
                 "EntitySet Name: {0} , Name: {1}, AssociationEndMember: {2} ", _
                  end1.EntitySet, end1.Name, _
                  end1.CorrespondingAssociationEndMember)
               Next
         End If
      Next
    Next
  End Sub

  Public Shared Sub GetOneAssociationSet( _
    ByVal workspace As MetadataWorkspace, _
    ByVal relationshipName As String, _
    ByVal model As DataSpace)

    Console.WriteLine("***Get One AssociationSet =>")
    ' Get a collection of entity containers.
    Dim containers As ReadOnlyCollection(Of EntityContainer) = _
      workspace.GetItems(Of EntityContainer)(model)
    Dim container As EntityContainer

    ' Iterate through the collection to get each entity container.
    For Each container In containers
       Dim relationshipSet As RelationshipSet
       relationshipSet = Nothing
       ' Check if the relationship with the specified name exists 
       ' or not.
       If container.TryGetRelationshipSetByName( _
          relationshipName, True, relationshipSet) Then
          Dim associationSet As AssociationSet = _
            TryCast(relationshipSet, AssociationSet)
          Console.WriteLine( _
            "AssociationSet Name: {0} , AssociationType Name: {1} ", _
             associationSet.Name, associationSet.ElementType.FullName)
        End If
      Next
  End Sub
End Class

另請參閱

概念

中繼資料型別階層