关系（元数据）
实体数据模型 (EDM) 中的关系定义两个实体相关的方式。实体数据模型关系主题详细介绍有关 EDM 中的关系的信息。
ADO.NET 元数据提供 AssociationType 来表示各个 EntityType 之间的关系。AssociationType 派生自 RelationshipType 并表示一种 EDM 关联。同样，AssociationSet 描述参与特定 EDM 关联的 EntitySet。有关实体集和关联集的更多信息，请参见实体集 (EDM) 和关联集 (EDM)。
以下代码示例演示如何通过连接获得元数据工作区，然后使用该元数据工作区以在指定模型中检索有关关系的信息。请注意，元数据工作区是一个为检索元数据提供支持的运行时服务组件。
该代码示例使用 CSpace 指定模型。CSpace 表示概念性模型的默认名称。
此代码示例包含三个方法：GetAssociations、GetAssociationSets 和 GetOneAssociationSet。
GetAssociations 方法获取关联集合，然后循环访问此集合以访问其关联 End 成员。
GetAssociationSets 方法获得实体容器的集合，然后循环访问此集合以获取指定容器中的每个关联集。在 EDM 中，EntityContainer 表示实体集和关联集的逻辑分组。有关如何在 EDM 中定义实体容器的更多信息，请参见实体容器 (EDM)。
GetOneAssociationSet 方法获得实体容器的集合，然后循环访问此集合以仅获取使用指定名称的一个关联集。
以下代码示例使用在 AdventureWorks 完整模型 (EDM) 中提供的 Adventureworks 模型。有关应用程序配置文件的示例，请参见使用 AdventureWorks 对象模型 (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