Relazioni (metadati)
Le relazioni in Entity Data Model (EDM) definiscono il tipo di correlazione tra due entità. Nell'argomento Relazioni in Entity Data Model vengono fornite informazioni dettagliate sulle relazioni in EDM.
I metadati ADO.NET forniscono un oggetto AssociationType per rappresentare le relazioni tra oggetti EntityType. Un oggetto AssociationType deriva da un oggetto RelationshipType e rappresenta un'associazione EDM. Analogamente, AssociationSet descrive gli oggetti EntitySet che partecipano a un'associazione EDM specifica. Per ulteriori informazioni sui set di entità e di associazioni, vedere Set di entità (EDM) e Set di associazioni (EDM).
Nell'esempio di codice seguente viene illustrato come ottenere un'area di lavoro metadati dalla connessione e quindi utilizzarla per recuperare informazioni sulle relazioni nel modello specificato. Si noti che l'area di lavoro metadati è un componente del servizio di runtime che fornisce supporto per il recupero dei metadati.
Nell'esempio di codice viene utilizzato un oggetto CSpace per specificare il modello. CSpace rappresenta il nome predefinito per il modello concettuale.
L'esempio di codice include tre metodi: GetAssociations, GetAssociationSets e GetOneAssociationSet.
Il metodo GetAssociations ottiene un insieme di associazioni, quindi scorre l'insieme per accedere ai membri End delle associazioni.
Il metodo GetAssociationSets ottiene un insieme di contenitori di entità, quindi scorre l'insieme per ottenere ogni set di associazione nel contenitore specificato. In EDM un oggetto EntityContainer rappresenta un raggruppamento logico di set di entità e set di associazioni. Per ulteriori informazioni sulla definizione dei contenitori di entità in EDM, vedere Contenitori di entità (EDM).
Il metodo GetOneAssociationSet ottiene un insieme di contenitori di entità, quindi scorre l'insieme per ottenere una sola associazione utilizzando il nome specificato.
Nell'esempio di codice seguente viene utilizzato il modello AdventureWorks incluso nell'argomento Modello completo di AdventureWorks (EDM). Per un esempio del file di configurazione dell'applicazione, vedere Utilizzo del modello a oggetti di AdventureWorks (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