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Procedura: eseguire una query che restituisce risultati RefType

  • Articolo

In questo argomento viene illustrato come eseguire un comando su un modello concettuale usando un oggetto EntityCommand e viene mostrato come recuperare i risultati di RefType usando un oggetto EntityDataReader.

Per eseguire il codice in questo esempio

  1. Aggiungere il modello Sales di AdventureWorks al progetto e configurare il progetto per l'utilizzo di Entity Framework. Per altre informazioni, vedere Procedura: Usare la procedura guidata di Entity Data Model.

  2. Nella tabella codici per l'applicazione aggiungere le istruzioni using seguenti (Imports in Visual Basic):

    using System;
using System.Collections.Generic;
using System.Collections;
using System.Data.Common;
using System.Data;
using System.IO;
using System.Data.SqlClient;
using System.Data.EntityClient;
using System.Data.Metadata.Edm;

    Imports System.Collections.Generic
Imports System.Collections
Imports System.Data.Common
Imports System.Data
Imports System.IO
Imports System.Data.SqlClient
Imports System.Data.EntityClient
Imports System.Data.Metadata.Edm

Esempio

In questo esempio viene eseguita una query che restituisce risultati dell'oggetto RefType. Se si passa la query seguente come argomento alla funzione ExecuteRefTypeQuery, viene restituito un riferimento all'entità:

SELECT REF(p) FROM AdventureWorksEntities.Products as p

Se si passa una query con parametri, come quella riportata di seguito, aggiungere gli oggetti EntityParameter alla proprietà Parameters nell'oggetto EntityCommand.

SELECT REF(p) FROM AdventureWorksEntities.Products as p WHERE p.ProductID == @productID

static public void ExecuteRefTypeQuery(string esqlQuery)
{
    if (esqlQuery.Length == 0)
    {
        Console.WriteLine("The query string is empty.");
        return;
    }

    using (EntityConnection conn =
        new EntityConnection("name=AdventureWorksEntities"))
    {
        conn.Open();

        // Create an EntityCommand.
        using (EntityCommand cmd = conn.CreateCommand())
        {
            cmd.CommandText = esqlQuery;
            // Execute the command.
            using (EntityDataReader rdr =
                cmd.ExecuteReader(CommandBehavior.SequentialAccess))
            {
                // Start reading results.
                while (rdr.Read())
                {
                    RefTypeVisitRecord(rdr as IExtendedDataRecord);
                }
            }
        }
        conn.Close();
    }
}

static void RefTypeVisitRecord(IExtendedDataRecord record)
{
    // For RefType the record contains exactly one field.
    int fieldIndex = 0;

    // If the field is flagged as DbNull, the shape of the value is undetermined.
    // An attempt to get such a value may trigger an exception.
    if (record.IsDBNull(fieldIndex) == false)
    {
        BuiltInTypeKind fieldTypeKind = record.DataRecordInfo.FieldMetadata[fieldIndex].
            FieldType.TypeUsage.EdmType.BuiltInTypeKind;
        //read only fields that contain PrimitiveType
        if (fieldTypeKind == BuiltInTypeKind.RefType)
        {
            // Ref types are surfaced as EntityKey instances.
            // The containing record sees them as atomic.
            EntityKey key = record.GetValue(fieldIndex) as EntityKey;
            // Get the EntitySet name.
            Console.WriteLine("EntitySetName " + key.EntitySetName);
            // Get the Name and the Value information of the EntityKey.
            foreach (EntityKeyMember keyMember in key.EntityKeyValues)
            {
                Console.WriteLine("   Key Name: " + keyMember.Key);
                Console.WriteLine("   Key Value: " + keyMember.Value);
            }
        }
    }
}

Private Shared Sub ExecuteRefTypeQuery(ByVal esqlQuery As String)
    If esqlQuery.Length = 0 Then
        Console.WriteLine("The query string is empty.")
        Exit Sub
    End If

    Using conn As New EntityConnection("name=AdventureWorksEntities")
        conn.Open()

        ' Create an EntityCommand. 
        Using cmd As EntityCommand = conn.CreateCommand()
            cmd.CommandText = esqlQuery
            ' Execute the command. 
            Using rdr As EntityDataReader = cmd.ExecuteReader(CommandBehavior.SequentialAccess)
                ' Start reading results. 
                While rdr.Read()
                    RefTypeVisitRecord(TryCast(rdr, IExtendedDataRecord))
                End While
            End Using
        End Using
        conn.Close()
    End Using
End Sub

Private Shared Sub RefTypeVisitRecord(ByVal record As IExtendedDataRecord)
    ' For RefType the record contains exactly one field. 
    Dim fieldIndex As Integer = 0

    ' If the field is flagged as DbNull, the shape of the value is undetermined. 
    ' An attempt to get such a value may trigger an exception. 
    If record.IsDBNull(fieldIndex) = False Then
        Dim fieldTypeKind As BuiltInTypeKind = record.DataRecordInfo.FieldMetadata(fieldIndex).FieldType.TypeUsage.EdmType.BuiltInTypeKind
        'read only fields that contain PrimitiveType 
        If fieldTypeKind = BuiltInTypeKind.RefType Then
            ' Ref types are surfaced as EntityKey instances. 
            ' The containing record sees them as atomic. 
            Dim key As EntityKey = TryCast(record.GetValue(fieldIndex), EntityKey)
            ' Get the EntitySet name. 
            Console.WriteLine("EntitySetName " & key.EntitySetName)
            ' Get the Name and the Value information of the EntityKey. 
            For Each keyMember As EntityKeyMember In key.EntityKeyValues
                Console.WriteLine(" Key Name: " & keyMember.Key)
                Console.WriteLine(" Key Value: " & keyMember.Value)
            Next
        End If
    End If
End Sub

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