Procedura: eseguire una query che restituisce risultati StructuralType (EntityClient)

In questo argomento viene fornito un esempio per illustrare l'esecuzione di un comando su un modello EDM (Entity Data Model) mediante EntityCommand nonché il recupero dei risultati StructuralType mediante EntityDataReader. EntityType, RowType e ComplexType derivano da StructuralType.

Per eseguire il codice in questo esempio

1. Aggiungere il modello Sales di Adventure Works al progetto e configurare il progetto per l'utilizzo di Entity Framework. A tale scopo, eseguire una delle operazioni seguenti:

   • Se gli strumenti EDM (Entity Dati Model) sono stati installati, completare la procedura descritta in Procedura: utilizzare la procedura guidata Entity Data Model (Entity Framework).

   • In caso contrario, completare le procedure descritte in Procedura: configurare manualmente un progetto di Entity Framework e in Procedura: definire manualmente un modello EDM (Entity Framework).

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

   Imports System
   Imports System.Collections.Generic
   Imports System.Collections
   Imports System.Data.Common
   Imports System.Data
   Imports System.Data.SqlClient
   Imports System.Data.EntityClient
   Imports System.Data.Metadata.Edm
   Imports System.IO
   ' Add AdventureWorksModel prepended with the root namespace for the project.
   'Imports ProjectName.AdventureWorksModel
   

   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 AdventureWorksModel;
   using System.Data.Metadata.Edm;
   

Esempio

Per testare il codice, passare la query seguente come argomento alla funzione ExecuteStructuralTypeQuery:

"SELECT VALUE Product FROM AdventureWorksEntities.Product AS Product"

La query precedente restituisce i risultati EntityType.

Sub ExecuteStructuralTypeQuery(ByVal esqlQuery As String)
    If (esqlQuery.Length = 0) Then
        Console.WriteLine("The query string is empty.")
        Return
    End If


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

        Try
            ' Create an EntityCommand.
            Using cmd As EntityCommand = conn.CreateCommand()
                cmd.CommandText = esqlQuery
                ' Execute the command.
                Using reader As EntityDataReader = cmd.ExecuteReader(CommandBehavior.SequentialAccess)
                    Do While (reader.Read())
                        StructuralTypeVisitRecord(CType(reader, IExtendedDataRecord))
                    Loop
                End Using
            End Using
        Catch ex As Exception
            Console.WriteLine(ex.ToString())
        End Try
        conn.Close()
    End Using
End Sub

Sub StructuralTypeVisitRecord(ByVal record As IExtendedDataRecord)
    Dim fieldCount As Integer
    fieldCount = record.DataRecordInfo.FieldMetadata.Count
    Dim fieldIndex As Integer
    For fieldIndex = 0 To fieldCount - 1
        Console.Write(record.GetName(fieldIndex) + ": ")

        ' 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()
            ' The EntityType, ComplexType and RowType are structural types
            ' that have members. 
            ' Read only the PrimitiveType members of this structural type.
            If (fieldTypeKind = BuiltInTypeKind.PrimitiveType) Then
                ' Primitive types are surfaced as plain objects.
                Console.WriteLine(record.GetValue(fieldIndex).ToString())
            End If
        End If
    Next
End Sub

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

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

        try
        {
            // 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())
                    {
                        StructuralTypeVisitRecord(rdr as IExtendedDataRecord);
                    }
                }
            }
        }
        catch (EntityException ex)
        {
            Console.WriteLine(ex.ToString());
        }
        conn.Close();
    }
}

static void StructuralTypeVisitRecord(IExtendedDataRecord record)
{
    int fieldCount = record.DataRecordInfo.FieldMetadata.Count;
    for (int fieldIndex = 0; fieldIndex < fieldCount; fieldIndex++)
    {
        Console.Write(record.GetName(fieldIndex) + ": ");

        // 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;
            // The EntityType, ComplexType and RowType are structural types
            // that have members. 
            // Read only the PrimitiveType members of this structural type.
            if (fieldTypeKind == BuiltInTypeKind.PrimitiveType)
            {
                // Primitive types are surfaced as plain objects.
                Console.WriteLine(record.GetValue(fieldIndex).ToString());
            }
        }
    }
}

Vedere anche

Concetti

Riferimenti a Entity SQL

Altre risorse

Utilizzo di EntityClient (attività di Entity Framework)