Cómo: Ejecutar una consulta que devuelve resultados StructuralType (EntityClient)

En este tema se muestra cómo ejecutar un comando en un modelo conceptual usando un objeto EntityCommand, y cómo recuperar los resultados de StructuralType usando un objeto EntityDataReader. Las clases EntityType, RowType y ComplexType se derivan de la clase StructuralType.

Para ejecutar el código de este ejemplo

1. Agregue el Modelo AdventureWorks Sales al proyecto y configúrelo para usar Entity Framework . Para obtener más información, vea Cómo usar el Asistente para Entity Data Model (Entity Framework).

2. En la página de códigos de la aplicación, agregue las siguientes instrucciones using (Imports en Visual Basic):

   Imports System
   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
   

   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;
   

Ejemplo

En este ejemplo se ejecuta una consulta que devuelve resultados EntityType. Si pasa la siguiente consulta como un argumento a la función ExecuteStructuralTypeQuery, la función muestra detalles sobre los Products:

SELECT VALUE Product FROM AdventureWorksEntities.Products AS Product

Si pasa una consulta parametrizada, como la siguiente, agregue los objetos EntityParameter a la propiedad Parameters en el objeto EntityCommand.

SELECT VALUE product FROM AdventureWorksEntities.Products 
    AS product where product.ListPrice >= @price

Private Shared Sub ExecuteStructuralTypeQuery(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()
                    StructuralTypeVisitRecord(TryCast(rdr, IExtendedDataRecord))
                End While
            End Using
        End Using
        conn.Close()
    End Using
End Sub

Private Shared Sub StructuralTypeVisitRecord(ByVal record As IExtendedDataRecord)
    Dim fieldCount As Integer = record.DataRecordInfo.FieldMetadata.Count
    For fieldIndex As Integer = 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();

        // 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);
                }
            }
        }
        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());
            }
        }
    }
}

Vea también

Conceptos

Referencia de Entity SQL
Proveedor de EntityClient para Entity Framework