Cómo ejecutar una consulta que devuelve resultados StructuralType (EntityClient)

En este tema se proporciona un ejemplo de cómo ejecutar un comando con un Entity Data Model utilizando EntityCommand y cómo recuperar los resultados de StructuralType utilizando EntityDataReader. Los elementos EntityType, RowType y ComplexType se derivan del StructuralType.

Para ejecutar el código de este ejemplo

1. Agregue el modelo AdventureWorks Sales al proyecto y configure el proyecto para utilizar Entity Framework. Para ello, elija entre las siguientes opciones:

   • Si tiene instaladas las herramientas de Entity Dada Model, complete el procedimiento de Cómo usar el Asistente para Entity Data Model (Entity Framework).

   • De lo contrario, complete los procedimientos de Cómo configurar manualmente un proyecto de Entity Framework y Cómo definir manualmente un modelo Entity Data Model (Entity Framework).

2. En la página de códigos de la aplicación, agregue las instrucciones using siguientes (Imports en 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;
   

Ejemplo

Para probar el código, pase la consulta siguiente como argumento a la función ExecuteStructuralTypeQuery:

"SELECT VALUE Product FROM AdventureWorksEntities.Product AS Product"

La consulta anterior devuelve los resultados de 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());
            }
        }
    }
}

Vea también

Conceptos

Referencia de Entity SQL

Otros recursos

Trabajar con EntityClient (tareas de Entity Framework)