Ejemplos de sintaxis de consulta basada en métodos: proyección (LINQ to Entities)

Los ejemplos de este tema muestran cómo se utilizan los métodos Select y SelectMany para consultar el modelo AdventureWorks Sales utilizando la sintaxis de las consultas basadas en métodos. El modelo AdventureWorks Sales que se usa en estos ejemplos se crea a partir de las tablas Contact, Address, Product, SalesOrderHeader y SalesOrderDetail en la base de datos de ejemplo de AdventureWorks.

Los ejemplos de este tema usan las siguientes instrucciones using/Imports:

Option Explicit On
Option Strict On
Imports L2EExamplesVB.AdventureWorksModel
Imports System.Data.Objects
Imports System.Globalization

using System;
using System.Data;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Objects;
using AdventureWorksModel;
using System.Globalization;

Para obtener más información, vea Cómo crear un proyecto de LINQ to Entities en Visual Studio.

Select

Ejemplo

En el ejemplo siguiente se utiliza el método Select para proyectar las propiedades Product.Name y Product.ProductID en una secuencia de tipos anónimos.

Using AWEntities As New AdventureWorksEntities
    Dim query = AWEntities.Product _
    .Select(Function(prod) New With _
    { _
        .ProductName = prod.Name, _
        .ProductId = prod.ProductID _
    })

    Console.WriteLine("Product Info:")
    For Each productInfo In query
        Console.WriteLine("Product Id: {0} Product name: {1} ", _
                productInfo.ProductId, productInfo.ProductName)
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    var query = AWEntities.Product
        .Select(product => new
        {
            ProductId = product.ProductID,
            ProductName = product.Name
        });

    Console.WriteLine("Product Info:");
    foreach (var productInfo in query)
    {
        Console.WriteLine("Product Id: {0} Product name: {1} ",
            productInfo.ProductId, productInfo.ProductName);
    }
}

Ejemplo

En el ejemplo siguiente se utiliza el método Select para devolver una secuencia de nombres de producto solamente.

Using AWEntities As New AdventureWorksEntities
    Dim productNames = AWEntities.Product _
    .Select(Function(p) p.Name())

    Console.WriteLine("Product Names:")
    For Each productName In productNames
        Console.WriteLine(productName)
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    IQueryable<string> productNames = AWEntities.Product
        .Select(p => p.Name);

    Console.WriteLine("Product Names:");
    foreach (String productName in productNames)
    {
        Console.WriteLine(productName);
    }
}

SelectMany

Ejemplo

En el ejemplo siguiente se utiliza el método SelectMany para seleccionar todos los pedidos en los que TotalDue es inferior a 500,00.

Using AWEntities As New AdventureWorksEntities
    Dim contacts As ObjectQuery(Of Contact) = AWEntities.Contact
    Dim orders As ObjectQuery(Of SalesOrderHeader) = AWEntities.SalesOrderHeader

    Dim query = contacts.SelectMany( _
        Function(contact) orders.Where(Function(order) _
            (contact.ContactID = order.Contact.ContactID) _
                    And order.TotalDue < 500D) _
            .Select(Function(order) New With _
            { _
                .ContactID = contact.ContactID, _
                .LastName = contact.LastName, _
                .FirstName = contact.FirstName, _
                .OrderID = order.SalesOrderID, _
                .Total = order.TotalDue _
            }) _
    )

    For Each smallOrder In query
        Console.WriteLine("Contact ID: {0} Name: {1}, {2} Order ID: {3} Total Due: ${4} ", _
            smallOrder.ContactID, smallOrder.LastName, smallOrder.FirstName, _
            smallOrder.OrderID, smallOrder.Total)
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    ObjectQuery<Contact> contacts = AWEntities.Contact;
    ObjectQuery<SalesOrderHeader> orders = AWEntities.SalesOrderHeader;

    var query =
    contacts.SelectMany(
        contact => orders.Where(order =>
            (contact.ContactID == order.Contact.ContactID)
                && order.TotalDue < 500.00M)
            .Select(order => new
            {
                ContactID = contact.ContactID,
                LastName = contact.LastName,
                FirstName = contact.FirstName,
                OrderID = order.SalesOrderID,
                Total = order.TotalDue
            }));

    foreach (var smallOrder in query)
    {
        Console.WriteLine("Contact ID: {0} Name: {1}, {2} Order ID: {3} Total Due: ${4} ",
            smallOrder.ContactID, smallOrder.LastName, smallOrder.FirstName,
            smallOrder.OrderID, smallOrder.Total);
    }
}

Ejemplo

En este ejemplo se utiliza el método SelectMany para seleccionar todos los pedidos efectuados a partir del 1 de octubre de 2002.

Using AWEntities As New AdventureWorksEntities
    Dim contacts As ObjectQuery(Of Contact) = AWEntities.Contact
    Dim orders As ObjectQuery(Of SalesOrderHeader) = AWEntities.SalesOrderHeader

    Dim query = contacts.SelectMany( _
        Function(contact) orders.Where(Function(order) _
            (contact.ContactID = order.Contact.ContactID) _
                    And order.OrderDate >= New DateTime(2002, 10, 1)) _
            .Select(Function(order) New With _
            { _
                .ContactID = contact.ContactID, _
                .LastName = contact.LastName, _
                .FirstName = contact.FirstName, _
                .OrderID = order.SalesOrderID, _
                .OrderDate = order.OrderDate _
            }) _
    )

    For Each order In query
        Console.WriteLine("Contact ID: {0} Name: {1}, {2} Order ID: {3} Order date: {4:d} ", _
            order.ContactID, order.LastName, order.FirstName, _
            order.OrderID, order.OrderDate)
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    ObjectQuery<Contact> contacts = AWEntities.Contact;
    ObjectQuery<SalesOrderHeader> orders = AWEntities.SalesOrderHeader;

    var query =
    contacts.SelectMany(
        contact => orders.Where(order =>
            (contact.ContactID == order.Contact.ContactID)
                && order.OrderDate >= new DateTime(2002, 10, 1))
            .Select(order => new
            {
                ContactID = contact.ContactID,
                LastName = contact.LastName,
                FirstName = contact.FirstName,
                OrderID = order.SalesOrderID,
                OrderDate = order.OrderDate
            }));

    foreach (var order in query)
    {
        Console.WriteLine("Contact ID: {0} Name: {1}, {2} Order ID: {3} Order date: {4:d} ",
            order.ContactID, order.LastName, order.FirstName,
            order.OrderID, order.OrderDate);
    }
}

Vea también

Conceptos

Ejemplos de sintaxis de consulta basada en métodos (LINQ to Entities)