Exemples de syntaxe d'expression de requête : partitionnement (LINQ to Entities)

Les exemples de cette rubrique montrent comment utiliser les méthodes Skip et Take pour interroger le modèle de vente AdventureWorks Sales Model à l'aide de la syntaxe d'expression de requête. Le modèle de vente AdventureWorks Sales Model utilisé dans ces exemples est construit à partir des tables Contact, Address, Product, SalesOrderHeader et SalesOrderDetail de l'exemple de base de données AdventureWorks.

Les exemples de cette rubrique utilisent les instructions using/Imports suivantes :

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;

Pour plus d'informations, voir Procédure : créer un projet LINQ to Entities dans Visual Studio.

Skip

Exemple

L'exemple suivant utilise la méthode Skip pour obtenir toutes les adresses de Seattle, à l'exception des deux premières.

Using AWEntities As New AdventureWorksEntities
    Dim orders As ObjectQuery(Of SalesOrderHeader) = AWEntities.SalesOrderHeader
    Dim addresses As ObjectQuery(Of Address) = AWEntities.Address

    'LINQ to Entities only supports Skip on ordered collections.
    Dim query = ( _
        From address In addresses _
        From order In orders _
        Where address.AddressID = order.Address.AddressID _
                 And address.City = "Seattle" _
        Order By order.SalesOrderID _
        Select New With _
        { _
            .City = address.City, _
            .OrderID = order.SalesOrderID, _
            .OrderDate = order.OrderDate _
        }).Skip(2)

    Console.WriteLine("All but first 2 orders in Seattle:")
    For Each order In query
        Console.WriteLine("City: {0} Order ID: {1} Total Due: {2:d}", _
            order.City, order.OrderID, order.OrderDate)
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    ObjectQuery<Address> addresses = AWEntities.Address;
    ObjectQuery<SalesOrderHeader> orders = AWEntities.SalesOrderHeader;

    //LINQ to Entities only supports Skip on ordered collections.
    var query = (
        from address in addresses
        from order in orders
        where address.AddressID == order.Address.AddressID
             && address.City == "Seattle"
        orderby order.SalesOrderID
        select new
        {
            City = address.City,
            OrderID = order.SalesOrderID,
            OrderDate = order.OrderDate
        }).Skip(2);

    Console.WriteLine("All but first 2 orders in Seattle:");
    foreach (var order in query)
    {
        Console.WriteLine("City: {0} Order ID: {1} Total Due: {2:d}",
            order.City, order.OrderID, order.OrderDate);
    }

Take

Exemple

L'exemple suivant utilise la méthode Take pour obtenir les trois premières adresses de Seattle.

Using AWEntities As New AdventureWorksEntities
    Dim orders As ObjectQuery(Of SalesOrderHeader) = AWEntities.SalesOrderHeader
    Dim addresses As ObjectQuery(Of Address) = AWEntities.Address

    Dim query = ( _
        From address In addresses _
        From order In orders _
        Where address.AddressID = order.Address.AddressID _
                 And address.City = "Seattle" _
        Select New With _
        { _
            .City = address.City, _
            .OrderID = order.SalesOrderID, _
            .OrderDate = order.OrderDate _
        }).Take(3)

    Console.WriteLine("First 3 orders in Seattle:")
    For Each order In query
        Console.WriteLine("City: {0} Order ID: {1} Total Due: {2:d}", _
            order.City, order.OrderID, order.OrderDate)
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    ObjectQuery<Address> addresses = AWEntities.Address;
    ObjectQuery<SalesOrderHeader> orders = AWEntities.SalesOrderHeader;

    var query = (
        from address in addresses
        from order in orders
        where address.AddressID == order.Address.AddressID
             && address.City == "Seattle"
        select new
        {
            City = address.City,
            OrderID = order.SalesOrderID,
            OrderDate = order.OrderDate
        }).Take(3);
    Console.WriteLine("First 3 orders in Seattle:");
    foreach (var order in query)
    {
        Console.WriteLine("City: {0} Order ID: {1} Total Due: {2:d}",
            order.City, order.OrderID, order.OrderDate);
    }
}

Voir aussi

Concepts

Exemples de syntaxe d'expression de requête (LINQ to Entities)