Esempi di sintassi delle espressioni di query: partizionamento

Negli esempi di questo argomento viene illustrato come usare i metodi Skip e Take per eseguire query sul modello di vendita AdventureWorks usando la sintassi delle espressioni di query. Il modello Di vendita AdventureWorks usato in questi esempi è basato sulle tabelle Contact, Address, Product, SalesOrderHeader e SalesOrderDetail nel database di esempio AdventureWorks.

Gli esempi in questo argomento usano le istruzioni using/Imports seguenti:

using System;
using System.Data;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Objects;
using System.Globalization;
using System.Data.EntityClient;
using System.Data.SqlClient;
using System.Data.Common;

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

Salta

Esempio

Nell'esempio seguente viene usato il metodo Skip per ottenere tutti gli indirizzi esclusi i primi due a Seattle.

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Address> addresses = context.Addresses;
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    //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: {order.City} Order ID: {order.OrderID} Total Due: {order.OrderDate:d}");
    }

Using context As New AdventureWorksEntities
    Dim orders As ObjectSet(Of SalesOrderHeader) = context.SalesOrderHeaders
    Dim addresses As ObjectSet(Of Address) = context.Addresses

    '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

Prendere

Esempio

Nell'esempio seguente viene usato il metodo Take per ottenere i primi tre indirizzi di Seattle.

String city = "Seattle";
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Address> addresses = context.Addresses;
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    var query = (
        from address in addresses
        from order in orders
        where address.AddressID == order.Address.AddressID
             && address.City == city
        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: {order.City} Order ID: {order.OrderID} Total Due: {order.OrderDate:d}");
    }
}

Dim city = "Seattle"
Using context As New AdventureWorksEntities
    Dim orders As ObjectSet(Of SalesOrderHeader) = context.SalesOrderHeaders
    Dim addresses As ObjectSet(Of Address) = context.Addresses

    Dim query = ( _
        From address In addresses _
        From order In orders _
        Where address.AddressID = order.Address.AddressID _
                 And address.City = city _
        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

Vedere anche

• Interrogazioni in LINQ to Entities