Esempi di sintassi di query basate sul metodo: partizionamentoMethod-Based Query Syntax Examples: Partitioning

Negli esempi in questo argomento viene illustrato come utilizzare il Skip, e Take metodi per eseguire una query di modello Sales di AdventureWorks usando la sintassi di espressione di query.The examples in this topic demonstrate how to use the Skip, and Take methods to query the AdventureWorks Sales Model using query expression syntax. Il modello Sales di AdventureWorks usato in questi esempi è compilato in base alle tabelle Contact, Address, Product, SalesOrderHeader e SalesOrderDetail del database di esempio AdventureWorks.The AdventureWorks Sales Model used in these examples is built from the Contact, Address, Product, SalesOrderHeader, and SalesOrderDetail tables in the AdventureWorks sample database.

Gli esempi in questo argomento usano seguenti using / Imports istruzioni:The examples in this topic use the following using/Imports statements:

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

SkipSkip

EsempioExample

Nell'esempio seguente viene usato il metodo Skip per ottenere tutti i contatti della tabella Contact ad eccezione dei primi cinque.The following example uses the Skip method to get all but the first five contacts of the Contact table.

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    // LINQ to Entities only supports Skip on ordered collections.
    IOrderedQueryable<Product> products = context.Products
            .OrderBy(p => p.ListPrice);

    IQueryable<Product> allButFirst3Products = products.Skip(3);

    Console.WriteLine("All but first 3 products:");
    foreach (Product product in allButFirst3Products)
    {
        Console.WriteLine("Name: {0} \t ID: {1}",
            product.Name,
            product.ProductID);
    }
}
Using context As New AdventureWorksEntities
    'LINQ to Entities only supports Skip on ordered collections.
    Dim products As IOrderedQueryable(Of Product) = _
            context.Products.OrderBy(Function(p) p.ListPrice)

    Dim allButFirst3Products As IQueryable(Of Product) = products.Skip(3)

    Console.WriteLine("All but first 3 products:")
    For Each product As Product In allButFirst3Products
        Console.WriteLine("Name: {0} \t ID: {1}", _
                product.Name, _
                product.ProductID)
    Next
End Using

EsempioExample

Nell'esempio seguente viene usato il metodo Skip per ottenere tutti gli indirizzi di Seattle ad eccezione dei primi due.The following example uses the Skip method to get all but the first two addresses in 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: {0} Order ID: {1} Total Due: {2:d}",
            order.City, order.OrderID, order.OrderDate);
    }
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

TakeTake

EsempioExample

Nell'esempio seguente viene usato il metodo Take per ottenere solo i primi cinque contatti della tabella Contact.The following example uses the Take method to get only the first five contacts from the Contact table.

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    IQueryable<Contact> first5Contacts = context.Contacts.Take(5);

    Console.WriteLine("First 5 contacts:");
    foreach (Contact contact in first5Contacts)
    {
        Console.WriteLine("Title = {0} \t FirstName = {1} \t Lastname = {2}",
            contact.Title,
            contact.FirstName,
            contact.LastName);
    }
}
Using context As New AdventureWorksEntities
    Dim contacts As ObjectSet(Of Contact) = context.Contacts

    Dim first5Contacts As IQueryable(Of Contact) = contacts.Take(5)

    Console.WriteLine("First 5 contacts:")
    For Each contact As Contact In first5Contacts
        Console.WriteLine("Title = {0} " & vbTab & " FirstName = {1} " _
            & vbTab & " Lastname = {2}", contact.Title, contact.FirstName, _
            contact.LastName)
    Next
End Using

EsempioExample

Nell'esempio seguente viene usato il metodo Take per ottenere i primi tre indirizzi di Seattle.The following example uses the Take method to get the first three addresses in 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: {0} Order ID: {1} Total Due: {2:d}",
            order.City, order.OrderID, order.OrderDate);
    }
}
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 ancheSee Also

Query in LINQ to EntitiesQueries in LINQ to Entities