Esempi di sintassi delle espressioni di query: restrizione (LINQ to Entities)

Negli esempi inclusi in questo argomento viene illustrato come utilizzare il metodo Where per eseguire query sul modello Sales di AdventureWorks utilizzando la sintassi delle espressioni di query. Il modello Sales di AdventureWorks utilizzato in questi esempi è compilato in base alle tabelle Contact, Address, Product, SalesOrderHeader e SalesOrderDetail del database di esempio AdventureWorks.

Negli esempi di questo argomento vengono utilizzate le istruzioni using/Imports seguenti:

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;

Per ulteriori informazioni, vedere Procedura: creare un progetto LINQ to Entities in Visual Studio.

Where

Esempio

Nell'esempio seguente vengono restituiti tutti gli ordini in linea.

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

    Dim onlineOrders = _
        From order In orders _
        Where order.OnlineOrderFlag = True _
        Select New With { _
           .SalesOrderID = order.SalesOrderID, _
           .OrderDate = order.OrderDate, _
           .SalesOrderNumber = order.SalesOrderNumber _
        }

    For Each onlineOrder In onlineOrders
        Console.WriteLine("Order ID: {0} Order date: {1:d} Order number: {2}", _
                onlineOrder.SalesOrderID, _
                onlineOrder.OrderDate, _
                onlineOrder.SalesOrderNumber)
    Next
End Using

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

    var onlineOrders =
        from order in orders
        where order.OnlineOrderFlag == true
        select new
        {
            SalesOrderID = order.SalesOrderID,
            OrderDate = order.OrderDate,
            SalesOrderNumber = order.SalesOrderNumber
        };

    foreach (var onlineOrder in onlineOrders)
    {
        Console.WriteLine("Order ID: {0} Order date: {1:d} Order number: {2}",
            onlineOrder.SalesOrderID,
            onlineOrder.OrderDate,
            onlineOrder.SalesOrderNumber);
    }
}

Esempio

Nell'esempio seguente vengono restituiti gli ordini in cui la quantità ordinata è maggiore di 2 e minore di 6.

Using AWEntities As New AdventureWorksEntities
    Dim orders As ObjectQuery(Of SalesOrderDetail) = AWEntities.SalesOrderDetail

    Dim query = _
        From order In orders _
        Where order.OrderQty > 2 And order.OrderQty < 6 _
        Select New With { _
            .SalesOrderID = order.SalesOrderID, _
            .OrderQty = order.OrderQty _
        }

    For Each order In query
        Console.WriteLine("Order ID: {0} Order quantity: {1}", _
                order.SalesOrderID, order.OrderQty)
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    ObjectQuery<SalesOrderDetail> orders = AWEntities.SalesOrderDetail;

    var query =
        from order in orders
        where order.OrderQty > 2 && order.OrderQty < 6
        select new
        {
            SalesOrderID = order.SalesOrderID,
            OrderQty = order.OrderQty
        };

    foreach (var order in query)
    {
        Console.WriteLine("Order ID: {0} Order quantity: {1}",
            order.SalesOrderID, order.OrderQty);
    }
}

Esempio

Nell'esempio seguente vengono restituiti tutti i prodotti di colore rosso.

Using AWEntities As New AdventureWorksEntities
    Dim products As ObjectQuery(Of Product) = AWEntities.Product

    Dim query = _
        From product In products _
        Where product.Color = "Red" _
        Select New With { _
            .Name = product.Name, _
            .ProductNumber = product.ProductNumber, _
            .ListPrice = product.ListPrice _
        }

    For Each product In query
        Console.WriteLine("Name: {0}", product.Name)
        Console.WriteLine("Product number: {0}", product.ProductNumber)
        Console.WriteLine("List price: ${0}", product.ListPrice)
        Console.WriteLine("")
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    ObjectQuery<Product> products = AWEntities.Product;

    var query =
        from product in products
        where product.Color == "Red"
        select new
        {
            Name = product.Name,
            ProductNumber = product.ProductNumber,
            ListPrice = product.ListPrice
        };

    foreach (var product in query)
    {
        Console.WriteLine("Name: {0}", product.Name);
        Console.WriteLine("Product number: {0}", product.ProductNumber);
        Console.WriteLine("List price: ${0}", product.ListPrice);
        Console.WriteLine("");
    }
}

Esempio

Nell'esempio seguente viene utilizzato il metodo Where per individuare gli ordini effettuati dopo l'1 dicembre 2003, quindi viene utilizzata la proprietà di navigazione order.SalesOrderDetail per ottenere i dettagli relativi a ogni ordine.

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

    Dim query = _
        From order In orders _
        Where order.OrderDate >= New DateTime(2003, 12, 1) _
        Select order

    Console.WriteLine("Orders that were made after December 1, 2003:")
    For Each order In query
        Console.WriteLine("OrderID {0} Order date: {1:d} ", _
                order.SalesOrderID, order.OrderDate)
        For Each orderDetail In order.SalesOrderDetail
            Console.WriteLine("  Product ID: {0} Unit Price {1}", _
                orderDetail.ProductID, orderDetail.UnitPrice)
        Next
    Next
End Using

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

    IQueryable<SalesOrderHeader> query =
        from order in orders
        where order.OrderDate >= new DateTime(2003, 12, 1)
        select order;


    Console.WriteLine("Orders that were made after December 1, 2003:");
    foreach (SalesOrderHeader order in query)
    {
        Console.WriteLine("OrderID {0} Order date: {1:d} ",
            order.SalesOrderID, order.OrderDate);
        foreach (SalesOrderDetail orderDetail in order.SalesOrderDetail)
        {
            Console.WriteLine("  Product ID: {0} Unit Price {1}",
                orderDetail.ProductID, orderDetail.UnitPrice);
        }
    }
}

Vedere anche

Concetti

Esempi di sintassi delle espressioni di query (LINQ to Entities)