Exemples de syntaxe d'expression de requête : Projection
Les exemples fournis dans cette rubrique montrent comment utiliser la méthode Select et les mots clés From … From … pour interroger le modèle de vente AdventureWorks Sales Model à l’aide de la syntaxe d’expression de requête. From … From … est l'équivalent basé sur une requête de la méthode SelectMany. 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 :
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
Sélectionnez
Exemple
L'exemple ci-dessous utilise la méthode Select pour retourner toutes les lignes de la table Product et afficher les noms de produits.
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
IQueryable<Product> productsQuery = from product in context.Products
select product;
Console.WriteLine("Product Names:");
foreach (var prod in productsQuery)
{
Console.WriteLine(prod.Name);
}
}
Using context As New AdventureWorksEntities
Dim products As ObjectSet(Of Product) = context.Products
Dim productsQuery = _
From product In products _
Select product
Console.WriteLine("Product Names:")
For Each product In productsQuery
Console.WriteLine(product.Name)
Next
End Using
Exemple
L'exemple ci-dessous utilise Select pour retourner une séquence comportant uniquement des noms de produits.
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
IQueryable<string> productNames =
from p in context.Products
select p.Name;
Console.WriteLine("Product Names:");
foreach (String productName in productNames)
{
Console.WriteLine(productName);
}
}
Using context As New AdventureWorksEntities
Dim products As ObjectSet(Of Product) = context.Products
Dim productNames = _
From p In products _
Select p.Name
Console.WriteLine("Product Names:")
For Each productName In productNames
Console.WriteLine(productName)
Next
End Using
Exemple
L'exemple ci-dessous utilise la méthode Select pour projeter les propriétés Product.Name et Product.ProductID dans une séquence de types anonymes.
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
var query =
from product in context.Products
select 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);
}
}
Using context As New AdventureWorksEntities
Dim products As ObjectSet(Of Product) = context.Products
Dim query = _
From product In products _
Select New With _
{ _
.ProductId = product.ProductID, _
.ProductName = product.Name _
}
Console.WriteLine("Product Info:")
For Each productInfo In query
Console.WriteLine("Product Id: {0} Product name: {1} ", _
productInfo.ProductId, productInfo.ProductName)
Next
End Using
From … From … (SelectMany)
Exemple
L'exemple ci-dessous utilise From … From … (l'équivalent de la méthode SelectMany) pour sélectionner toutes les commandes où TotalDue est inférieur à 500.
decimal totalDue = 500.00M;
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
ObjectSet<Contact> contacts = context.Contacts;
ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;
var query =
from contact in contacts
from order in orders
where contact.ContactID == order.Contact.ContactID
&& order.TotalDue < totalDue
select 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);
}
}
Dim totalDue = 500D
Using context As New AdventureWorksEntities
Dim contacts As ObjectSet(Of Contact) = context.Contacts
Dim orders As ObjectSet(Of SalesOrderHeader) = context.SalesOrderHeaders
Dim query = _
From contact In contacts _
From order In orders _
Where contact.ContactID = order.Contact.ContactID _
And order.TotalDue < totalDue _
Select 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
Exemple
L'exemple ci-dessous utilise From … From … (l'équivalent de la méthode SelectMany) pour sélectionner toutes les commandes qui ont été passées le 1er octobre 2002 ou après.
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
ObjectSet<Contact> contacts = context.Contacts;
ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;
var query =
from contact in contacts
from order in orders
where contact.ContactID == order.Contact.ContactID
&& order.OrderDate >= new DateTime(2002, 10, 1)
select 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);
}
}
Using context As New AdventureWorksEntities
Dim contacts As ObjectSet(Of Contact) = context.Contacts
Dim orders As ObjectSet(Of SalesOrderHeader) = context.SalesOrderHeaders
Dim query = _
From contact In contacts _
From order In orders _
Where contact.ContactID = order.Contact.ContactID _
And order.OrderDate >= New DateTime(2002, 10, 1) _
Select 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
Exemple
L'exemple ci-dessous utilise From … From … (l'équivalent de la méthode SelectMany) pour sélectionner toutes les commandes dont le total est supérieur à 10 000 et utilise l'assignation From pour éviter de demander deux fois le total.
decimal totalDue = 10000.0M;
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
ObjectSet<Contact> contacts = context.Contacts;
ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;
var query =
from contact in contacts
from order in orders
let total = order.TotalDue
where contact.ContactID == order.Contact.ContactID
&& total >= totalDue
select new
{
ContactID = contact.ContactID,
LastName = contact.LastName,
OrderID = order.SalesOrderID,
total
};
foreach (var order in query)
{
Console.WriteLine("Contact ID: {0} Last name: {1} Order ID: {2} Total: {3}",
order.ContactID, order.LastName, order.OrderID, order.total);
}
}
Dim totalDue = 10000D
Using context As New AdventureWorksEntities
Dim contacts As ObjectSet(Of Contact) = context.Contacts
Dim orders As ObjectSet(Of SalesOrderHeader) = context.SalesOrderHeaders
Dim query = _
From contact In contacts _
From order In orders _
Let total = order.TotalDue _
Where contact.ContactID = order.Contact.ContactID _
And total >= totalDue _
Select New With _
{ _
.ContactID = contact.ContactID, _
.LastName = contact.LastName, _
.OrderID = order.SalesOrderID, _
total _
}
For Each order In query
Console.WriteLine("Contact ID: {0} Last name: {1} Order ID: {2} Total: {3}", _
order.ContactID, order.LastName, order.OrderID, order.total)
Next
End Using