Voorbeelden van op methoden gebaseerde querysyntaxis: Projectie
De voorbeelden in dit onderwerp laten zien hoe u de Select en SelectMany methoden kunt gebruiken om query's uit te voeren op het AdventureWorks Sales Model met behulp van op methoden gebaseerde querysyntaxis. Het AdventureWorks Sales Model dat in deze voorbeelden wordt gebruikt, is gebaseerd op de tabellen Contact, Adres, Product, SalesOrderHeader en SalesOrderDetail in de voorbeelddatabase AdventureWorks.
In de voorbeelden in dit onderwerp worden de volgende using/Imports instructies gebruikt:
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
Select
Opmerking
In het volgende voorbeeld wordt de Select methode gebruikt om de Product.Name en Product.ProductID eigenschappen te projecteren in een reeks anonieme typen.
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
var query = context.Products
.Select(product => 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 query = context.Products _
.Select(Function(prod) New With _
{ _
.ProductName = prod.Name, _
.ProductId = prod.ProductID _
})
Console.WriteLine("Product Info:")
For Each productInfo In query
Console.WriteLine("Product Id: {0} Product name: {1} ", _
productInfo.ProductId, productInfo.ProductName)
Next
End Using
Opmerking
In het volgende voorbeeld wordt de Select methode gebruikt om een reeks alleen productnamen te retourneren.
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
IQueryable<string> productNames = context.Products
.Select(p => p.Name);
Console.WriteLine("Product Names:");
foreach (String productName in productNames)
{
Console.WriteLine(productName);
}
}
Using context As New AdventureWorksEntities
Dim productNames = context.Products _
.Select(Function(p) p.Name())
Console.WriteLine("Product Names:")
For Each productName In productNames
Console.WriteLine(productName)
Next
End Using
SelectMany
Opmerking
In het volgende voorbeeld wordt de SelectMany methode gebruikt om alle orders te selecteren waarvoor TotalDue minder dan 500,00 is.
decimal totalDue = 500.00M;
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
ObjectSet<Contact> contacts = context.Contacts;
ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;
var query =
contacts.SelectMany(
contact => orders.Where(order =>
(contact.ContactID == order.Contact.ContactID)
&& order.TotalDue < totalDue)
.Select(order => 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 = contacts.SelectMany( _
Function(contact) orders.Where(Function(order) _
(contact.ContactID = order.Contact.ContactID) _
And order.TotalDue < totalDue) _
.Select(Function(order) 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
Opmerking
In het volgende voorbeeld wordt de SelectMany methode gebruikt om alle orders te selecteren waarin de bestelling is gemaakt op 1 oktober 2002 of hoger.
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
ObjectSet<Contact> contacts = context.Contacts;
ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;
var query =
contacts.SelectMany(
contact => orders.Where(order =>
(contact.ContactID == order.Contact.ContactID)
&& order.OrderDate >= new DateTime(2002, 10, 1))
.Select(order => 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 = contacts.SelectMany( _
Function(contact) orders.Where(Function(order) _
(contact.ContactID = order.Contact.ContactID) _
And order.OrderDate >= New DateTime(2002, 10, 1)) _
.Select(Function(order) 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