Beispiele für die methodenbasierte Abfragesyntax: Partitionierung
In diesem Thema wird anhand von Beispielen gezeigt, wie Sie mithilfe der Methoden Skip und Take das AdventureWorks Sales-Modell unter Verwendung der Abfrageausdruckssyntax abfragen. Für das in den Beispielen verwendete "AdventureWorks Sales"-Modell wurde auf die Tabellen Contact, Address, Product, SalesOrderHeader und SalesOrderDetail der "AdventureWorks"-Beispieldatenbank zurückgegriffen.
Die Beispiele in diesem Thema beziehen sich auf die folgenden using/Imports-Anweisungen:
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
Überspringen
Beispiel
Im folgenden Beispiel wird die Skip-Methode verwendet, um, mit Ausnahme der ersten drei Kontakte, alle Kontakte der Contact-Tabelle abzurufen.
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
Beispiel
Im folgenden Beispiel wird die Skip-Methode verwendet, um, mit Ausnahme der ersten beiden Adressen, alle Adressen in Seattle abzurufen.
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
Take
Beispiel
Im folgenden Beispiel wird die -Methode verwendet, um nur die ersten fünf Kontakte aus der Contact-Tabelle abzurufen.
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
Beispiel
Im folgenden Beispiel wird die Take-Methode verwendet, um die ersten drei Adressen in Seattle abzurufen.
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