Ejemplos de sintaxis de consulta basada en métodos: Particionamiento
Los ejemplos de este tema muestran cómo se utilizan los métodos Skip y Take para consultar el modelo AdventureWorks Sales con la sintaxis de las expresiones de consulta. El modelo AdventureWorks Sales que se usa en estos ejemplos se crea a partir de las tablas Contact, Address, Product, SalesOrderHeader y SalesOrderDetail en la base de datos de ejemplo de AdventureWorks.
Los ejemplos de este tema utilizan las siguientes instrucciones using/Imports:
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
Omitir
Ejemplo
En el ejemplo siguiente se utiliza el método Skip para obtener todos los contactos menos los tres primeros de la tabla Contact.
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
Ejemplo
En el ejemplo siguiente se utiliza el método Skip para obtener las dos primeras direcciones de 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
Take
Ejemplo
En el ejemplo siguiente se utiliza el método Take para obtener únicamente los cinco primeros contactos de la tabla Contact.
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
Ejemplo
En el ejemplo siguiente se utiliza el método Take para obtener las tres primeras direcciones de 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