Method-Based Query Syntax Examples: Partitioning (LINQ
Les exemples de cette rubrique montrent comment utiliser les méthodes Skip, SkipWhile, Take et TakeWhile pour interroger un DataSet à l'aide de la syntaxe d'expression de requête.
La méthode FillDataSet utilisée dans ces exemples est spécifiée dans Chargement de données dans un Jeu de données.
Les exemples de cette rubrique utilisent les 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.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Globalization;
using System.Linq;
using System.Windows.Forms;
Option Explicit On
Imports System.Linq
Imports System.Linq.Expressions
Imports System.Collections.Generic
Imports System.Data
Imports System.Data.SqlClient
Imports System.Data.Common
Imports System.Globalization
Pour plus d’informations, consultez Guide pratique pour créer un projet LINQ to DataSet dans Visual Studio.
Ignorer
Exemple
Cet exemple utilise la méthode Skip pour obtenir tous les contacts de la table Contact, à l'exception des cinq premiers.
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable contacts = ds.Tables["Contact"];
IEnumerable<DataRow> allButFirst5Contacts = contacts.AsEnumerable().Skip(5);
Console.WriteLine("All but first 5 contacts:");
foreach (DataRow contact in allButFirst5Contacts)
{
Console.WriteLine("FirstName = {0} \tLastname = {1}",
contact.Field<string>("FirstName"),
contact.Field<string>("Lastname"));
}
' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)
Dim contacts As DataTable = ds.Tables("Contact")
Dim allButFirst5Contacts = contacts.AsEnumerable().Skip(5)
Console.WriteLine("All but first 5 contacts:")
For Each contact In allButFirst5Contacts
Console.Write("FirstName = {0} ", contact.Field(Of String)("FirstName"))
Console.WriteLine(vbTab & " LastName = " & contact.Field(Of String)("LastName"))
Next
Exemple
Cet exemple utilise la méthode Skip pour obtenir toutes les adresses de Seattle, à l'exception des deux premières.
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable addresses = ds.Tables["Address"];
DataTable orders = ds.Tables["SalesOrderHeader"];
var query = (
from address in addresses.AsEnumerable()
from order in orders.AsEnumerable()
where address.Field<int>("AddressID") == order.Field<int>("BillToAddressID")
&& address.Field<string>("City") == "Seattle"
select new
{
City = address.Field<string>("City"),
OrderID = order.Field<int>("SalesOrderID"),
OrderDate = order.Field<DateTime>("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);
}
' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)
Dim addresses As DataTable = ds.Tables("Address")
Dim orders As DataTable = ds.Tables("SalesOrderHeader")
Dim query = ( _
From address In addresses.AsEnumerable() _
From order In orders.AsEnumerable() _
Where (address.Field(Of Integer)("AddressID") = _
order.Field(Of Integer)("BillToAddressID")) _
And address.Field(Of String)("City") = "Seattle" _
Select New With _
{ _
.City = address.Field(Of String)("City"), _
.OrderID = order.Field(Of Integer)("SalesOrderID"), _
.OrderDate = order.Field(Of DateTime)("OrderDate") _
}).Skip(2)
Console.WriteLine("All but first 2 orders in Seattle:")
For Each addOrder In query
Console.Write("City: " & addOrder.City)
Console.Write(" Order ID: " & addOrder.OrderID)
Console.WriteLine(" Order date: " & addOrder.OrderDate)
Next
SkipWhile
Exemple
Cet exemple utilise les méthodes OrderBy et SkipWhile pour retourner des produits de la table Product dont le prix courant est supérieur à 300.
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable products = ds.Tables["Product"];
IEnumerable<DataRow> skipWhilePriceLessThan300 =
products.AsEnumerable()
.OrderBy(listprice => listprice.Field<decimal>("ListPrice"))
.SkipWhile(product => product.Field<decimal>("ListPrice") < 300.00M);
Console.WriteLine("Skip while ListPrice is less than 300.00:");
foreach (DataRow product in skipWhilePriceLessThan300)
{
Console.WriteLine(product.Field<decimal>("ListPrice"));
}
' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)
Dim products As DataTable = ds.Tables("Product")
Dim skipWhilePriceLessThan300 As IEnumerable(Of DataRow) = _
products.AsEnumerable() _
.OrderBy(Function(listprice) listprice.Field(Of Decimal)("ListPrice")) _
.SkipWhile(Function(product) product.Field(Of Decimal)("ListPrice") < 300D)
Console.WriteLine("First ListPrice less than 300.00:")
For Each product As DataRow In skipWhilePriceLessThan300
Console.WriteLine(product.Field(Of Decimal)("ListPrice"))
Next
Take
Exemple
Cet exemple utilise la méthode Take pour obtenir uniquement les cinq premiers contacts de la table Contact.
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable contacts = ds.Tables["Contact"];
IEnumerable<DataRow> first5Contacts = contacts.AsEnumerable().Take(5);
Console.WriteLine("First 5 contacts:");
foreach (DataRow contact in first5Contacts)
{
Console.WriteLine("Title = {0} \t FirstName = {1} \t Lastname = {2}",
contact.Field<string>("Title"),
contact.Field<string>("FirstName"),
contact.Field<string>("Lastname"));
}
' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)
Dim contacts As DataTable = ds.Tables("Contact")
Dim first5Contacts = contacts.AsEnumerable().Take(5)
Console.WriteLine("First 5 contacts:")
For Each contact In first5Contacts
Console.Write("Title = " & contact.Field(Of String)("Title"))
Console.Write(vbTab & "FirstName = " & contact.Field(Of String)("FirstName"))
Console.WriteLine(vbTab & "LastName = " & contact.Field(Of String)("LastName"))
Next
Exemple
Cet exemple utilise la méthode Take pour obtenir les trois premières adresses de Seattle.
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable addresses = ds.Tables["Address"];
DataTable orders = ds.Tables["SalesOrderHeader"];
var query = (
from address in addresses.AsEnumerable()
from order in orders.AsEnumerable()
where address.Field<int>("AddressID") == order.Field<int>("BillToAddressID")
&& address.Field<string>("City") == "Seattle"
select new
{
City = address.Field<string>("City"),
OrderID = order.Field<int>("SalesOrderID"),
OrderDate = order.Field<DateTime>("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);
}
' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)
Dim addresses As DataTable = ds.Tables("Address")
Dim orders As DataTable = ds.Tables("SalesOrderHeader")
Dim query = ( _
From address In addresses.AsEnumerable() _
From order In orders.AsEnumerable() _
Where (address.Field(Of Integer)("AddressID") = _
order.Field(Of Integer)("BillToAddressID")) _
And address.Field(Of String)("City") = "Seattle" _
Select New With _
{ _
.City = address.Field(Of String)("City"), _
.OrderID = order.Field(Of Integer)("SalesOrderID"), _
.OrderDate = order.Field(Of DateTime)("OrderDate") _
}).Take(3)
Console.WriteLine("First 3 orders in Seattle:")
For Each order In query
Console.Write("City: " & order.City)
Console.Write(" Order ID: " & order.OrderID)
Console.WriteLine(" Order date: " & order.OrderDate)
Next
TakeWhile
Exemple
Cet exemple utilise les méthodes OrderBy et TakeWhile pour retourner des produits de la table Product dont le prix courant est inférieur à 300.
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable products = ds.Tables["Product"];
IEnumerable<DataRow> takeWhileListPriceLessThan300 =
products.AsEnumerable()
.OrderBy(listprice => listprice.Field<decimal>("ListPrice"))
.TakeWhile(product => product.Field<decimal>("ListPrice") < 300.00M);
Console.WriteLine("First ListPrice less than 300:");
foreach (DataRow product in takeWhileListPriceLessThan300)
{
Console.WriteLine(product.Field<decimal>("ListPrice"));
}
' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)
Dim products As DataTable = ds.Tables("Product")
Dim takeWhileListPriceLessThan300 As IEnumerable(Of DataRow) = _
products.AsEnumerable() _
.OrderBy(Function(listprice) listprice.Field(Of Decimal)("ListPrice")) _
.TakeWhile(Function(product) product.Field(Of Decimal)("ListPrice") < 300D)
Console.WriteLine("First ListPrice less than 300.00:")
For Each product As DataRow In takeWhileListPriceLessThan300
Console.WriteLine(product.Field(Of Decimal)("ListPrice"))
Next