Esempi di sintassi di espressione di query: partizionamento (LINQ to DataSet)
Negli esempi di questo argomento viene illustrato l'uso dei metodi Skip e Take per eseguire una query su DataSet usando la sintassi delle espressioni di query.
Il metodo FillDataSet usato in questi esempi è specificato in Caricamento di dati in un DataSet.
Negli esempi di questo argomento vengono usate le tabelle Contact, Address, Product, SalesOrderHeader e SalesOrderDetail del database di esempio AdventureWorks.
Gli esempi in questo argomento usano le istruzioni using/Imports seguenti:
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
Per altre informazioni, vedere Procedura: Creare un progetto LINQ to DataSet in Visual Studio.
Ignora
Esempio
In questo esempio viene usato il metodo Skip per ottenere tutti gli indirizzi di Seattle ad eccezione dei primi due.
// 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
Take
Esempio
In questo esempio viene usato il metodo Take per ottenere i primi tre indirizzi di 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