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Exemplos de sintaxe de expressão de consulta: particionamento (LINQ to DataSet)

  • Artigo

Os exemplos neste tópico demonstram como usar os Skip métodos e Take para consultar um DataSet usando a sintaxe da expressão de consulta.

O FillDataSet método usado nesses exemplos é especificado em Carregando dados em um DataSet.

Os exemplos neste tópico usam as tabelas Contact, Address, Product, SalesOrderHeader e SalesOrderDetail no banco de dados de exemplo AdventureWorks.

Os exemplos neste tópico usam as seguintes using/Imports instruções:

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

Para obter mais informações, consulte Como criar um projeto LINQ to DataSet no Visual Studio.

Ignorar

Exemplo

Este exemplo usa o Skip método para obter todos, exceto os dois primeiros endereços em 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")
    }).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

Realizar

Exemplo

Este exemplo usa o Take método para obter os três primeiros endereços em 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

Consulte também