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Exemplos de sintaxe da consulta com base em método: Projeção (LINQ to DataSet)

Os exemplos neste tópico demonstram como usar os métodos Select e SelectMany para consultar um DataSet usando a sintaxe de consulta baseada em método.

O FillDataSet método usado nesses exemplos é especificado no carregamento de dados em um conjunto de dados.

Os exemplos deste tópico utilizam 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.

Selecionar

Exemplo

Este exemplo usa o Select método para projetar o Name, ProductNumbere ListPrice propriedades para uma sequência de tipos anônimos. A propriedade ListPrice também é renomeada para Price no tipo resultante.

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

DataTable products = ds.Tables["Product"];

var query = products.AsEnumerable().
    Select(product => new
    {
        ProductName = product.Field<string>("Name"),
        ProductNumber = product.Field<string>("ProductNumber"),
        Price = product.Field<decimal>("ListPrice")
    });

Console.WriteLine("Product Info:");
foreach (var productInfo in query)
{
    Console.WriteLine($"Product name: {productInfo.ProductName} Product number: {productInfo.ProductNumber} List price: ${productInfo.Price} ");
}

' 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 query = products.AsEnumerable() _
    .Select(Function(product As DataRow) New With _
    { _
        .ProductName = product.Field(Of String)("Name"), _
        .ProductNumber = product.Field(Of String)("ProductNumber"), _
        .Price = product.Field(Of Decimal)("ListPrice") _
    })

Console.WriteLine("Product Info:")
For Each product In query
    Console.Write("Product name: " & product.ProductName)
    Console.Write("Product number: " & product.ProductNumber)
    Console.WriteLine("List price: $ " & product.Price)
Next

SelectMany

Exemplo

Este exemplo usa o SelectMany método para selecionar todos os pedidos com TotalDue menos de 500,00.

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

var contacts = ds.Tables["Contact"].AsEnumerable();
var orders = ds.Tables["SalesOrderHeader"].AsEnumerable();

var query =
    contacts.SelectMany(
        contact => orders.Where(order =>
            (contact.Field<Int32>("ContactID") == order.Field<Int32>("ContactID"))
                && order.Field<decimal>("TotalDue") < 500.00M)
            .Select(order => new
            {
                ContactID = contact.Field<int>("ContactID"),
                LastName = contact.Field<string>("LastName"),
                FirstName = contact.Field<string>("FirstName"),
                OrderID = order.Field<int>("SalesOrderID"),
                Total = order.Field<decimal>("TotalDue")
            }));

foreach (var smallOrder in query)
{
    Console.WriteLine("Contact ID: {0} Name: {1}, {2} Order ID: {3} Total Due: ${4} ",
        smallOrder.ContactID, smallOrder.LastName, smallOrder.FirstName,
        smallOrder.OrderID, smallOrder.Total);
}

' 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 = ds.Tables("Contact").AsEnumerable()
Dim orders = ds.Tables("SalesOrderHeader").AsEnumerable()

Dim query = _
    contacts.SelectMany( _
        Function(contact) orders.Where(Function(order) _
            (contact.Field(Of Int32)("ContactID") = order.Field(Of Int32)("ContactID")) _
                And order.Field(Of Decimal)("TotalDue") < 500D) _
            .Select(Function(order) New With _
            { _
                .ContactID = contact.Field(Of Integer)("ContactID"), _
                .LastName = contact.Field(Of String)("LastName"), _
                .FirstName = contact.Field(Of String)("FirstName"), _
                .OrderID = order.Field(Of Integer)("SalesOrderID"), _
                .Total = order.Field(Of Decimal)("TotalDue") _
            }))

For Each smallOrder In query
    Console.Write("ContactID: " & smallOrder.ContactID)
    Console.Write(" Name: " & smallOrder.LastName & ", " & smallOrder.FirstName)
    Console.Write(" Order ID: " & smallOrder.OrderID)
    Console.WriteLine(" Total Due: $" & smallOrder.Total)
Next

Exemplo

Este exemplo usa o SelectMany método para selecionar todos os pedidos em que o pedido foi feito em 1º de outubro de 2002 ou posterior.

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

var contacts = ds.Tables["Contact"].AsEnumerable();
var orders = ds.Tables["SalesOrderHeader"].AsEnumerable();

var query =
    contacts.SelectMany(
        contact => orders.Where(order =>
            (contact.Field<Int32>("ContactID") == order.Field<Int32>("ContactID"))
                && order.Field<DateTime>("OrderDate") >= new DateTime(2002, 10, 1))
            .Select(order => new
            {
                ContactID = contact.Field<int>("ContactID"),
                LastName = contact.Field<string>("LastName"),
                FirstName = contact.Field<string>("FirstName"),
                OrderID = order.Field<int>("SalesOrderID"),
                OrderDate = order.Field<DateTime>("OrderDate")
            }));

foreach (var order in query)
{
    Console.WriteLine("Contact ID: {0} Name: {1}, {2} Order ID: {3} Order date: {4:d} ",
        order.ContactID, order.LastName, order.FirstName,
        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 contacts = ds.Tables("Contact").AsEnumerable()
Dim orders = ds.Tables("SalesOrderHeader").AsEnumerable()

Dim query = _
    contacts.SelectMany( _
        Function(contact) orders.Where(Function(order) _
            (contact.Field(Of Int32)("ContactID") = order.Field(Of Int32)("ContactID")) _
                And order.Field(Of DateTime)("OrderDate") >= New DateTime(2002, 10, 1)) _
            .Select(Function(order) New With _
                { _
                    .ContactID = contact.Field(Of Integer)("ContactID"), _
                    .LastName = contact.Field(Of String)("LastName"), _
                    .FirstName = contact.Field(Of String)("FirstName"), _
                    .OrderID = order.Field(Of Integer)("SalesOrderID"), _
                    .OrderDate = order.Field(Of DateTime)("OrderDate") _
                }))

For Each order In query
    Console.Write("Contact ID: " & order.ContactID)
    Console.Write(" Name: " & order.LastName & ", " & order.FirstName)
    Console.Write(" Order ID: " & order.OrderID)
    Console.WriteLine(" Order date: {0:d}", order.OrderDate)
Next

Consulte também

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