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

Artigo
04/07/2023

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

O método FillDataSet usado nesses exemplos é especificado em Carregar 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 deste tópico usam as seguintes instruções using/Imports:

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, veja Como criar um projeto LINQ to DataSet no Visual Studio.

Selecionar

Exemplo

Este exemplo usa o método Select para retornar todas as linhas da tabela de Product e exibir os nomes de produto.

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

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

IEnumerable<DataRow> query =
    from product in products.AsEnumerable()
    select product;

Console.WriteLine("Product Names:");
foreach (DataRow p in query)
{
    Console.WriteLine(p.Field<string>("Name"));
}

' 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 = From product In products.AsEnumerable() _
            Select product
Console.WriteLine("Product Names:")
For Each p In query
    Console.WriteLine(p.Field(Of String)("Name"))
Next

Exemplo

Este exemplo usa Select para retornar somente uma sequência de nomes do produto.

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

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

IEnumerable<string> query =
    from product in products.AsEnumerable()
    select product.Field<string>("Name");

Console.WriteLine("Product Names:");
foreach (string productName in query)
{
    Console.WriteLine(productName);
}

' 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 = From product In products.AsEnumerable() _
            Select product.Field(Of String)("Name")

Console.WriteLine("Product Names:")
For Each productName In query
    Console.WriteLine(productName)
Next

SelectMany

Exemplo

Este exemplo usa From …, … (o equivalente do método SelectMany) para selecionar todos os pedidos onde TotalDue é menor que 500,00.

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

DataTable contacts = ds.Tables["Contact"];
DataTable orders = ds.Tables["SalesOrderHeader"];

var query =
    from contact in contacts.AsEnumerable()
    from order in orders.AsEnumerable()
    where contact.Field<int>("ContactID") == order.Field<int>("ContactID")
        && order.Field<decimal>("TotalDue") < 500.00M
    select 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 As DataTable = ds.Tables("Contact")
Dim orders As DataTable = ds.Tables("SalesOrderHeader")

Dim query = _
    From contact In contacts.AsEnumerable() _
    From order In orders.AsEnumerable() _
    Where (contact.Field(Of Integer)("ContactID") = _
        order.Field(Of Integer)("ContactID")) _
        And (order.Field(Of Decimal)("TotalDue") < 500D) _
    Select 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"), _
        .TotalDue = order.Field(Of Decimal)("TotalDue") _
    }

For Each smallOrder In query
    Console.Write("ContactID: " & smallOrder.ContactID)
    Console.Write(" Name: {0}, {1}", smallOrder.LastName, _
                       smallOrder.FirstName)
    Console.Write(" OrderID: " & smallOrder.OrderID)
    Console.WriteLine(" TotalDue: $" & smallOrder.TotalDue)
Next

Exemplo

Este exemplo usa From …, … (o equivalente do método SelectMany) para selecionar todos os pedidos feitos em 1º de outubro de 2002 ou posterior.

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

DataTable contacts = ds.Tables["Contact"];
DataTable orders = ds.Tables["SalesOrderHeader"];

var query =
    from contact in contacts.AsEnumerable()
    from order in orders.AsEnumerable()
    where contact.Field<int>("ContactID") == order.Field<int>("ContactID") &&
        order.Field<DateTime>("OrderDate") >= new DateTime(2002, 10, 1)
    select 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 As DataTable = ds.Tables("Contact")
Dim orders As DataTable = ds.Tables("SalesOrderHeader")

Dim query = _
    From contact In contacts.AsEnumerable() _
    From order In orders.AsEnumerable() _
    Where contact.Field(Of Integer)("ContactID") = order.Field(Of Integer)("ContactID") And _
        order.Field(Of DateTime)("OrderDate") >= New DateTime(2002, 10, 1) _
    Select 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

Exemplo

Este exemplo usa From …, … (o equivalente do método SelectMany) para selecionar todos os pedidos onde o total do pedido é maior que 10000,00 e usa a atribuição From para evitar solicitar o total duas vezes.

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

DataTable contacts = ds.Tables["Contact"];
DataTable orders = ds.Tables["SalesOrderHeader"];

var query =
    from contact in contacts.AsEnumerable()
    from order in orders.AsEnumerable()
    let total = order.Field<decimal>("TotalDue")
    where contact.Field<int>("ContactID") == order.Field<int>("ContactID") &&
          total >= 10000.0M
    select new
    {
        ContactID = contact.Field<int>("ContactID"),
        LastName = contact.Field<string>("LastName"),
        OrderID = order.Field<int>("SalesOrderID"),
        total
    };
foreach (var order in query)
{
    Console.WriteLine("Contact ID: {0} Last name: {1} Order ID: {2} Total: {3}",
        order.ContactID, order.LastName, order.OrderID, order.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 As DataTable = ds.Tables("Contact")
Dim orders As DataTable = ds.Tables("SalesOrderHeader")

Dim query = _
    From contact In contacts.AsEnumerable() _
    From order In orders.AsEnumerable() _
    Let total = order.Field(Of Decimal)("TotalDue") _
    Where contact.Field(Of Integer)("ContactID") = order.Field(Of Integer)("ContactID") And _
        total >= 10000D _
    Select New With _
        { _
           .ContactID = contact.Field(Of Integer)("ContactID"), _
           .LastName = contact.Field(Of String)("LastName"), _
           .OrderID = order.Field(Of Integer)("SalesOrderID"), _
           .OrderDate = order.Field(Of DateTime)("OrderDate"), _
           total _
        }

For Each order In query
    Console.Write("Contact ID: " & order.ContactID)
    Console.Write(" Last Name: " & order.LastName)
    Console.Write(" Order ID: " & order.OrderID)
    Console.WriteLine(" Total: $" & order.total)
Next

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

Selecionar

Exemplo

Exemplo

SelectMany

Exemplo

Exemplo

Exemplo

Confira também

Recursos adicionais