Exemplos de sintaxe da expressão de consulta: Operadores de elemento (LINQ to DataSet)Query Expression Syntax Examples: Element Operators (LINQ to DataSet)

Os exemplos neste tópico demonstram como usar os métodos de First e de ElementAt para obter os elementos de DataRow de DataSet usando a sintaxe da expressão de consulta.The examples in this topic demonstrate how to use the First and ElementAt methods to get DataRow elements from a DataSet using the query expression syntax.

O FillDataSet método usado nesses exemplos é especificado no carregamento de dados em um conjunto.The FillDataSet method used in these examples is specified in Loading Data Into a DataSet.

Os exemplos neste tópico usam as tabelas Contact, Address, Product, SalesOrderHeader e SalesOrderDetail no banco de dados de exemplo AdventureWorks.The examples in this topic use the Contact, Address, Product, SalesOrderHeader, and SalesOrderDetail tables in the AdventureWorks sample database.

Os exemplos neste tópico usam as seguintes using / Imports instruções:The examples in this topic use the following using/Imports statements:

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Data.Common;
using System.Globalization;
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 de LINQ to DataSet no Visual Studio.For more information, see How to: Create a LINQ to DataSet Project In Visual Studio.

ElementAtElementAt

ExemploExample

Este exemplo usa o método de ElementAt para recuperar o quinto endereço onde o == “M4B 1V7” de PostalCode .This example uses the ElementAt method to retrieve the fifth address where PostalCode == "M4B 1V7".

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

DataTable addresses = ds.Tables["Address"];

var fifthAddress = (
    from address in addresses.AsEnumerable()
    where address.Field<string>("PostalCode") == "M4B 1V7"
    select address.Field<string>("AddressLine1"))
.ElementAt(5);

Console.WriteLine("Fifth address where PostalCode = 'M4B 1V7': {0}",
    fifthAddress);
' 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 fifthAddress = ( _
    From address In addresses.AsEnumerable() _
    Where address.Field(Of String)("PostalCode") = "M4B 1V7" _
    Select address.Field(Of String)("AddressLine1")).ElementAt(5)

Console.WriteLine("Fifth address where PostalCode = 'M4B 1V7': " & _
        fifthAddress)

PrimeiroFirst

ExemploExample

Este exemplo usa o método de First para retornar o primeiro contato cujo nome é “Brooke”.This example uses the First method to return the first contact whose first name is 'Brooke'.

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

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

DataRow query = (
    from contact in contacts.AsEnumerable()
    where (string)contact["FirstName"] == "Brooke"
    select contact)
    .First();

Console.WriteLine("ContactID: " + query.Field<int>("ContactID"));
Console.WriteLine("FirstName: " + query.Field<string>("FirstName"));
Console.WriteLine("LastName: " + query.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 query = ( _
    From contact In contacts.AsEnumerable() _
    Where contact.Field(Of String)("FirstName") = "Brooke" _
    Select contact).First()

Console.WriteLine("ContactID: " & query.Field(Of Integer)("ContactID"))
Console.WriteLine("FirstName: " & query.Field(Of String)("FirstName"))
Console.WriteLine("LastName: " & query.Field(Of String)("LastName"))

Consulte tambémSee also