Exemplos de código do ADO.NET
As listagens de código deste tópico demonstram como recuperar dados de um banco de dados usando as seguintes tecnologias do ADO.NET:
Provedores de dados do ADO.NET:
SqlClient (
System.Data.SqlClient)OleDb (
System.Data.OleDb)Odbc (
System.Data.Odbc)OracleClient (
System.Data.OracleClient)
ADO.NET Entity Framework:
EntityClient (
System.Data.EntityClient)
Exemplos de provedor de dados do ADO.NET
As listagens de código a seguir demonstram como recuperar dados de um banco de dados usando provedores de dados do ADO.NET. Os dados são retornados em um DataReader. Para obter mais informações, confira Como recuperar dados usando um DataReader.
SqlClient
O código desse exemplo pressupõe que você possa se conectar ao banco de dados de exemplo Northwind no Microsoft SQL Server. O código cria um SqlCommand para selecionar linhas da tabela Products, adicionando um SqlParameter para restringir os resultados às linhas com um UnitPrice maior que o valor do parâmetro especificado, neste caso, 5. A SqlConnection é aberta em um bloco using, o que garante que os recursos sejam fechados e descartados quando o código for fechado. O código executa o comando usando um SqlDataReader e exibe os resultados na janela do console. Se você estiver usando System.Data.SqlClient, considere a atualização para Microsoft.Data.SqlClient, pois ele é a versão em que os investimentos futuros e os novos desenvolvimentos de recursos estão sendo feitos. Para obter mais informações, confira Introdução ao novo Microsoft.Data.SqlClient.
using System;
using System.Data.SqlClient;
static class Program
{
static void Main()
{
const string connectionString =
"Data Source=(local);Initial Catalog=Northwind;"
+ "Integrated Security=true";
// Provide the query string with a parameter placeholder.
const string queryString =
"SELECT ProductID, UnitPrice, ProductName from dbo.products "
+ "WHERE UnitPrice > @pricePoint "
+ "ORDER BY UnitPrice DESC;";
// Specify the parameter value.
const int paramValue = 5;
// Create and open the connection in a using block. This
// ensures that all resources will be closed and disposed
// when the code exits.
using (SqlConnection connection =
new(connectionString))
{
// Create the Command and Parameter objects.
SqlCommand command = new(queryString, connection);
command.Parameters.AddWithValue("@pricePoint", paramValue);
// Open the connection in a try/catch block.
// Create and execute the DataReader, writing the result
// set to the console window.
try
{
connection.Open();
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Console.WriteLine("\t{0}\t{1}\t{2}",
reader[0], reader[1], reader[2]);
}
reader.Close();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.ReadLine();
}
}
Option Explicit On
Option Strict On
Imports System.Data
Imports System.Data.SqlClient
Public Class Program
Public Shared Sub Main()
Dim connectionString As String = _
"Data Source=(local);Initial Catalog=Northwind;" _
& "Integrated Security=true"
' Provide the query string with a parameter placeholder.
Dim queryString As String = _
"SELECT ProductID, UnitPrice, ProductName from dbo.Products " _
& "WHERE UnitPrice > @pricePoint " _
& "ORDER BY UnitPrice DESC;"
' Specify the parameter value.
Dim paramValue As Integer = 5
' Create and open the connection in a using block. This
' ensures that all resources will be closed and disposed
' when the code exits.
Using connection As New SqlConnection(connectionString)
' Create the Command and Parameter objects.
Dim command As New SqlCommand(queryString, connection)
command.Parameters.AddWithValue("@pricePoint", paramValue)
' Open the connection in a try/catch block.
' Create and execute the DataReader, writing the result
' set to the console window.
Try
connection.Open()
Dim dataReader As SqlDataReader = _
command.ExecuteReader()
Do While dataReader.Read()
Console.WriteLine( _
vbTab & "{0}" & vbTab & "{1}" & vbTab & "{2}", _
dataReader(0), dataReader(1), dataReader(2))
Loop
dataReader.Close()
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
Console.ReadLine()
End Using
End Sub
End Class
OleDb
O código neste exemplo pressupõe que você pode se conectar ao banco de dados Northwind do Microsoft Access. O código cria um OleDbCommand para selecionar linhas da tabela Products, adicionando um OleDbParameter para restringir os resultados às linhas com um UnitPrice maior que o valor do parâmetro especificado, neste caso, 5. O OleDbConnection é aberto dentro de um bloco using, o que garante que os recursos sejam fechados e descartados quando o código for fechado. O código executa o comando usando um OleDbDataReader e exibe os resultados na janela do console.
using System;
using System.Data.OleDb;
using System.Runtime.Versioning;
// API is only supported on Windows
[SupportedOSPlatform("windows")]
static class Program
{
static void Main()
{
// The connection string assumes that the Access
// Northwind.mdb is located in the c:\Data folder.
const string connectionString =
"Provider=Microsoft.Jet.OLEDB.4.0;Data Source="
+ "c:\\Data\\Northwind.mdb;User Id=admin;Password=;";
// Provide the query string with a parameter placeholder.
const string queryString =
"SELECT ProductID, UnitPrice, ProductName from products "
+ "WHERE UnitPrice > ? "
+ "ORDER BY UnitPrice DESC;";
// Specify the parameter value.
const int paramValue = 5;
// Create and open the connection in a using block. This
// ensures that all resources will be closed and disposed
// when the code exits.
using (OleDbConnection connection =
new(connectionString))
{
// Create the Command and Parameter objects.
OleDbCommand command = new(queryString, connection);
command.Parameters.AddWithValue("@pricePoint", paramValue);
// Open the connection in a try/catch block.
// Create and execute the DataReader, writing the result
// set to the console window.
try
{
connection.Open();
OleDbDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Console.WriteLine("\t{0}\t{1}\t{2}",
reader[0], reader[1], reader[2]);
}
reader.Close();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.ReadLine();
}
}
Option Explicit On
Option Strict On
Imports System.Data
Imports System.Data.OleDb
Public Class Program
Public Shared Sub Main()
' The connection string assumes that the Access
' Northwind.mdb is located in the c:\Data folder.
Dim connectionString As String = _
"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" _
& "c:\Data\Northwind.mdb;User Id=admin;Password=;"
' Provide the query string with a parameter placeholder.
Dim queryString As String = _
"SELECT ProductID, UnitPrice, ProductName from Products " _
& "WHERE UnitPrice > ? " _
& "ORDER BY UnitPrice DESC;"
' Specify the parameter value.
Dim paramValue As Integer = 5
' Create and open the connection in a using block. This
' ensures that all resources will be closed and disposed
' when the code exits.
Using connection As New OleDbConnection(connectionString)
' Create the Command and Parameter objects.
Dim command As New OleDbCommand(queryString, connection)
command.Parameters.AddWithValue("@pricePoint", paramValue)
' Open the connection in a try/catch block.
' Create and execute the DataReader, writing the result
' set to the console window.
Try
connection.Open()
Dim dataReader As OleDbDataReader = _
command.ExecuteReader()
Do While dataReader.Read()
Console.WriteLine( _
vbTab & "{0}" & vbTab & "{1}" & vbTab & "{2}", _
dataReader(0), dataReader(1), dataReader(2))
Loop
dataReader.Close()
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
Console.ReadLine()
End Using
End Sub
End Class
Odbc
O código neste exemplo pressupõe que você pode se conectar ao banco de dados Northwind do Microsoft Access. O código cria um OdbcCommand para selecionar linhas da tabela Products, adicionando um OdbcParameter para restringir os resultados às linhas com um UnitPrice maior que o valor do parâmetro especificado, neste caso, 5. A OdbcConnection é aberta em um bloco using, o que garante que os recursos sejam fechados e descartados quando o código for fechado. O código executa o comando usando um OdbcDataReader e exibe os resultados na janela do console.
using System;
using System.Data.Odbc;
static class Program
{
static void Main()
{
// The connection string assumes that the Access
// Northwind.mdb is located in the c:\Data folder.
const string connectionString =
"Driver={Microsoft Access Driver (*.mdb)};"
+ "Dbq=c:\\Data\\Northwind.mdb;Uid=Admin;Pwd=;";
// Provide the query string with a parameter placeholder.
const string queryString =
"SELECT ProductID, UnitPrice, ProductName from products "
+ "WHERE UnitPrice > ? "
+ "ORDER BY UnitPrice DESC;";
// Specify the parameter value.
const int paramValue = 5;
// Create and open the connection in a using block. This
// ensures that all resources will be closed and disposed
// when the code exits.
using (OdbcConnection connection =
new(connectionString))
{
// Create the Command and Parameter objects.
OdbcCommand command = new(queryString, connection);
command.Parameters.AddWithValue("@pricePoint", paramValue);
// Open the connection in a try/catch block.
// Create and execute the DataReader, writing the result
// set to the console window.
try
{
connection.Open();
OdbcDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Console.WriteLine("\t{0}\t{1}\t{2}",
reader[0], reader[1], reader[2]);
}
reader.Close();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.ReadLine();
}
}
}
Option Explicit On
Option Strict On
Imports System.Data
Imports System.Data.Odbc
Public Class Program
Public Shared Sub Main()
' The connection string assumes that the Access
' Northwind.mdb is located in the c:\Data folder.
Dim connectionString As String = _
"Driver={Microsoft Access Driver (*.mdb)};" _
& "Dbq=c:\Data\Northwind.mdb;Uid=Admin;Pwd=;"
' Provide the query string with a parameter placeholder.
Dim queryString As String = _
"SELECT ProductID, UnitPrice, ProductName from Products " _
& "WHERE UnitPrice > ? " _
& "ORDER BY UnitPrice DESC;"
' Specify the parameter value.
Dim paramValue As Integer = 5
' Create and open the connection in a using block. This
' ensures that all resources will be closed and disposed
' when the code exits.
Using connection As New OdbcConnection(connectionString)
' Create the Command and Parameter objects.
Dim command As New OdbcCommand(queryString, connection)
command.Parameters.AddWithValue("@pricePoint", paramValue)
' Open the connection in a try/catch block.
' Create and execute the DataReader, writing the result
' set to the console window.
Try
connection.Open()
Dim dataReader As OdbcDataReader = _
command.ExecuteReader()
Do While dataReader.Read()
Console.WriteLine( _
vbTab & "{0}" & vbTab & "{1}" & vbTab & "{2}", _
dataReader(0), dataReader(1), dataReader(2))
Loop
dataReader.Close()
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
Console.ReadLine()
End Using
End Sub
End Class
OracleClient
O código neste exemplo pressupõe uma conexão a DEMO.CUSTOMER em um servidor Oracle. Você também deve adicionar uma referência ao System.Data.OracleClient.dll. O código retorna os dados em um OracleDataReader.
using System;
using System.Data.OracleClient;
static class Program
{
static void Main()
{
const string connectionString =
"Data Source=ThisOracleServer;Integrated Security=yes;";
const string queryString =
"SELECT CUSTOMER_ID, NAME FROM DEMO.CUSTOMER";
using (OracleConnection connection =
new(connectionString))
{
OracleCommand command = connection.CreateCommand();
command.CommandText = queryString;
try
{
connection.Open();
OracleDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Console.WriteLine("\t{0}\t{1}",
reader[0], reader[1]);
}
reader.Close();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
}
Option Explicit On
Option Strict On
Imports System.Data
Imports System.Data.OracleClient
Public Class Program
Public Shared Sub Main()
Dim connectionString As String = _
"Data Source=ThisOracleServer;Integrated Security=yes;"
Dim queryString As String = _
"SELECT CUSTOMER_ID, NAME FROM DEMO.CUSTOMER"
Using connection As New OracleConnection(connectionString)
Dim command As OracleCommand = connection.CreateCommand()
command.CommandText = queryString
Try
connection.Open()
Dim dataReader As OracleDataReader = _
command.ExecuteReader()
Do While dataReader.Read()
Console.WriteLine(vbTab & "{0}" & vbTab & "{1}", _
dataReader(0), dataReader(1))
Loop
dataReader.Close()
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
End Using
End Sub
End Class
Exemplos do Entity Framework
As seguintes listagens de código demonstram como recuperar dados de uma fonte de dados consultando entidades em um EDM (Modelo de Dados de Entidade). Esses exemplos usam um modelo baseado no banco de dados de exemplo Northwind. Para obter mais informações sobre o Entity Framework, confira Visão geral do Entity Framework.
LINQ to Entities
O código neste exemplo usa uma consulta LINQ para retornar dados como objetos Categories, que são projetados como um tipo anônimo que contém somente as propriedades CategoryID e CategoryName. Para obter mais informações, confira Visão geral do LINQ to Entities.
using System;
using System.Linq;
using System.Data.Objects;
using NorthwindModel;
class LinqSample
{
public static void ExecuteQuery()
{
using (NorthwindEntities context = new NorthwindEntities())
{
try
{
var query = from category in context.Categories
select new
{
categoryID = category.CategoryID,
categoryName = category.CategoryName
};
foreach (var categoryInfo in query)
{
Console.WriteLine("\t{0}\t{1}",
categoryInfo.categoryID, categoryInfo.categoryName);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
}
Option Explicit On
Option Strict On
Imports System.Linq
Imports System.Data.Objects
Imports NorthwindModel
Class LinqSample
Public Shared Sub ExecuteQuery()
Using context As NorthwindEntities = New NorthwindEntities()
Try
Dim query = From category In context.Categories _
Select New With _
{ _
.categoryID = category.CategoryID, _
.categoryName = category.CategoryName _
}
For Each categoryInfo In query
Console.WriteLine(vbTab & "{0}" & vbTab & "{1}", _
categoryInfo.categoryID, categoryInfo.categoryName)
Next
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
End Using
End Sub
End Class
ObjectQuery tipado
O código neste exemplo usa um ObjectQuery<T> para retornar dados como objetos Categories. Para obter mais informações, confira Consultas de objeto.
using System;
using System.Data.Objects;
using NorthwindModel;
class ObjectQuerySample
{
public static void ExecuteQuery()
{
using (NorthwindEntities context = new NorthwindEntities())
{
ObjectQuery<Categories> categoryQuery = context.Categories;
foreach (Categories category in
categoryQuery.Execute(MergeOption.AppendOnly))
{
Console.WriteLine("\t{0}\t{1}",
category.CategoryID, category.CategoryName);
}
}
}
}
Option Explicit On
Option Strict On
Imports System.Data.Objects
Imports NorthwindModel
Class ObjectQuerySample
Public Shared Sub ExecuteQuery()
Using context As NorthwindEntities = New NorthwindEntities()
Dim categoryQuery As ObjectQuery(Of Categories) = context.Categories
For Each category As Categories In _
categoryQuery.Execute(MergeOption.AppendOnly)
Console.WriteLine(vbTab & "{0}" & vbTab & "{1}", _
category.CategoryID, category.CategoryName)
Next
End Using
End Sub
End Class
EntityClient
O código neste exemplo usa um EntityCommand para executar uma consulta Entity SQL. Esta consulta retorna uma lista de registros que representam instâncias do tipo de entidade Categories. Um EntityDataReader é usado para acessar os registros de dados no conjunto de resultados. Para obter mais informações, consulte EntityClient Provider para o Entity Framework.
using System;
using System.Data;
using System.Data.Common;
using System.Data.EntityClient;
using NorthwindModel;
class EntityClientSample
{
public static void ExecuteQuery()
{
string queryString =
@"SELECT c.CategoryID, c.CategoryName
FROM NorthwindEntities.Categories AS c";
using (EntityConnection conn =
new EntityConnection("name=NorthwindEntities"))
{
try
{
conn.Open();
using (EntityCommand query = new EntityCommand(queryString, conn))
{
using (DbDataReader rdr =
query.ExecuteReader(CommandBehavior.SequentialAccess))
{
while (rdr.Read())
{
Console.WriteLine("\t{0}\t{1}", rdr[0], rdr[1]);
}
}
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
}
Option Explicit On
Option Strict On
Imports System.Data
Imports System.Data.Common
Imports System.Data.EntityClient
Imports NorthwindModel
Class EntityClientSample
Public Shared Sub ExecuteQuery()
Dim queryString As String = _
"SELECT c.CategoryID, c.CategoryName " & _
"FROM NorthwindEntities.Categories AS c"
Using conn As EntityConnection = _
New EntityConnection("name=NorthwindEntities")
Try
conn.Open()
Using query As EntityCommand = _
New EntityCommand(queryString, conn)
Using rdr As DbDataReader = _
query.ExecuteReader(CommandBehavior.SequentialAccess)
While rdr.Read()
Console.WriteLine(vbTab & "{0}" & vbTab & "{1}", _
rdr(0), rdr(1))
End While
End Using
End Using
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
End Using
End Sub
End Class
LINQ to SQL
O código neste exemplo usa uma consulta LINQ para retornar dados como objetos Categories, que são projetados como um tipo anônimo que contém somente as propriedades CategoryID e CategoryName. Este exemplo é baseado no contexto de dados do Northwind. Para saber mais, confira a Introdução.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Northwind;
class LinqSqlSample
{
public static void ExecuteQuery()
{
using (NorthwindDataContext db = new NorthwindDataContext())
{
try
{
var query = from category in db.Categories
select new
{
categoryID = category.CategoryID,
categoryName = category.CategoryName
};
foreach (var categoryInfo in query)
{
Console.WriteLine("vbTab {0} vbTab {1}",
categoryInfo.categoryID, categoryInfo.categoryName);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
}
Option Explicit On
Option Strict On
Imports System.Collections.Generic
Imports System.Linq
Imports System.Text
Imports Northwind
Class LinqSqlSample
Public Shared Sub ExecuteQuery()
Using db As NorthwindDataContext = New NorthwindDataContext()
Try
Dim query = From category In db.Categories _
Select New With _
{ _
.categoryID = category.CategoryID, _
.categoryName = category.CategoryName _
}
For Each categoryInfo In query
Console.WriteLine(vbTab & "{0}" & vbTab & "{1}", _
categoryInfo.categoryID, categoryInfo.categoryName)
Next
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
End Using
End Sub
End Class