Ejemplos de código de ADO.NET
En los listados de código de este tema, se muestra cómo recuperar datos de una base de datos mediante las tecnologías de ADO.NET siguientes:
Proveedores de datos 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)
Ejemplos del proveedor de datos ADO.NET
En los listados de código siguientes se muestra cómo recuperar datos de una base de datos usando proveedores de datos ADO.NET. Los datos se devuelven en DataReader. Para más información, consulte Recuperación de datos con un objeto DataReader.
SqlClient
En el código de este ejemplo, se presupone que puede conectarse a la base de datos de ejemplo Northwind en Microsoft SQL Server. El código crea SqlCommand para seleccionar filas de la tabla Products, que añade SqlParameter para limitar los resultados a las filas con un UnitPrice mayor que el valor de parámetro especificado, en este caso 5. SqlConnection se abre dentro de un bloque using, que garantiza que los recursos se cierran y se eliminan cuando termina la ejecución del código. El código ejecuta el comando utilizando SqlDataReader y muestra los resultados en la ventana de la consola. Si usa System.Data.SqlClient, debe considerar la posibilidad de actualizar a Microsoft.Data.SqlClient, ya que es donde se realizan inversiones futuras y desarrollos nuevos de características. Para obtener más información, vea Introducción al nuevo 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
En el código de este ejemplo se asume que puede conectarse a la base de datos de ejemplo Northwind de Microsoft Access. El código crea OleDbCommand para seleccionar filas de la tabla Products, que añade OleDbParameter para limitar los resultados a las filas con un UnitPrice mayor que el valor de parámetro especificado, en este caso 5. OleDbConnection se abre dentro de un bloque using, que garantiza que los recursos se cierran y se eliminan cuando termina la ejecución del código. El código ejecuta el comando utilizando OleDbDataReader y muestra los resultados en la ventana de la consola.
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
En el código de este ejemplo se asume que puede conectarse a la base de datos de ejemplo Northwind de Microsoft Access. El código crea OdbcCommand para seleccionar filas de la tabla Products, que añade OdbcParameter para limitar los resultados a las filas con un UnitPrice mayor que el valor de parámetro especificado, en este caso 5. OdbcConnection se abre dentro de un bloque using, que garantiza que los recursos se cierran y se eliminan cuando termina la ejecución del código. El código ejecuta el comando utilizando OdbcDataReader y muestra los resultados en la ventana de la consola.
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
En el código de este ejemplo se presupone una conexión a DEMO.CUSTOMER en un servidor Oracle. También debe agregarse una referencia a System.Data.OracleClient.dll. El código devuelve los datos en 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
Ejemplos de Entity Framework
En los listados de código siguientes se muestra cómo recuperar los datos de un origen de datos consultando las entidades de un Entity Data Model (EDM). En estos ejemplos, se usa un modelo basado en la base de datos de ejemplo Northwind. Para más información sobre Entity Framework, consulte Información general sobre Entity Framework.
LINQ to Entities
El código de este ejemplo usa una consulta LINQ para devolver los datos como objetos Categories, que se proyectan como un tipo anónimo que contiene solo las propiedades CategoryID y CategoryName. Para más información, consulte Información general sobre 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 con establecimiento de tipos
En el código de este ejemplo se utiliza ObjectQuery<T> para devolver los datos como objetos Categories. Para más información, consulte 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
El código de este ejemplo usa EntityCommand para ejecutar una consulta Entity SQL. Esta consulta devuelve una lista de registros que representan instancias del tipo de entidad Categories. Se usa EntityDataReader para obtener acceso a los registros de datos del conjunto de resultados. Para obtener más información, consulte Proveedor de EntityClient para 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 a SQL
El código de este ejemplo usa una consulta LINQ para devolver los datos como objetos Categories, que se proyectan como un tipo anónimo que contiene solo las propiedades CategoryID y CategoryName. Este ejemplo se basa en el contexto de datos Northwind. Para más información, consulte Introducción.
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