Esempi di codice ADO.NET
Gli elenchi di codice inclusi in questa pagina illustrano come recuperare dati da un database usando le tecnologie ADO.NET seguenti:
Provider di dati 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)
Esempi di provider di dati ADO.NET
Gli elenchi di codice seguenti illustrano come recuperare i dati da un database usando i provider di dati ADO.NET. I dati vengono restituiti in un DataReader. Per altre informazioni, vedere Recupero di dati usando un DataReader.
SqlClient
Nel codice di questo esempio si presume che sia possibile effettuare la connessione al database di esempio Northwind in Microsoft SQL Server. Tramite il codice viene creato un oggetto SqlCommand per selezionare le righe dalla tabella Products e viene aggiunto un oggetto SqlParameter per limitare i risultati alle righe in cui UnitPrice è maggiore del valore del parametro specificato, in questo caso 5. L'oggetto SqlConnection viene aperto in un blocco using, garantendo che le risorse vengano chiuse ed eliminate al termine dell'esecuzione del codice. Il comando viene eseguito dal codice tramite un oggetto SqlDataReader e i risultati vengono visualizzati nella finestra della console. Se si usa System.Data.SqlClient, è consigliabile eseguire l'aggiornamento a Microsoft.Data.SqlClient perché sono in corso investimenti futuri e nuovi sviluppi di funzionalità. Per altre informazioni, vedere la presentazione del nuovo 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
Nel codice di questo esempio si presuppone che sia possibile effettuare la connessione al database di esempio Northwind di Microsoft Access. Tramite il codice viene creato un oggetto OleDbCommand per selezionare le righe dalla tabella Products e viene aggiunto un oggetto OleDbParameter per limitare i risultati alle righe in cui UnitPrice è maggiore del valore del parametro specificato, in questo caso 5. L'oggetto OleDbConnection viene aperto in un blocco using, garantendo che le risorse vengano chiuse ed eliminate al termine dell'esecuzione del codice. Il comando viene eseguito dal codice tramite un oggetto OleDbDataReader e i risultati vengono visualizzati nella finestra della 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
Nel codice di questo esempio si presuppone che sia possibile effettuare la connessione al database di esempio Northwind di Microsoft Access. Tramite il codice viene creato un oggetto OdbcCommand per selezionare le righe dalla tabella Products e viene aggiunto un oggetto OdbcParameter per limitare i risultati alle righe in cui UnitPrice è maggiore del valore del parametro specificato, in questo caso 5. L'oggetto OdbcConnection viene aperto in un blocco using, garantendo che le risorse vengano chiuse ed eliminate al termine dell'esecuzione del codice. Il comando viene eseguito dal codice tramite un oggetto OdbcDataReader e i risultati vengono visualizzati nella finestra della 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
Nel codice di questo esempio si presuppone che sia stata effettuata una connessione a DEMO.CUSTOMER in un server Oracle. È inoltre necessario aggiungere un riferimento a System.Data.OracleClient.dll. Il codice restituisce i dati in un oggetto 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
Esempi di Entity Framework
I listati di codice seguenti illustrano come recuperare i dati da un'origine dati eseguendo una query sulle entità in Entity Data Model (EDM). Questi esempi usano un modello basato sul database di esempio Northwind. Per altre informazioni su Entity Framework, vedere Panoramica di Entity Framework.
LINQ to Entities
Nel codice di questo esempio viene usata una query LINQ per restituire i dati come oggetti Categories, proiettati come tipo anonimo che contiene solo le proprietà CategoryID e CategoryName. Per altre informazioni, vedere Panoramica di 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
Oggetto ObjectQuery tipizzato
Nel codice di questo esempio viene usato un oggetto ObjectQuery<T> per restituire i dati come oggetti Categories. Per altre informazioni, vedere Query di oggetto.
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
Nel codice di questo esempio viene usato un oggetto EntityCommand per eseguire una query Entity SQL. Questa query restituisce un elenco di record che rappresentano istanze del tipo di entità Categories. Per accedere ai record di dati nel set di risultati viene usato un oggetto EntityDataReader. Per ulteriori informazioni, vedere Provider EntityClient per 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
Nel codice di questo esempio viene usata una query LINQ per restituire i dati come oggetti Categories, proiettati come tipo anonimo che contiene solo le proprietà CategoryID e CategoryName. Questo esempio è basato sul contesto dati di Northwind. Per altre informazioni, vedere Introduzione a .NET Framework.
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