System.Data.Common 命名空間提供用於創建與特定數據源一起使用的 DbProviderFactory 實例的類。當創建 DbProviderFactory 實例並向其傳遞有關數據提供程序的信息時，DbProviderFactory 可以根據爲其提供的信息確定要返回的正確的強類型連接對象。
每個公開 DbProviderFactory 的 .NET Framework 數據提供程序都會在 machine.config 文件中註冊配置信息和一個提供程序字符串。.NET Framework 中具有已註冊的工廠類的數據提供程序包括 System.Data.Odbc、System.Data.OleDb、System.Data.SqlClient、System.Data.SqlServerCe 和 System.Data.OracleClient。
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Table 1. Provider-specific classes and generic interfaces in ADO.NET 1.0/1.1
| SqlClient class | Oracle class | Generic interface |
|---|---|---|
| SqlConnection | OracleConnection | IDbConnection |
| SqlCommand | OracleCommand | IDbCommand |
| SqlDataReader | OracleDataReader | IDataReader/IDataRecord |
| SqlTransaction | OracleTransaction | IDbTransaction |
| SqlParameter | OracleParameter | IDbDataParameter |
| SqlParameterCollection | OracleParameterCollection | IDataParameterCollection |
| SqlDataAdapter | OracleDataAdapter | IDbDataAdapter |
In ADO.NET 1.0 and 1.1, programmers had two choices. They could code to the provider-specific classes or the generic interfaces. If there was the possibility that the company database could change during the projected lifetime of the software, or if the product was a commercial package intended to support customers with different databases, they had to program with the generic interfaces. You can't call a constructor on an interface, so most generic programs included code that accomplished the task of obtaining the original IDbConnection by calling "new" on the appropriate provider-specific class, like this.
enum provider {sqlserver, oracle, oledb, odbc};
public IDbConnection GetConnectionInterface()
{
// determine provider from configuration
provider prov = GetProviderFromConfigFile();
IDbConnection conn = null;
switch (prov) {
case provider.sqlserver:
conn = new SqlConnection(); break;
case provider.oracle:
conn = new OracleConnection(); break;
// add new providers as the application supports them
}
return conn;
}
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Table 2. Generic base classes and Generic interfaces in ADO.NET 2.0
| SqlClient class | Base class | Generic interface |
|---|---|---|
| SqlConnection | DbConnection | IDbConnection |
| SqlCommand | DbCommand | IDbCommand |
| SqlDataReader | DbDataReader | IDataReader/IDataRecord |
| SqlTransaction | DbTransaction | IDbTransaction |
| SqlParameter | DbParameter | IDbDataParameter |
| SqlParameterCollection | DbParameterCollection | IDataParameterCollection |
| SqlDataAdapter | DbDataAdapter* | IDbDataAdapter |
| SqlCommandBuilder | DbCommandBuilder | |
| SqlConnectionStringBuilder | DbConnectionStringBuilder | |
| SqlPermission | DBDataPermission* |
In addition to these "main" base classes, many new base classes were added in ADO.NET 2.0, including some that we'll be talking about later in this article. The provider base classes in ADO.NET are abstract, however, meaning that they can't be instantiated directly. Our interface-based code above would change to:
enum provider {sqlserver, oracle, oledb, odbc};
public DbConnection GetConnectionBaseClass()
{
// determine provider from configuration
provider prov = GetProviderFromConfigFile();
DbConnection conn = null;
switch (prov) {
case provider.sqlserver:
conn = new SqlConnection(); break;
case provider.oracle:
conn = new OracleConnection(); break;
// add new providers as the application supports them
}
return conn;
}
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Provider FactoriesRather than rely on the case statements above, it would be nice to have a class that gave out a DbConnection based on instantiating "the correct" provider-specific connection. But how to know whether to instantiate SqlConnection or OracleConnection? The solution to this is to use a Provider Factory class to give out the right type of concrete class. Each provider implements a provider factory class, e.g., SqlClientFactory, OracleClientFactory, and OleDbFactory. These classes all derive from DbProviderFactory and contain static methods (shared in Visual Basic .NET) to distribute classes that can be created. Here's the list of DbProviderFactory methods:
Table 3. DbProviderFactory Methods
| CreateConnection |
| CreateCommand |
| CreateCommandBuilder |
| CreateConnection |
| CreateConnectionStringBuilder |
| CreateDataAdapter |
| CreateDataSourceEnumerator |
| CreateParameter |
| CreatePermission |
public DbConnection GetInitializedConnectionBaseClass()
{
DbConnection conn = null;
ConnectionStringSettings s =
ConfigurationSettings.ConnectionStrings["Publications"];
DbProviderFactory f = DbProviderFactories.GetFactory(
s.ProviderName);
if ((f.SupportedClasses & DbProviderSupportedClasses.DbConnection) > 0)
{
conn = f.CreateConnection();
conn.ConnectionString = s.ConnectionString;
}
return conn;
}
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Table 4. DbProviderFactories methods
| DbProviderFactories Method | Purpose |
|---|---|
| GetFactoryClasses() | Returns a DataTable of provider information from the information in machine.config |
| GetFactory(DataRow) | Returns the correct DbProviderFactory instance given a DataRow from the DataTable produced by GetFactoryClasses |
| GetFactory(string) | Returns the correct DbProviderFactory instance given a provider-invariant name string that identifies the provider |
Table 5. Connection string names and values in different data providers
| Meaning | Odbc | OleDb | SqlClient | OracleClient |
|---|---|---|---|---|
| Source to connect to | Server | Data Source | Server or Data Source | Server or Data Source |
| User | UID | User ID | UID or User ID | User ID |
| Password | PWD | Password | PWD or Password | Password |
| Is a Windows login used? | Trusted_Connection | Integrated Security | Trusted_Connection or Integrated Security | Integrated Security |
| Database to connect to | Database | Initial Catalog | Database or Initial Catalog | N/A |
| Connection Pooling | OLE DB Services | Pooling | Pooling |
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Table 6. Parameter usage styles in different ADO.NET data providers
| Provider | Named/Positional | Parameter Marker |
|---|---|---|
| SqlClient | Named | @parmname |
| OracleClient | Named | :parmname (or parmname) |
| OleDb | Positional | ? |
| Odbc | Positional | ? |
-----------------------------------------------------------------------------------------------------------------------------------static void CreateDataAdapter(string providerName, string connectionString)
{
try
{
// Create the DbProviderFactory and DbConnection.
DbProviderFactory factory =
DbProviderFactories.GetFactory(providerName);
DbConnection connection = factory.CreateConnection();
connection.ConnectionString = connectionString;
using (connection)
{
// Define the query.
string queryString =
"SELECT CustomerID, CompanyName FROM Customers";
// Create the select command.
DbCommand command = factory.CreateCommand();
command.CommandText = queryString;
command.Connection = connection;
// Create the DbDataAdapter.
DbDataAdapter adapter = factory.CreateDataAdapter();
adapter.SelectCommand = command;
// Create the DbCommandBuilder.
DbCommandBuilder builder = factory.CreateCommandBuilder();
builder.DataAdapter = adapter;
// Get the insert, update and delete commands.
adapter.InsertCommand = builder.GetInsertCommand();
adapter.UpdateCommand = builder.GetUpdateCommand();
adapter.DeleteCommand = builder.GetDeleteCommand();
// Display the CommandText for each command.
Console.WriteLine("InsertCommand: {0}",
adapter.InsertCommand.CommandText);
Console.WriteLine("UpdateCommand: {0}",
adapter.UpdateCommand.CommandText);
Console.WriteLine("DeleteCommand: {0}",
adapter.DeleteCommand.CommandText);
// Fill the DataTable.
DataTable table = new DataTable();
adapter.Fill(table);
// Insert a new row.
DataRow newRow = table.NewRow();
newRow["CustomerID"] = "XYZZZ";
newRow["CompanyName"] = "XYZ Company";
table.Rows.Add(newRow);
adapter.Update(table);
// Display rows after insert.
Console.WriteLine();
Console.WriteLine("----List All Rows-----");
foreach (DataRow row in table.Rows)
{
Console.WriteLine("{0} {1}", row[0], row[1]);
}
Console.WriteLine("----After Insert-----");
// Edit an existing row.
DataRow[] editRow = table.Select("CustomerID = 'XYZZZ'");
editRow[0]["CompanyName"] = "XYZ Corporation";
adapter.Update(table);
// Display rows after update.
Console.WriteLine();
foreach (DataRow row in table.Rows)
{
Console.WriteLine("{0} {1}", row[0], row[1]);
}
Console.WriteLine("----After Update-----");
// Delete a row.
DataRow[] deleteRow = table.Select("CustomerID = 'XYZZZ'");
foreach (DataRow row in deleteRow)
{
row.Delete();
}
adapter.Update(table);
// Display rows after delete.
Console.WriteLine();
foreach (DataRow row in table.Rows)
{
Console.WriteLine("{0} {1}", row[0], row[1]);
}
Console.WriteLine("----After Delete-----");
Console.WriteLine("Customer XYZZZ was deleted.");
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
