[英]Are DbProviderFactory, DbConnection, DbCommand, and DbDataAdapter Thread-Safe?
[英]How to create a DbDataAdapter given a DbCommand or DbConnection?
我想創建一個適用於任何數據提供者的數據訪問層。
我知道可以使用連接上可用的工廠方法創建DbCommand
。
objDbCon.CreateCommand();
但是,我找不到任何東西來創建DbDataAdapter
。 這是ADO.NET中的一個錯誤還是什么?
從.NET 4.5開始 ,在編寫與提供程序無關的代碼時,您現在可以使用接受DbConnection
的DbProviderFactories.GetFactory
重載來獲取正確的提供程序工廠,然后可以從中創建數據適配器。
例:
DbDataAdapter CreateDataAdapter(DbConnection connection)
{
return DbProviderFactories.GetFactory(connection).CreateDataAdapter();
}
似乎有人在ADO.NET團隊中讀到了Ian Boyd評論他的回答...... :)
雖然謝爾蓋很好地回答了這個問題,但我花了一點時間才將其翻譯成我自己的需要。 所以我的理解是,如果你有一個DbConnection,但知道你在底層使用SqlClient,你的代碼看起來像:
DbDataAdapter da = DbProviderFactories.GetFactory("System.Data.SqlClient").CreateDataAdapter();
private static DbDataAdapter CreateDataAdapter(DbCommand cmd)
{
DbDataAdapter adapter;
/*
* DbProviderFactories.GetFactory(DbConnection connection) seams buggy
* (.NET Framework too old?)
* this is a workaround
*/
string name_space = cmd.Connection.GetType().Namespace;
DbProviderFactory factory = DbProviderFactories.GetFactory(name_space);
adapter = factory.CreateDataAdapter();
adapter.SelectCommand = cmd;
return adapter;
}
鑒於您不知道給定的連接類型,.NET沒有提供解決問題的好方法。 這是我們使用的:
/// <summary>
/// Construct a DataAdapater based on the type of DbConnection passed.
/// You can call connection.CreateCommand() to create a DbCommand object,
/// but there's no corresponding connection.CreateDataAdapter() method.
/// </summary>
/// <param name="connection"></param>
/// <exception>Throws Exception if the connection is not of a known type.</exception>
/// <returns></returns>
public static DbDataAdapter CreateDataAdapter(DbConnection connection)
{
//Note: Any code is released into the public domain. No attribution required.
DbDataAdapter adapter; //we can't construct an adapter directly
//So let's run around the block 3 times, before potentially crashing
if (connection is System.Data.SqlClient.SqlConnection)
adapter = new System.Data.SqlClient.SqlDataAdapter();
else if (connection is System.Data.OleDb.OleDbConnection)
adapter = new System.Data.OleDb.OleDbDataAdapter();
else if (connection is System.Data.Odbc.OdbcConnection)
adapter = new System.Data.Odbc.OdbcDataAdapter();
else if (connection is System.Data.SqlServerCe.SqlCeConnection)
adapter = new System.Data.SqlServerCe.SqlCeDataAdapter ();
else if (connection is Oracle.ManagedDataAccess.Client.OracleConnection)
adapter = new Oracle.ManagedDataAccess.Client.OracleDataAdapter();
else if (connection is Oracle.DataAccess.Client.OracleConnection)
adapter = new Oracle.DataAccess.Client.OracleDataAdapter();
else if (connection is IBM.Data.DB2.DB2Connection)
adapter = new IBM.Data.DB2.DB2DataAdapter();
//TODO: Add more DbConnection kinds as they become invented
else
{
throw new Exception("[CreateDataAdapter] Unknown DbConnection type: " + connection.GetType().FullName);
}
return adapter;
}
您可以使用其他方法在沒有DbDataAdapter的情況下將數據導入DataTable。
這是我的代碼
DataTable dt = new DataTable();
using (IDataReader dr = com.ExecuteReader())
{
if (dr.FieldCount > 0)
{
for (int i = 0; i < dr.FieldCount; i++)
{
DataColumn dc = new DataColumn(dr.GetName(i), dr.GetFieldType(i));
dt.Columns.Add(dc);
}
object[] rowobject = new object[dr.FieldCount];
while (dr.Read())
{
dr.GetValues(rowobject);
dt.LoadDataRow(rowobject, true);
}
}
}
return dt;
Necromancing。
如果您的.NET 4.5以下,那么您可以從受保護的屬性DbProviderFactory中獲取它與已編譯的Linq-Expression的連接:
namespace System.Data.Common
{
public static class ProviderExtensions
{
private static System.Func<System.Data.Common.DbConnection, System.Data.Common.DbProviderFactory> s_func;
static ProviderExtensions()
{
System.Linq.Expressions.ParameterExpression p = System.Linq.Expressions.Expression.Parameter(typeof(System.Data.Common.DbConnection));
System.Linq.Expressions.MemberExpression prop = System.Linq.Expressions.Expression.Property(p, "DbProviderFactory");
System.Linq.Expressions.UnaryExpression con = System.Linq.Expressions.Expression.Convert(prop, typeof(System.Data.Common.DbProviderFactory));
System.Linq.Expressions.LambdaExpression exp = System.Linq.Expressions.Expression.Lambda(con, p);
s_func = (Func<System.Data.Common.DbConnection, System.Data.Common.DbProviderFactory>)exp.Compile();
} // End Static Constructor
public static System.Data.Common.DbProviderFactory GetProviderByReflection(System.Data.Common.DbConnection conn)
{
System.Type t = conn.GetType();
System.Reflection.PropertyInfo pi = t.GetProperty("DbProviderFactory",
System.Reflection.BindingFlags.NonPublic
| System.Reflection.BindingFlags.Instance
);
return (System.Data.Common.DbProviderFactory)pi.GetValue(conn);
} // End Function GetProviderByReflection
public static System.Data.Common.DbProviderFactory GetProvider(this System.Data.Common.DbConnection connection)
{
return s_func(connection);
} // End Function GetProvider
public static System.Data.Common.DbDataAdapter CreateDataAdapter(this System.Data.Common.DbConnection connection)
{
System.Data.Common.DbProviderFactory fact = GetProvider(connection);
return fact.CreateDataAdapter();
} // End Function CreateDataAdapter
public static System.Data.Common.DbDataAdapter CreateDataAdapter(this System.Data.Common.DbConnection connection, System.Data.Common.DbCommand cmd)
{
System.Data.Common.DbProviderFactory fact = GetProvider(connection);
System.Data.Common.DbDataAdapter da = fact.CreateDataAdapter();
da.SelectCommand = cmd;
return da;
} // End Function CreateDataAdapter
}
}
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