简介
本系列的最后一篇文章.第一部分如何描述,二部分如何取得描述.现在我们就要创建DAL库来使我们的标题可行.

设计DAL库
我想创建的类库支持Sqlserver 和oledb.我把库分成了以下的部分:

Utility classes
class DALQueryBuilder
生成sql语句更新物件.

class DALParameter
生成参数保存在存储过程中.

class DALException
继承于System.Exception , 数据库有异常时将会提供更多的信息.

Attribute classes
参见第一篇.

DAL 本身
class DALEngine
这个抽象的类用于数据库操作,是数据库程序更加简单.它的虚拟和抽象的方法有不同的实施.

class DALSqlEngine


class DALOleDbEngine
耧一眼DALEngine 类
public abstract class DALEngine : IDisposable
{
//
// private data members
//
IDbConnection conn = null;
string connectionString = "";
ArrayList parameters = new ArrayList();
bool canClose = true;


// constructor
public DALEngine(string connectionString);

public bool CanClose;
public string ConnectionString;


protected IDbConnection Connection;
protected ArrayList Parameters;

public void Close();
public void Dispose();


//
// methods that must be override with a specific data provider
// implementation please see the implementation of DALSqlEngine
// or DALOleDbEngine
//
protected abstract IDbConnection GetConnection();
protected abstract IDbCommand CreateCommand(string spName);
public abstract void ExecSP_DataSet(string spName, DataSet dataSet,
string tableName);
public abstract void ExecQuery_DataSet(string query, DataSet dataSet,
string tableName);


//
// related to stored procedure parameters
//
public DALParameter GetParameter(string name);
void UpdateOutputParameters(IDbCommand cmd);
public void AddParameter(DALParameter param);
public void ClearParameters();


//
// for those that use stored procedures
//
public IDataReader ExecSP_DataReader(string spName);
public IDataReader ExecSP_DataReader(string spName,
CommandBehavior behavior);
public object ExecSP_Scalar(string spName);
public int ExecSP_NonQuery(string spName);


//
// methods for those that use plain SQL statements
//
public IDataReader ExecQuery_DataReader(string query,
CommandBehavior behavior);
public IDataReader ExecQuery_DataReader(string query);
public object ExecQuery_Scalar(string query);
public int ExecQuery_NonQuery(string query);




//
// Business objects methods
//
public static object CreateFromReader(IDataReader reader, Type objType);
public object RetrieveObject(object keyValue, Type objType);
public int RetrieveChildObjects(object foreignKeyValue, ArrayList objects,
Type childType);
void UpdateObjectSql(object o, DataTableAttribute dataTable);
void UpdateObjectStoredProcedure(object o, DataTableAttribute dataTable);
public void UpdateObject(object o);
public void UpdateObjects(IEnumerable enumObjects);
}

public class DAL : DALSqlEngine
{
const string CONN_STRING = "server=localhost;uid=sa;pwd=;database=pubs";

public DAL() : base(CONN_STRING)
{

}

public ArrayList GetCustomerDependents(Customer customer)
{