数据简介
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)
{
ArrayList result = new ArrayList();

RetrieveChildObjects(customer.Id, result, typeof(CustomerDependent));

return result;
}

public void UpdateCustomerDependents(Customer customer)
{
UpdateObjects(customer.Dependents);
}
}
看个例子:

public static void Main()
{

DAL dal = new DAL();

try
{

Contact contact = new Contact();
contact.Name = "Joao Cardoso";
contact.Age = 23;
contact.Address = "Av. Rio Branco, 202/121";
contact.Address2 = "Centro";
contact.PostalCode = "09029-901";
contact.City = "Sao Paulo";
contact.State = "SP";
contact.Country = "Brazil";

dal.UpdateObject(contact);
Console.WriteLine(contact);


Contact joaoCardoso = (Contact)dal.RetrieveObject(1, typeof(Contact));
joaoCardoso.Age++;
Console.WriteLine(joaoCardoso);
Console.WriteLine("");


Customer customer = new Customer();
customer.Name = "Paul Noyter";
customer.Age = 34;
customer.Address = "All St, 2202/2121";
customer.Address2 = "Downville";
customer.PostalCode = "90931";
customer.City = "Los Angeles";
customer.State = "CA";
customer.Country = "United States";
customer.TotalPurchased += 1900.87M;
customer.NumberOfPurchases++;

dal.UpdateObject(customer);


Customer paul = (Customer)dal.RetrieveObject(1, typeof(Customer));
Console.WriteLine(paul);

paul.TotalPurchased += 100M;
paul.NumberOfPurchases++;
dal.UpdateObject(paul);

if (paul.Dependents.Count == 0)
{
CustomerDependent dependent = paul.NewDependent();
dependent.Name = "Marie Noyter";
dependent.Age = 31;
paul.Dependents.Add(dependent);


dependent = paul.NewDependent();
dependent.Name = "Mark Noyter";
dependent.Age = 10;
paul.Dependents.Add(dependent);


dependent = paul.NewDependent();
dependent.Name = "Claudia Snorg";
dependent.Age = 32;
dependent.Relationship = CustomerRelationship.Friend;
paul.Dependents.Add(dependent);

dal.UpdateCustomerDependents(paul);
}
else
{
Console.WriteLine("Dependents of {0}", paul.Name);

foreach(CustomerDependent dependent in paul.Dependents)
{
Console.WriteLine("<Dependent>{0} - {1} [{2}]", dependent.Id,
dependent.Name, dependent.Relationship);
dependent.Relationship = CustomerRelationship.Family;
}

dal.UpdateCustomerDependents(paul);
}

}
finally
{
dal.Dispose();
}
}
Conclusion
有老多局限性,需要我们去进一步实施思考,但是你理解了这些以后,我们就可以进行nhibernate的理解研究和应用了,祝你好运.