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.
