作者：未知 来源：月光软件站 加入时间：2005-2-28　月光软件站

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.

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