ASP.NET：自定义实体类简介(6)

对于在许多数据绑定控件提供的 OnItemDataBound 或 OnItemCreated 中执行处理的人来说，您可能会将 e.Item.DataItem 强制转换成 DataRowView。当绑定到自定义集合时，e.Item.DataItem 则被强制转换成自定义实体，在我们的示例中为 User 类：

'Visual Basic .NET

Protected Sub r_ItemDataBound (s As Object, e As RepeaterItemEventArgs)

Dim type As ListItemType = e.Item.ItemType

If type = ListItemType.AlternatingItem OrElse

? type = ListItemType.Item Then

Dim u As Label = CType(e.Item.FindControl("userName"), Label)

Dim currentUser As User = CType(e.Item.DataItem, User)

If Not PasswordUtility.PasswordIsSecure(currentUser.Password) Then

ul.ForeColor = Drawing.Color.Red

End If

End If

End Sub

//C#

protected void r_ItemDataBound(object sender, RepeaterItemEventArgs e) {

ListItemType type = e.Item.ItemType;

if (type == ListItemType.AlternatingItem ||

? type == ListItemType.Item){

Label ul = (Label)e.Item.FindControl("userName");

User currentUser = (User)e.Item.DataItem;

if (!PasswordUtility.PasswordIsSecure(currentUser.Password)){

ul.ForeColor = Color.Red;

}

}

}

管理关系

即使在最简单的系统中，实体之间也存在关系。对于关系数据库，可以通过外键维护关系；而使用对象时，关系只是对另一个对象的引用。例如，根据我们前面的示例，User 对象完全可以具有一个 Role：

'Visual Basic .NET

Public Class User

Private _role As Role

Public Property Role() As Role

Get

Return _role

End Get

Set(ByVal Value As Role)

_role = Value

End Set

End Property

End Class

//C#

public class User {

private Role role;

public Role Role {

get {return role;}

set {role = value;}

}

}

或者一个 Role 集合：

'Visual Basic .NET

Public Class User

Private _roles As RoleCollection

Public ReadOnly Property Roles() As RoleCollection

Get

If _roles Is Nothing Then

_roles = New RoleCollection

End If

Return _roles

End Get

End Property

End Class

//C#

public class User {

private RoleCollection roles;

public RoleCollection Roles {

get {

if (roles == null){

roles = new RoleCollection();

}

return roles;

}

}

}

在这两个示例中，我们有一个虚构的 Role 类或 RoleCollection 类，它们就是类似于 User 和 UserCollection 类的其他自定义实体或集合类。

映射关系

真正的问题在于如何映射关系。让我们看一个简单的示例，我们希望根据 userId 及其角色来检索一个用户。首先，我们看一看关系模型：



图 3：User 与 Role 之间的关系

这里，我们看到了一个 User 表和一个 Role 表，我们可以将这两个表都以直观的方式映射到自定义实体。我们还有一个 UserRoleJoin 表，它代表了 User 与 Role 之间的多对多关系。

然后，我们使用存储过程来获取两个单独的结果：第一个代表 User，第二个代表该用户的 Role：

CREATE PROCEDURE GetUserById(

@UserId INT

)AS

SELECT UserId, UserName, [Password]

FROM Users

WHERE UserId = @UserID

SELECT R.RoleId, R.[Name], R.Code

FROM Roles R INNER JOIN

UserRoleJoin URJ ON R.RoleId = URJ.RoleId

WHERE URJ.UserId = @UserId

最后，我们从关系模型映射到对象模型：

'Visual Basic .NET

Public Function GetUserById(ByVal userId As Integer) As User

Dim connection As New SqlConnection(CONNECTION_STRING)

Dim command As New SqlCommand("GetUserById", connection)

command.Parameters.Add("@UserId", SqlDbType.Int).Value = userId

Dim dr As SqlDataReader = Nothing

Try

connection.Open()

dr = command.ExecuteReader()

Dim user As User = Nothing

If dr.Read() Then

user = PopulateUser(dr)

dr.NextResult()

While dr.Read()

user.Roles.Add(PopulateRole(dr))

End While

End If

Return user

Finally

If Not dr Is Nothing AndAlso Not dr.IsClosed Then

dr.Close()

End If

connection.Dispose()

command.Dispose()

End Try

End Function

//C#

public User GetUserById(int userId) {

SqlConnection connection = new SqlConnection(CONNECTION_STRING);

SqlCommand command = new SqlCommand("GetUserById", connection);

command.Parameters.Add("@UserId", SqlDbType.Int).Value = userId;

SqlDataReader dr = null;

try{

connection.Open();

dr = command.ExecuteReader();

User user = null;

if (dr.Read()){

user = PopulateUser(dr);

dr.NextResult();

while(dr.Read()){

user.Roles.Add(PopulateRole(dr));

}

}

return user;

}finally{

if (dr != null && !dr.IsClosed){

dr.Close();

}

connection.Dispose();

command.Dispose();

}

}

User 实例即被创建和填充；我们转移到下一个结果/选择并进行循环，填充 Role 并将它们添加到 User 类的 RolesCollection 属性中。