映射自定义集合
将我们的关系数据映射到自定义集合的过程与我们对自定义实体执行的过程非常相似。我们不再创建一个实体并将其返回，而是将该实体添加到集合中并循环到下一个：
'Visual Basic .NET
Public Function GetAllUsers() As UserCollection
Dim connection As New SqlConnection(CONNECTION_STRING)
Dim command As New SqlCommand("GetAllUsers", connection)
Dim dr As SqlDataReader = Nothing
Try
connection.Open()
dr = command.ExecuteReader(CommandBehavior.SingleResult)
Dim users As New UserCollection
While dr.Read()
users.Add(PopulateUser(dr))
End While
Return users
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 UserCollection GetAllUsers() {
SqlConnection connection = new SqlConnection(CONNECTION_STRING);
SqlCommand command =new SqlCommand("GetAllUsers", connection);
SqlDataReader dr = null;
try{
connection.Open();
dr = command.ExecuteReader(CommandBehavior.SingleResult);
UserCollection users = new UserCollection();
while (dr.Read()){
users.Add(PopulateUser(dr));
}
return users;
}finally{
if (dr != null && !dr.IsClosed){
dr.Close();
}
connection.Dispose();
command.Dispose();
}
}
我们从数据库中获得数据、创建自定义集合，然后通过在结果中循环来创建每个 User 对象并将其添加到集合中。同样要注意 PopulateUser 映射函数是如何重新使用的。
添加自定义行为
在讨论自定义实体时，我们只是泛泛地提到可以将自定义行为添加到类中。您向实体中添加的功能类型很大程度上取决于您要实现的业务逻辑的类型，但您可能希望在自定义集合中实现某些常见的功能。一个示例就是返回一个基于某个键的实体，例如基于 userId 的用户：
'Visual Basic .NET
Public Function FindUserById(ByVal userId As Integer) As User
For Each user As User In List
If user.UserId = userId Then
Return user
End If
Next
Return Nothing
End Function
//C#
public User FindUserById(int userId) {
foreach (User user in List) {
if (user.UserId == userId){
return user;
}
}
return null;
}
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