Question

Domain Model I am working on has root aggregate and child entities. Something like the following code:

class Order {    IList<OrderLine> Lines {get;set;} }  class OrderLine { } 

Now I want my Order to control lines. Something like that:

class Order {    OrderLine[] Lines {get;}     void AddLine(OrderLine line); } 

At this time we are using the following pattern:

class Order {    private IList<OrderLine> lines = new List<OrderLine>();    OrderLine[] Lines {get {return this.lines;}}     void AddLine(OrderLine line)    {       this.orders.Add(line);    { } 

NHibernate is mapped directly to the lines field.

Now questions…

• What do you practice in such situations?
• Does anyone use methods: public IEnumerable GetLines()
• What are you using as return type for property? May be ReadOnlyCollection or IEnumerable;
• May be this is not the best place to ask? Suggest please.

Update: Seems IEnumerable wins, however solution still is not perfect…

Answer 1

The pattern I use is:

class Order {    private List<OrderLine> lines = new List<OrderLine>();     IEnumerable<OrderLine> Lines { get { return this.lines; } }     void AddLine(OrderLine line)    {        this.orders.Add(line);    } } 

If you’re using NET 3.5 you get all the search functionality you could want for IEnumerable using LINQ, and you hide your collection implementation.

The problem with returning OrderLine[] is that your collection can be modified externally eg:

Order.Lines[0] = new OrderLine().