Sometimes you have a list of objects (say List<PurchaseOrder>) and you want to get all associated objects (say OrderLines) for all the orders in the list. There are 2 ways of doing this in ECO
- You call a PersistenceService method which takes the list of orders and a string identifying the association name. I don’t like this approach because the name of the association may change during modelling and this wont be picked up as an error until runtime.
- You use the overloaded method which takes an IAssociationEnd. I don’t like this either because you have to find the IAssociationEnd instance from the meta-model at runtime, and to do this you’d probably use a name anyway.
So, what’s the alternative?
public static void EnsureRelatedObjects<T>(this IPersistenceService instance, IEnumerable<T> objects, Expression<Func<T, object>> member) where T : IEcoObject
MemberExpression memberExpression = (MemberExpression)member.Body;
Now you can write code like this
EcoSpace.Persistence.EnsureRelatedObjects(orders, o => o.Lines);
EcoSpace.Persistence.EnsureRelatedObjects(orders, o => o.Customer);
And it will be checked at compile time too.
2 thoughts on “ECO – Ensure related objects”
My implementation varies in 2 ways.
Firstly I don’t like to have persistence related methods on my business classes, whether they are directly implemented or implemented via an extension.
The second difference is that you are ensuring associations for a single object, my method is fetching all associated objects too but uses a list of objects as the source. If I were to implement a single object approach too I’d still not add it to the business object itself 🙂
I like this syntax a bit more:
o.EnsureRelatedObjects(x => x.Lines)
We can easily obtain IPersistenceService from the object itself.