.net – NHibernate IList to List

netnhibernateremoting

Hi I am trying to return a collection of building domain.

private long _id;
private string _buildingName;
private IList<BasicRoom> _rooms;

I am using NHibernate and this mapping for the rooms

<bag name="rooms" table="tb_rooms" lazy="false">
<key column="buildingID"/>
<one-to-many class="Room"/>
</bag>

And I am calling the db like this;

Buildings = (List<Building>)session.CreateCriteria(typeof(Building)).AddOrder(Order.Asc("buildingName")).List<Building>();

The problem is I don't want the _rooms collection to be an IList but I need it to be a List. Alas, NHibernate requires that I use an Interface for collections.
Any idea how to do this. I am new to .Net and thinking that maybe dropping NHibernate might be the way forward. I just need to get the collection typed as an List so I can move on.
Any help much appreciated.

Best Answer

That's not how NHibernate works. You don't get to tell it what the concrete types of your domain model objects are. You only get to tell it what the base types and interfaces are. Then it gets to choose how to implement the domain types efficiently.

For example, NHibernate uses its own internal implementation of IList<T> that knows how to do lazy loading.

Moreover, NHibernate uses its own internal implementation of Building from your domain model. It is not necessarily the case that all the Building objects you will be using with NHibernate will have, as their concrete type, Building. It is only true that they will be Buildings, whether Building is the concrete type of your object, or whether it is the base type of the concrete type of your object.

But this is the right thing to do, since you are supposed to be using interfaces and base types instead of concrete types anyway. NHibernate helps you use all the right approaches to programming.

Now, why do you need a List<Building> per se? Why will IList<Building> not suffice?

Related Solutions

R – How to map a list of strings to the entity using NHibernate

The type of collection to use in your mapping depends on how you want to represent the collection in code. The settings map like so:

The <list> maps directly to an IList.
The <map> maps directly to an IDictionary.
The <bag> maps to an IList. A does not completely comply with the IList interface because the Add() method is not guaranteed to return the correct index. An object can be added to a <bag> without initializing the IList. Make sure to either hide the IList from the consumers of your API or make it well documented.
The <set> maps to an Iesi.Collections.ISet. That interface is part of the Iesi.Collections assembly distributed with NHibernate.

so if you want an IList to be returned, then you would use the <list> mapping. In your case, I'd probably map using the <list> mapping.

R – Convert? Domain objects to DTOs – Cannot create an instance of an interface

Is there any reason the list needs to have a setter? Often, collection properties are read-only - you just Add/Remove/Clear them...

The virtual makes this trickier - normally I'd just do:

public IList<Foo> Foos {get; private set;}
public Bar() { // ctor
    Foos = new List<Foo>();
}

In this case, perhaps (since we don't want to call a virtual method in the ctor):

private IList<Foo> foos;
protected virtual IList<Foo> CreateFooList() {
    return new List<Foo>();
}
public IList<Foo> Foos {
    get {
        if(foos == null) foos = CreateFooList();
        return foos;
    }
}

If this still doesn't work, try a concrete list type.

Best Answer

Related Solutions

R – How to map a list of strings to the entity using NHibernate

R – Convert? Domain objects to DTOs – Cannot create an instance of an interface

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