<p>I have a database that contains a table that looks a bit like this:</p>

<p>PropertyId, EntityId, Value</p>

<p>PropertyId and EntityId are a combined primary key. Every Entity is spread over a couple of rows where every row contains a single property of the entity. I have no control over this database so I'll have to work with it.</p>

<p>Is it possible to use NHibernate to map entities from this table to single objects? I only have to read from this table, this might make things a bit easier. Or would I be better off just using DataReaders and do the mapping myself?</p>

Not quite done that, but you could use a custom SQL query to define your entities (distinct entityid, plus any entity level attributes), see
here
.
Although I can see you might want the property/values mapped to attributes of the entity object.  Which might mean further queries to populate them by hand - which may mean your data reader route is best.
If your happy for them to be a collection of the entity then that should be no problem.