Linq – Tradeoffs using NHibernate 3.0 QueryOver or LINQ provider

linqnhibernate

I have not found a clear comparison of what is supported with the NHibernate 3.0 LINQ Provider compared to using the QueryOver syntax. From the surface, it seems like two large efforts into two very similar things.

What are the key trade offs to using each?

Best Answer

LINQ and QueryOver are completely different query methods, which are added to the ones that existed in NHibernate 2 (Criteria, HQL, SQL)

QueryOver is meant as a strongly-typed version of Criteria, and supports mostly the same constructs, which are NHibernate-specific.

LINQ is a "standard" query method, which means the client code can work on IQueryable without explicit references to NHibernate. It supports a different set of constructs; it would be hard to say if there are more or less than with QueryOver.

My suggestion is to learn all the supported query methods, as each use case is different and some work better with one, some work better with other.

Related Solutions

Linq – NHibernate 3.0: No FirstOrDefault() with QueryOver

I have now found out that I could use the Take() extension method on the IQueryOver instance, and only the enumerate to a list, like so:

Result precedingOrMatchingResult = Session.QueryOver<Result>().
        Where(r => r.TimeStamp < timeStamp).
        OrderBy(r => r.TimeStamp).Desc.   
        Take(1).List(). //enumerate only on element of the sequence!
        FirstOrDefault(); //get the preceding or matching result, if there is any

NHibernate 3. Alternatives to “ThenFetch” in QueryOver

I actually managed to solve this problem using two different approaches:

Approach one:

Session.QueryOver<Foo>().Fetch(x => x.A).Fetch(x => x.A.B).Fetch(x => x.A.B.C)

Approach two:

A a = null;
B b = null;
C c = null;

Session.QueryOver<Foo>()
    .JoinAlias(x => x.A, () => a)
    .JoinAlias(() => a.B, () => b)
    .JoinAlias(() => b.C, () => c)

Both work (altough I'm not exactly sure if one of them generated "inner" and the other one "outer" joins).

Best Answer

Related Solutions

Linq – NHibernate 3.0: No FirstOrDefault() with QueryOver

NHibernate 3. Alternatives to “ThenFetch” in QueryOver

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