NHibernate 3. Alternatives to “ThenFetch” in QueryOver

ε祈祈猫儿з 提交于 2019-12-03 09:13:04

问题


I'm using NHibernate 3.0 with both the LINQ provider and QueryOver. Sometimes I want to eager load related data, and there comes the method "Fetch" to the rescue, both in LINQ and QueryOver. Now I have a special scenario where I want to eager load a property not directly on the second level, like:

Foo f = ...;
f.A.B.C

with LINQ there's no problem, as you can "chain" fetches with the method "ThenFetch", like:

var result = Session.Query<Foo>().Fetch(a => a.A).ThenFetch(b => b.B).ThenFetch(c => c.C).ToList();

In QueryOver there's no such method, so how can I achieve the same result?

Thanks in advance.


回答1:


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).




回答2:


Just as a curiosity, I'll post the reply they gave me on the NHibernate Jira:

query 
    .Fetch(p => p.B) 
    .Fetch(p => p.B.C) // if B is not a collection ... or 
    .Fetch(p => p.B[0].C) // if B is a collection ... or 
    .Fetch(p => p.B.First().C) // if B is an IEnumerable (using .First() extension method) 



回答3:


I think you can do that with JoinQueryOver

IQueryOver<Relation> actual =
   CreateTestQueryOver<Relation>()
    .Inner.JoinQueryOver(r => r.Related1)
    .Left.JoinQueryOver(r => r.Related2)
    .Right.JoinQueryOver(r => r.Related3)
    .Full.JoinQueryOver(r => r.Related4)
    .JoinQueryOver(r => r.Collection1, () => collection1Alias)
    .Left.JoinQueryOver(r => r.Collection2, () => collection2Alias)
    .Right.JoinQueryOver(r => r.Collection3)
    .Full.JoinQueryOver(r => r.People, () => personAlias); 


来源:https://stackoverflow.com/questions/4801235/nhibernate-3-alternatives-to-thenfetch-in-queryover

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