这是使用ThenFetch()加载多个集合的正确方法吗? [英] Is this the right way of using ThenFetch() to load multiple collections?

问题描述

我正在尝试使用 NHibernate 3 alpha 1

I'm trying to load all the collections eagerly, using NHibernate 3 alpha 1. I'm wondering if this the right way of using ThenFetch()?

具有复数名称的属性是集合.其他只是一个对象.

Properties with plural names are collections. The others are just a single object.

            IQueryable<T> milestoneInstances = Db.Find<T, IQueryable<T>>(db =>
            from mi in db
            where mi.RunDate == runDate
            select mi).Fetch(mi => mi.Milestone)
                .ThenFetch(m => m.PrimaryOwners)
                .Fetch(mi => mi.Milestone)
                .ThenFetch(m => m.SecondaryOwners)
                .Fetch(mi => mi.Milestone)
                .ThenFetch(m => m.Predecessors)
                .Fetch(mi => mi.Milestone)
                .ThenFetch(m => m.Function)
                .Fetch(mi => mi.Milestone)
                .ThenFetchMany(m => m.Jobs)
                .ThenFetch(j => j.Source)
                ;

我曾想过在 NHibernate论坛中询问此问题，但是很遗憾，禁止访问google网上论坛从我所在的地方.我知道 Fabio 在这里，所以也许NHibernate团队的成员可以对此有所启发? 谢谢

I thought of asking this in the NHibernate forums but unfortunately access to google groups is forbidden from where I am. I know Fabio is here, so maybe the guys from the NHibernate team can shed some light on this? Thanks

推荐答案

显然，在这种情况下，没有使用"ThenFetch"的正确"方法.您的示例运行正常，但生成的SQL包含许多Milestone的联接，并非如此.

Apparently, there's no "right" way to use ThenFetch in such a case. Your example works fine but SQL produced contains many joins to Milestone, which isn't that right.

使用IQueryOver代替IQueryable允许您使用Fetch中的>复杂语法:

Using IQueryOver instead of IQueryable allows you to use complex syntax in Fetch:

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) 

因此，您的情况应该是:

So in your case it would be:

query // = session.QueryOver<X>()
    .Fetch(mi => mi.Milestone).Eager
    .Fetch(mi => mi.Milestone.PrimaryOwners).Eager
    .Fetch(mi => mi.Milestone.SecondaryOwners).Eager
    .Fetch(mi => mi.Milestone.Predecessors).Eager
    .Fetch(mi => mi.Milestone.Function).Eager
    .Fetch(mi => mi.Milestone.Jobs).Eager
    .Fetch(mi => mi.Milestone.Jobs.First().Source).Eager

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