IQueryable的Linq查询与多个连接在内部级

Question

EDIT: forgot to say I'm using Fluent NHibernate, even though the tag could hint about it anyway.

I have these entity classes:

class OuterLevel
{
    ICollection<MidLevel> mid_items;

    ... other properties
}

class MidLevel
{
    OuterLevel parent;
    Inner1 inner1;
    Inner2 inner2;

    ... other properties
}

class Inner1
{
    int id;
    string description;
}

class Inner2
{
    int id;
    string description;
}

I need to build a Linq query that returns a list of OuterLevel objects with all children populated properly. Supposing all mappings are correct and working, the hard part I'm finding here is that the resulting query should be something like

SELECT * FROM OuterLevelTable OLT INNER JOIN MidLevelTable MLT ON (MLT.parentID = OLT.ID) INNER JOIN
    Inner1Table ON (MLT.Inner1ID = Inner1Table.ID) INNER JOIN
    Inner2Table ON (MLT.Inner2ID = Inner2Table.ID)
 WHERE (Inner1Table.someproperty1 = somevalue1) AND (Inner2Table.someproperty2 = somevalue2)

The main problem is that two joins start from MidLevel object downward the hierarchy, so I cannot figure out which Fetch and FetchMany combination can be used without having the resulting query join two times the MidLevelTable, such as the following does:

  return All().FetchMany(x => x.mid_items).ThenFetch(x => x.inner1).FetchMany(x => x.mid_items).ThenFetch(x => x.inner2);

I would like to return a IQueryable that can be further filtered, so I would prefer avoiding Query and QueryOver.

Thanks in advance, Mario

Answer 1

what you want is not possible because when you filter on the joined tables the resulting records are not enough to populate the collections anyway. You better construct the query in one place to further tune it or set the collection batch size to get down SELECT N+1.