如何使用LINQ和Entity Framework查询与“AND”条件的多对多关系

Question

My current database solution includes three tables called Establishment , Feature , and a linking many-to-many table called EstablishmentFeature (since an establishment can have many features, and a feature can exists across multiple establishments).

I need to generate a query that returns establishments that meet only certain criteria, namely, which establishments have X features based on a collection of featureId's being passed in. The establishment must have ALL features that are being search, ie. AND not OR condition.

I got the SQL to achieve the desired result, but I am pulling my hair out trying to work out the LINQ (lambra prefereably) equivalent. The T-SQL is:

SELECT e.[EstablishmentId], e.[Name], e.[Description]
FROM Establishment e
INNER JOIN EstablishmentFeature ef
ON e.[EstablishmentId] = ef.[EstablishmentId]
WHERE ef.[FeatureId]  in ('20', '15', '72')
GROUP BY e.[EstablishmentId], e.[Name], e.[Description] 
HAVING COUNT(*) = 3

I tried to use Linqer to convert the SQL but Linqer crashes when it attempts the conversion. I tried reinstalling Linqer, but it crashes without fail when trying to compile the LINQ syntax. (Simpler conversions work though). Also tried to work out the LINQ equivalent using LinqPad, but I just ended up chasing my tail...

Is this something I will have to use PredicateBuilder for? Somewhat exhausted, I don't want to go through the PredicateBuilder learning curve if there is a simple solution that is escaping me.

Answer 1

I'd try this (For all given ids there is any (= at least one) feature that has this given id):

var establishments = context.Establishments
    .Where(e => featureIds.All(fid => e.Features.Any(f => f.FeatureId == fid)))
    .ToList();

( featureIds is an IEnumerable<int> with the Ids being searched for.)