LINQ to SQL many to many int ID array criteria query

问题

Ok this should be really simple, but I am doing my head in here and have read all the articles on this and tried a variety of things, but no luck.

I have 3 tables in a classic many-to-many setup.

ITEMS ItemID Description

ITEMFEATURES ItemID FeatureID

FEATURES FeatureID Description

Now I have a search interface where you can select any number of Features (checkboxes). I get them all nicely as an int[] called SearchFeatures.

I simply want to find the Items which have the Features that are contained in the SearchFeatures.

E.g. something like:

return db.Items.Where(x => SearchFeatures.Contains(x.ItemFeatures.AllFeatures().FeatureID))

Inside my Items partial class I have added a custom method Features() which simply returns all Features for that Item, but I still can't seem to integrate that in any usable way into the main LINQ query.

Grr, it's gotta be simple, such a 1 second task in SQL. Many thanks.

回答1:

The following query will return the list of items based on the list of searchFeatures:

from itemFeature in db.ItemFeatures
where searchFeatures.Contains(itemFeature.FeatureID)
select itemFeature.Item;

The trick here is to start with the ItemFeatures table.

It is possible to search items that have ALL features, as you asked in the comments. The trick here is to dynamically build up the query. See here:

var itemFeatures = db.ItemFeatures;

foreach (var temp in searchFeatures)
{
    // You will need this extra variable. This is C# magic ;-).
    var searchFeature = temp;

    // Wrap the collection with a filter
    itemFeatures =
        from itemFeature in itemFeatures
        where itemFeature.FeatureID == searchFeature
        select itemFeature;
}

var items =
    from itemFeature in itemFeatures
    select itemFeature.Item;

来源：https://stackoverflow.com/questions/3282331/linq-to-sql-many-to-many-int-id-array-criteria-query

标签

linq

arrays

many-to-many