Mongodb .NET Driver Nested Array Intersect with Array Value

Question

I have a mongodb collections (docs), for every document (doc1) , I want to find all other documents (doc2) where the intersection of doc2.LinexText[any].Words with doc1.IDs is not empty.

doc {
    "IDs": ["ID1", "ID2"],
    "LineText": [{
        "Words": ["W1", "W2"]
    }]
}

public class MongoDocument : Entity
{       
        public List<string> IDs{ get; set; } = new List<string>();
        public List<LineText> Lines { get; set; } = new List<LineText>();

}

public class LineText
{          
      public List<string> Words { get; set; } = new List<string>();
}

my first attempt was to use below filter but it didn't work (Unsupported filter exception)

var filter = Builders<MongoDocument>.Filter.And(Builders<MongoDocument>.Filter.ElemMatch(x => x.LinesText, x => x.Words.Intersect(mongoDoc.IDs).Any());

I got this exception :

System.ArgumentException: 'Unsupported filter: Any({document}{Words}.Intersect(value(System.Collections.Generic.List`1[System.String]))).'

so for now , I am only matching the first ID until I figure out how to match any ID in the list.

var filter = Builders<MongoDocument>.Filter.And(Builders<MongoDocument>.Filter.ElemMatch(x => x.LinesText, x => x.Words.Contains(mongoDoc.IDs[0]));

how can I perform this intersection using MongoDB .NET Driver ?

Skami · Accepted Answer · 2019-06-11 11:29:54Z

1

You can do this by building an AnyIn filter to represent the intersect like this

   var intersectFilter = Builders<LineText>.Filter.AnyIn(x => x.Words, mongoDoc.IDs);
   var combinedFilter = Builders<MongoDocument>.Filter.ElemMatch(x => x.Lines, intersectFilter);
   var items = collection.Find(combinedFilter).ToList();

This will check if there is any Word that contains the same element as mongoDoc.

answered Jun 11, 2019 at 11:29

Skami

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