How to implement MongoDB nested $elemMatch Query in C#

Question

I have a MongoDB collection in the following format.

{
"_id" : ObjectId("56c6f03ffd07dc1de805e84f"),
"Details" : {
    "a" : [
            [ { 
                "DeviceID" : "log0", 
                "DeviceName" : "Dev0"
              },
              { 
                "DeviceID" : "log1", 
                "DeviceName" : "Dev1"
              }
            ],
            [ { 
                "DeviceID" : "Model0", 
                "DeviceName" : "ModelName0"
              },
              { 
                "DeviceID" : "Model1", 
                "DeviceName" : "ModelName1"
              }
            ]
        ]
    }
}

And I am trying to fetch all the documents where the DeviceName in array "a" contains a particular value, say "Name0". However I could get the desired result while using below Mongo query:

db.test_collection.find({"Details.a":{$elemMatch:{$elemMatch:{DeviceName : /.*Name0.*/}}}});

Now I am struggling to implement the above query in C#. Can anyone guide me with that?

so far I have tried the below code and it was not working as expected

query = Query.And(Query.ElemMatch("Details.a", Query.And(Query.ElemMatch("DeviceName", Query.Matches("DeviceName", new BsonRegularExpression("Name0"))))));

Thanks in advance

Saleem · Accepted Answer · 2016-03-01 13:43:02Z

8

Well, honestly writing queries in C# are bit tricky but you can always play a trick.

var bsonQuery = "{'Details.a':{$elemMatch:{$elemMatch:{DeviceName : /.*Name0.*/}}}}";
var filter = MongoDB.Bson.Serialization.BsonSerializer.Deserialize<BsonDocument>(bsonQuery);

var result = col.FindSync (filter).ToList();

I'm deserializing a plain MongoDB queries into a BsonDocument which in return I'm passing to FindAsync as filter.

In the end, you'll have desired outcome in variable result.

Note: I'm assuming MongoDB connection has been established and variable col holds reference to MongoDB collection.

EDIT: Please see following link https://groups.google.com/forum/#!topic/mongodb-csharp/0dcoVlbFR2A. Now it's confirmed that C# driver doesn't support nameless filters so writing above query using Buidlers<BsonDocument>.Filter at moment is not supported.

Long story short, you are left with only one choice and that is to query as I mentioned above in my solution.

edited Mar 1, 2016 at 13:43

answered Mar 1, 2016 at 12:21

Saleem

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1 Comment

Aarthi Priyadharshini Over a year ago

Wow..Great! Thtz exactly the way I want. It worked wonders. Thanx a lot Saleem..:-)

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