How to filter a array element in c# mongo db driver

Question

I have array in a document like this

 {
    "samples": [
        [
            25,
            "1535530415"
        ],
        [
            "45",
            "1535530415"
        ]
    ]
}

and i try to fetch the value based on second value of each array

my filter query is

 var collection = database.GetCollection<BsonDocument>("History");
        FilterDefinition<BsonDocument> filterDefintion = null ;
        ProjectionDefinition<BsonDocument> project = Builders<BsonDocument>.Projection.Include("samples").Exclude("_id");
        filterDefintion =  Builders<BsonDocument>.Filter.Eq("samples[1]","1535530415");

but it getting an empty array.how to filter the array values in mongo c# driver.

mickl · Accepted Answer · 2018-11-23 18:55:56Z

2

Your sample document contains an array of arrays. To reference item at index 1 you can take advantage of the fact that in JS an array can be considered as an object where indexes are the properties, so in your case what you're storing can also be interpreted as:

{
    "samples": [
        {
            "0": 25,
            "1": "1535530415"
        },
        {
            "0": 45,
            "1": "1535530415"
        }
    ]
}

knowing that you can use $elemMatch to reference the right element:

db.History.find({ "samples": { $elemMatch: { 1: "1535530415" } } })

or in C# code:

filterDefintion = Builders<BsonDocument>.Filter.ElemMatch<BsonDocument>("samples", new BsonDocument() { { "1", "1535530415" } });

answered Nov 23, 2018 at 18:55

mickl

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3 Comments

leo Martin Over a year ago

mickl is it possible to check the key (ex "0" ) is present or not?

mickl Over a year ago

@arunthomas sure, you can use $exists operator, like: db.History.find({ "samples": { $elemMatch: { 1: "1535530415" } }, "samples.1": { $exists: true } })

leo Martin Over a year ago

in C# code: Builders<BsonDocument>.Filter.Exists("0");

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