Searching in MongoDB: Retrieving a specified number of results with a specific field filter

Currently using MongoDB and in need of assistance with making a query. Specifically, I would like to perform a search on my user collection that includes a field named "country".

For example:

{
    "name" : "John",
    "country" : "FR"
}

For instance, I am interested in retrieving 30 users from France. If there are at least 30 French users in the database, then simply return those 30. However, if there are fewer than 30 (let's say 12) users from France, then I would like to retrieve all 12 French users along with an additional 18 users, regardless of their country of origin, to make up the total of 30.

I am curious whether this can be achieved through a standard query or if I need to resort to utilizing MapReduce.

javascriptmongodbmongodb-query

Answer №1

In my opinion, accomplishing this task in a single query is not feasible.

  • Firstly, retrieve the count of documents with country: "FR".

  • If the count is 30 or more, proceed to fetch exactly 30 documents using the cursor.limit method. However, if the count is less than 30, retrieve all documents where country: 'FR' and then enhance the result by executing an additional query that retrieves documents where country is not equal to FR. This can be achieved using the .apply() function along with the .push method.

    var documentCount = db.collection.count({ "country": "FR" });
var resultSet = [];

if (documentCount >= 30) {
    resultSet = db.collection.find({ "country": "FR" }).limit(30).toArray();
}

if (documentCount < 30 ) { 
    resultSet = db.collection.find({ "country": "FR" }).toArray();
    resultSet.push.apply(resultSet, db.collection.find({ "country": { "$ne": "FR" }}).limit(30-documentCount).toArray());
}

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