如何使用Node MongoClient查找MongoDB集合中字段的不同值

Question

In my MEAN application, I need to find the distinct values of a field named "DataFields" from my collection "Fixed_Asset_Register", using (non-mangoose) MongoClient:

var mongodb = require('mongodb');

var assert = require('assert');

var MongoClient = mongodb.MongoClient;

MongoClient.connect(url, function (err, db) {
    if (err) {
        console.log('Unable to connect to the mongoDB server. Error:', err);
    } else {
        console.log('Connection established to', url);

        var collection = db.collection('Fixed_Asset_Register');
        var distictDataFieldsValue = ?

}

What is the proper syntax to get back the distinct values of the field named "DataFields"?

Answer 1

I solved this issue using collection.distinct :

collection.distinct("DataFields",(function(err, docs){
            console.log(docs);
            assert.equal(null, err);
            db.close();
        }))

Answer 2

You could also do this by way of aggregation framework . The suitable aggregation pipeline would consist of the $group operator stage which groups the document by the DataFields key and create an aggregated field count which stores the documents produced by this grouping. The accumulator operator for this is $sum .

The next pipeline stage would be the $match operator which then filters the documents having a count of 1 to depict distinction.

The last pipeline operator $group then group those distinct elements and adds them to a list by way of $push operator.

In the end your aggregation would look like this:

var collection = db.collection('Fixed_Asset_Register'),
    pipeline = [
    {
        "$group": {
            "_id": "$DataFields",
            "count": {"$sum": 1}
        }
    },
    {
        "$match": { "count": 1 }
    },
    {
        "$group": {
            "_id": 0,
            "distinct": { "$push": "$_id" } 
        }
    }],
    result = collection.aggregate(pipeline).toArray(),
    distictDataFieldsValue = result[0].distinct;