mongoose Aggregation.lookup is not working as expected

[Yaragalla Muralidhar]

The following is my code in App.js. I am using mongoose for communication with mongodb. I am using Mongoose aggregation.lookup for joining two tables and i am not able to get the collection of records. Can somebody tell me what is the problem?

App.js

var catProds = mongoose.model('SV_Catgeory_Products');
var prods = mongoose.model('SV_Products');
var obsr=catProds.aggregate([
    {
        $lookup:
          {
            from: "prods",
            localField: "productId",
            foreignField: "productId",
            as: "inventory_docs"
          }
     }
  ])
  console.log(obsr);

The following is the output:-

Aggregate {
  _pipeline: [ { '$lookup': [Object] } ],
  _model: 
   { [Function: model]
     hooks: Kareem { _pres: {}, _posts: {} },
     base: 
      Mongoose {
        connections: [Object],
        plugins: [],
        models: [Object],
        modelSchemas: [Object],
        options: [Object] },
     modelName: 'SV_Catgeory_Products',
     model: [Function: model],
     db: 
      NativeConnection {
        base: [Object],
        collections: [Object],
        models: [Object],
        config: [Object],
        replica: false,
        hosts: null,
        host: 'localhost',
        port: 27017,
        user: undefined,
        pass: undefined,
        name: 'satvik',
        options: [Object],
        otherDbs: [],
        _readyState: 2,
        _closeCalled: false,
        _hasOpened: false,
        _listening: false,
        db: [Object],
        _events: [Object],
        _eventsCount: 1 },
     discriminators: undefined,
     schema: 
      Schema {
        obj: [Object],
        paths: [Object],
        subpaths: {},
        virtuals: [Object],
        singleNestedPaths: {},
        nested: {},
        inherits: {},
        callQueue: [Object],
        _indexes: [],
        methods: {},
        statics: {},
        tree: [Object],
        _requiredpaths: undefined,
        discriminatorMapping: undefined,
        _indexedpaths: undefined,
        query: {},
        childSchemas: [],
        s: [Object],
        options: [Object],
        '$globalPluginsApplied': true },
     collection: 
      NativeCollection {
        collection: null,
        opts: [Object],
        name: 'sv_catgeory_products',
        collectionName: 'sv_catgeory_products',
        conn: [Object],
        queue: [],
        buffer: true,
        emitter: [Object] },
     Query: { [Function] base: [Object] },
     '$__insertMany': [Function],
     insertMany: [Function] },
  options: undefined }

[Kevin Adistambha]

Hi,

I am using mongoose for communication with mongodb. I am using Mongoose aggregation.lookup for joining two tables and i am not able to get the collection of records. Can somebody tell me what is the problem?

It looks like you didn’t provide a callback to the aggregate() call. Without a callback, it will return the Aggregate object instead. To execute the aggregation, you can either:

• Supply a callback function to the aggregate() call (see http://mongoosejs.com/docs/api.html#model_Model.aggregate)
• Use the aggregate().exec() function (see http://mongoosejs.com/docs/api.html#aggregate_Aggregate-exec)

Please note that for $lookup, you need to know the collection name as stored by MongoDB. Please see http://mongoosejs.com/docs/guide.html#collection for Mongoose collection name options and default.

If you are still having issues, could you post:

• Your MongoDB version.
• Your Mongoose version.
• What you have tried so far, and any error messages.

Best regards,
Kevin

​

[kyse mon mon]

hi do you have one mongoose lookup example source ?

[Kevin Adistambha]

Hi

hi do you have one mongoose lookup example source ?

Please take a look at the example in the mongoose documentation: http://mongoosejs.com/docs/api.html#aggregate_Aggregate-lookup

Best regards,
Kevin

​