Mongoose by Examples

mongoose-examples.js

/*
Stream / QueryStreams
----------------------------
Ref: http://mongoosejs.com/docs/api.html#querystream_QueryStream

one chunk == one document

*/

readable = Model.where('created').gte(twoWeeksAgo).stream();
readable = Model.find().stream({ transform: function(doc){
  return  JSON.stringify(doc);
}});

readable
  .on('data',function(doc){
    console.log(doc.toObject())
  })
  .on('error',function(){})
  .on('close',function(){})
  .pipe(writable)

/*
Get the first matching element in an Array:
---------------------------
Ref: http://docs.mongodb.org/manual/reference/operator/projection/positional/#proj._S_

Check limitation: only one array field allowed.
*/
Project.find({'majorsector_percent.Percent': 70}, {_id:0,'majorsector_percent.$':1},function(err,docs){
  console.log(docs)
})


*/


/*
Select embedded array or nested array fields as top-level document
-------------------------------------------------------------------
Example Schema:

{
  name: String,
  states: [{
    name: String,
    cities: [{
      name: String,
      schools: [{
        name: String,
        addresss: String
      }]
    }]
  }]
}

ref: 
*/

//get a city as a top-level document:
Country.aggregate([
    //match by city _id and reduce the no of documents for the next pipeline stages
    {$match : {'states.cities._id': "55bab42fb768129caa039b4b" } },
    //deconstruct states array
    {$unwind: '$states'},
    //deconstruct cities array
    {$unwind: '$states.cities'},
    //match again in the deconstructed document list
    {$match : {'states.citites._id': "55bab42fb768129caa039b4b" } },
    //project the fields
    {$project : 
      {     
        _id: "$states.cities._id",
        name: "$states.cities.name",
        schools : "$states.cities.schools"
      }
    }
])


/*
Group by a key and return the first document from each group:
*/

db.zips.aggregate(
   [
     {
       $sort: { state: 1, city: 1 }
     },
     {
       $group:
         {
           _id: "$state",
           city: { $first: "$$CURRENT" }
         }
     },
     {
        $project : 
          {     
            _id: "$city._id",
            city: "$city.city"
          }
    }
   ]
)