Getting Data with Queries

Embedded document

A document is like a row of data. It consists of a key-value pair of the data. An embedded document is a document with a value that’s a field in another document.

  {
     "name" : "John Doe"
     "age" : 24,
     "education" : {
        "primary": "St Lukes",
        "secondary": "Federal Govt College",
        "tertiary" : "University of Ilorin"
    }
  }

The education field of the top document (object) above is an embedded document. Dot notation is used when querying for an embedded document.

What’s a query?

A query in MongoDB is the way data is retrieved from the database. A query statement could be used to retrieve all data in a collection, or it can contain criteria that restricts the retrieved data.

Query structure in MongoDB

A query in MongoDB usually takes the form of the following:

 db.collectionName.find()

Or:

 db.collectionName.findOne()

Meteor MongoDB API for querying MongoDB is slightly different because it takes this form:

 Mongo.Collection.find()
//or
 Mongo.Collection.findOne()

Meteor MongoAPI find returns a reactive cursor that reruns when dependencies change, while findOne returns a single document. To pull data out of a cursor, we append the fetch() method at the end.

 Mongo.Collection.find().fetch()
//or
 Mongo.Collection.findOne()

The difference between how we query for data in Meteor API and MongoDB is the chaining of the fetch() method used to pull data from a cursor.

Mongo.Collection.findOne(selectors, options)

The code above finds the first document that matches a selector.

Common MongoDB query operators