Pieces of code I've written while taking 10gen's M101J MongoDB for Java Developers course.

built-in.js

// querying and cursors
cursor = db.people.find(); null ;

cursor.hasNext() // returns true (if there is another set of results) and false (if not)
cursor.next() // returns the next result and move the cursor foward

// Limiting the set of results returned by the queries
cursor.limit(5); null; // limit the results returned by the cursor (default is 20)
// note: the 'null' keyword is used to prevent the mongoshell from printing that query out

// Sorting
cursor.sort( { key : [1, -1] } ); null; // returns sorted results
cursor.sort( { name : -1 } ); null; // returns sorted results in reverse order

// Limiting, sorting and skiping
cursor.sort( { name : -1 } ).limit(3).skip(2); null;
db.scores.find( {type: "exam"} ).sort( { score : -1 } ).skip(50).limit(20);

crud.js

/*
* Inserting, updating, selecting and deleting data from MongoDB
*/

// INSERT
  // fruits collection
  db.fruits.insert( {name : "apple", color : "red", shape : "round", units : 10} )
  db.fruits.insert( {name : "orange", color : "orange", shape : "round", units : 5} )
  db.fruits.insert( {name : "banana", color : "yellow"} )
  db.fruits.insert( {name : "pineapple"} )
  db.fruits.insert( {name : 22} )
  db.fruits.insert( {name: "" } )
  
  // people collection
  db.people.insert( { name : "Mario", hobbies : ["learn new programming languages", "play soccer", "sing"] } )
  db.people.insert( { name : "Luan", hobbies : ["skating", "meet new people", "play soccer"] } )
  db.people.insert( { name : "John", hobbies : ["skating", "play soccer"] } )
  db.people.insert( { name : "Robert", hobbies : ["skating", "sing"] } )
  
  // users collection
  db.users.insert( { name: "David", email : { work : "mario@example.com", personal : "mariosouzaluan@gmail.com" } } )
  db.users.insert( { name: "Norris", email : [ {work : "norris@example.com", personal : "norris@gmail.com"} ] } )

// SELECT
  // findOne
  db.fruits.findOne( {key : "value"}, {key : boolean} )
  db.fruits.findOne( {name : "apple"}, {name : true, _id : false} )
  
  // find
  db.fruits.find()
  db.fruits.find( {color : "red"}, {_id : false, name : true} )
  
  // greater than, less than and/or equals ($gt, $lt, $gte, $lte)
  db.fruits.find( { units : {  $gt : 5 } } )
  db.fruits.find( { units : {  $gt : 5, $lte : 8 } } )
  
  // $exists : returns only records containing specifics keys
  db.fruits.find( { shape : { $exists : true } } )
  
  // $type : returns records matching selected data type
  db.fruits.find( { name : { $type : 2 } ) // 2 = BSON string type
  
  // regex : returns records matching regular expression
  db.fruits.find( { name : { $regex : "e$" } } ) // returns fruits whose name ends with letter 'e'
  db.fruits.find( { color : { $regex : "a" } } ) // returns fruits whose color contains letter 'a'
  db.fruits.find( { color : { $regex : "^y" } } ) // returns fruits whose name begins with the letter 'y'
  
  // $or : takes an array
  db.fruits.find( { $or : [ { name : { $regex : "a" } }, { shape : { $exists : true } } ] } )
  db.fruits.find( { $or : [ { units : { $lt : 20 } }, { score : { $gt : 5 } } ] } )
  
  // $and : takes an array
  db.fruits.find( { $and : [ { name : { $regex : "a"} }, { shape : "round" } ] } )
  
  // querying inside arrays
    // searching for single values
    db.people.find( { hobbies : "play soccer" } )
    
    // $all = stands for AND operand
    db.people.find( { favorites : { $all : [ "play soccer", "skating" ] } } )
    
    // $in = stands for OR operand
    db.people.find( { favorites : { $in : [ "play soccer", "skating" ] } } )
    db.people.find( { name : { $in : [ "Luan", "Mario" ] } } )
    
    // dot notation = search nested documents
    db.users.find( { "email.work" : "mario@example.com" } ) // search inside a nested array field
    db.users.find( { "email.work" : "norris@example.com" } ) // search inside a nested object field