MongoDB code examples for Montreal.rb presentation // in Javascript

mongodb_at_montreal_rb.js

// Create database - Just use it, it gets created on the fly if it doesn't exist yet
use blog_development;

// Create table - Collections are schema-less, no need to declare a structure.
// They are also created on the fly when you use them
show collections;

// Create index
// Indexing on _id is done automatically by mongoDB
// with the only exception of Capped Collections (more on this later...)
db.articles.ensureIndex( { author_id:1 } );

// Articles may or may not have a title field. Queries will only retrieve documents with a title
db.articles.ensureIndex( { title : 1 }, { sparse : true } );

// users without a first or last name will have these fields set to null
// a duplicate key error will be raised if trying to insert two users with the same first AND last names
db.users.ensureIndex( { first_name: 1, last_name: -1}, {unique: true} ); 

// Indexed fields may be of any type, including documents.
db.articles.ensureIndex( { 'comments.author_id': 1 });   OR   db.articles.ensureIndex({ comments: 1 });

// db.articles.getIndexes(); to check indexes on a collection
// db.system.indexes.find(); to check all existing indexes on the db
// db.articles.find( { title: 'Yet another blog post' } ).explain(); to check what indexes are used

// Insert data
var article = { author_id: ObjectID('4d547108ae7b1cf342000008'),
  created_at : new Date('02/15/2011'),
  title : 'Yet another blog post',
  text : 'Here is the text...',
  tags : [ 'example', 'joe' ],
  comments : [
              { author_id: ObjectID('4d547108ae7b1cf342000010'), comment: 'I disagree' },
              { author_id: ObjectID('4d547108ae7b1cf342000011'), comment: 'Good post' }
  ]
};

// save() works too, although if the document already exists (same _id), it will update it
db.articles.insert( article );    OR      db.articles.save( article );

// Query data
// find all articles
db.articles.find();

// find articles based on the title
db.articles.find( { title: 'Yet another blog post' } );

// find articles based on the author, only fectch the title back
db.articles.find( { author_id: ObjectID('4d547108ae7b1cf342000008') }, { title: 1 });

// find articles commented by their author
db.articles.find( 
  { author_id: ObjectID('4d547108ae7b1cf342000008'),
    'comments.author_id': ObjectID('4d547108ae7b1cf342000008') 
   }, {
    title: 1, 'comments.content': 1
});

// find recent articles with either 
// a title containing 'rails',
// comments containing 'rails', 
// or tagged with 'rails' or 'ruby'
db.articles.find( {
  created_at: { $gte: new Date('01/01/2011') },
  $or: [
       { title: /rails|ruby/i },
       { 'comments.content' : /rails|ruby/im },
       { tags: { $in: [ 'rails', 'ruby' ] } }
  ]
}, { 
  title: 1, created_at: 1, author_id: 1 
}).sort( { created_at: -1, title: 1 } ).skip( 100 ).limit( 10 );

// Will not work !
// Embedded documents cannot (yet) be accessed without going through their parent
db.comments.find( { author_id: ObjectID('4d547108ae7b1cf342000008') });


// JS EVAL
db.articles.find(
   'this.title.match( /ruby/i ) &&
    this.created_at >= new Date("01/01/2011")'
)
db.articles.find({
  published: true,
  $where: "this.title.match( /montreal/i )"
});

// JS Functions
db.articles.find({
  $where: function(){
    return this.tags.length > 3;
  }
});

// Geolocation
// Let's say we have a field with latitude / longitude :
{ location : [ 50 , 30 ] }
{ location : { x : 50 , y : 30 } }
{ location : { foo : 50 , y : 30 } }
{ location : { lat : 40.739037, long: 73.992964 } }

// Create an index on the field 
db.articles.ensureIndex( { location : "2d" } )  
// Same as db.articles.ensureIndex( { location : "2d" } , { min : -180 , max : 180 } )

// Query data based on location
db.articles.find( { location : [50,50] } )
db.articles.find( { location : { $near : [50,50] , $maxDistance : 5 } } ).limit(20)

// Compound indexes
db.articles.ensureIndex( { location : "2d" , tags : 1 } );
db.articles.find( { location : { $near : [50,50] }, tags : 'ruby' } );

// If your world isn't flat
db.articles.find( { location: { $nearSphere : [ 50, 50 ], num: 10) 
db.runCommand( { geoNear : "articles" , near : [ 50 , 50 ], num : 10, spherical: true)



// Capped collections
db.createCollection("log", {capped:true, size:100000}) // max size in bytes
db.createCollection("log", {capped:true, size:100000, max: 100}) // max number of objects




// Counting unique tags with Map Reduce 
      var map = function() {
        if (!this.tags) {
          return;
        }
        for (index in this.tags) {
          emit(this.tags[index], 1);
        }
      };

      var reduce = function(previous, current) {
        var count = 0;
        for (index in current) {
          count += current[index]
        }
        return count;
      };
      db.articles.mapReduce(map, reduce, { out: 'articles_tags_aggregation' });
      



// Update data
db.articles.update( { title: /another blog post/},
  { $set: { title: 'Not just another blog post'}, 
    $addToSet: { tags: { $each: ['atomic', 'awesome' ] } },
    true, // upsert - same as just using save()
    false // update only the first matched document
});

// db.collection.update( criteria, objNew, upsert, multi )
// criteria [ Hash ] the query used to find matching documents
// objNew [ Hash ] updated object or $ operators (e.g., $set) which manipulate the object
// upsert [ Boolean ] if true => update if present, insert if missing - default to false with update() 
// multi [ Boolean ] if all documents matching criteria should be updated, false by default

// $ operators include: 
// $inc, $set, $unset, $push, $pushAll, $addToSet, $pop, $pull, $pullAll, $rename, $bit

db.articles.update( 
   {  _id:ObjectID('4e829472cd7f1cf342000012') , 
      'comments.author_id': ObjectID('4d547108ae7b1cf342000010')
   }, { 
      $set: { 'comments.$.content': 'I completely agree' }
});

// db.runCommand( "getlasterror" ).updatedExisting === true 
// will tell you if your request caused an existing object to be updated
// more on this later...