[MongoDB] Query, update, index and group

/*1. Query Operators*/Db.posts.find ({viewscount: {$get:$lte: 3000}}, {_id:0, Viewscount:1, title:1})//$inDb.posts.find ({categories: {$inch: [' iOS ']}}, {categories:1})//$whereDb.posts.find ({$where:function(){        return  This. categories.length>15}}, {categories:1, Title:1})//See how many categories from previous query:Db.posts.find ({$where:function(){        return  This. categories.length>15}}, {categories:1, title:1}) [0].categories.length

Update:

/*     2. Update*/var d = db.posts.findOne (); // Change the author email:d.author.email = "[email protected]"//Update the database  Db.post.update ({_id:d._id}, d); // Update Mutli-document True}}, {multi:true//Add new key, set Mutli

Performance and Indexes:

/*3. Performance and Indexes*///Create the DataDb.numbers.drop ();varnum = 5000000, I= 0;  for(i = 0; i < num; i + +)){    varRandomnumber = Math.floor (Math.random () *10000);    Db.numbers.insert ({number:randomnumber}); //print (i);}db.number.find ({number: {$gt:$LT: +}, {_id:0, number:1}}). explain ();//It scan all the doucment, took 3500ms //Add Index:Db.numbers.ensureIndex ({number:1});//took 1046 MS, scan 1m instead of 5m

Group:

/*     4. $group*//sum up the Viewcount, rename the result as ' Totalviewscount '  Db.posts.aggregate ({    $group: {        _id:null,        ' $viewsCount '}}    })  //adding 1 for each documentdb.posts.aggregate ({    $group: {        _id: NULL ,         1}}    )//  =Db.posts.count ()

[MongoDB] Query, update, index and group