Wednesday, 28 June 2017

What is a promise and how to use with mongoose?

What is a promise and how to use with mongoose?

Question: What is a promise?
A promise is an abstraction for asynchronous programming.
It's an object that proxies for the return value thrown by a function that has to do some asynchronous processing.


Question: How does promise work?
The Promise constructor takes a function (an executor) that will be executed immediately and passes in two functions: resolve , which must be called when the Promise is resolved (passing a result), and reject , when it is rejected (passing an error)


Question: Give example of promise work in mongoose?
User.update({id: 100}, {$inc: { views: 1 }}).limit(1).exec();
Here execute multiple function in one line is promise.


Question: How to setup mongoose with promise?
var mongoose = require('mongoose');
mongoose.Promise = require('bluebird');
mongoose.connect('mongodb://localhost:27017/dbname');
var db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function() {
    console.log("MongoDB connected Successfully.!");
});



Question: How to Add the data in mongoDb with mongoose?
//Ajax chat messages
var AjaxChatMessageSchema = mongoose.Schema({
    id: Number,
    userID: Number,
    userName: String,
    userRole: String,
    channel: String,
    dateTime: String,
    ip: String,
    text: String,
    status: String,
    vid: Number
}, {collection: 'ajax_chat_messages'});
var AjaxChatMessage = mongoose.model('ajax_chat_messages', AjaxChatMessageSchema);

var saveData={id:11, userName:'testuser',text:'hello user'}
var AjaxChatMessageDtls = new AjaxChatMessage(saveData);
AjaxChatMessageDtls.save(function(err) {
    if (err) {
        console.log("Error while saving the details");
        response.success = 0;
        res.send(response);
    } else {
        response.success = 1;        
        res.send(response);
    }
});



Question: How to do decrement the value by 1?
AjaxChatMessage.update({id: 100}, {$inc: { views: -1 }}).limit(1).exec();



Question: From where we can read more about promise?
http://mongoosejs.com/docs/promises.html


1 comment :

Anonymous said...

I am getting "DeprecationWarning: Mongoose: mpromise"

Solution:
mongoose uses mpromise which is deprecated. So You can use bluebird as promise.

Example:
var mongoose = require('mongoose');
mongoose.Promise = require('bluebird');
mongoose.connect('mongodb://localhost:27017/dbname');
var db = mongoose.connection;

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