Mongoose - Why we make "mongoose.Promise = global.Promise" when setting a mongoose module?
Javascriptnode.jsMongooseJavascript Problem Overview
I'm working with Mongoose. I have seen a lot of developers make the following command:
mongoose.Promise = global.Promise;
Then I was curious to see what is the original value of mongoose.Promise
. I have entered in my editor the following command:
const mongoose = require("mongoose");
console.log("promise: ", mongoose.Promise);
My console returned me :
> promise: function Promise() { [native code] }
Okay, so why make the command mongoose.Promise = global.Promise
since the Mongoose's promise already returns a native code ? I don't understand the point, if someone can help us to understand, would be great,
Thanks
Javascript Solutions
Solution 1 - Javascript
This is legacy code from older examples that isn't needed with Mongoose 5.
Mongoose 4 relied on its own promise implementation, mpromise
. mongoose.Promise
wasn't necessarily Promise
global.
As Mongoose 4 documentation states:
> Mongoose 5.0 will use native promises by default (or bluebird, if native promises are not present) but still support plugging in your own ES6-compatible promises library. Mongoose 5.0 will not support mpromise.
Though the statement about Bluebird is no longer true; Mongoose 5 dropped the support of Node versions that don't have native promises.
mongoose.Promise = global.Promise;
may still be needed if global.Promise
was assigned with another implementation (e.g. Bluebird) after Mongoose was imported, though a better thing would be to assign global.Promise = Bluebird
earlier instead.
Solution 2 - Javascript
Mongoose maintainer here. If you're using Mongoose 5, please remove mongoose.Promise = global.Promise;
. That line was used to address the below deprecation warning with promises in Mongoose 4:
WARNING: Mongoose: mpromise (mongoose's default promise library) is deprecated, plug in your own promise library instead
It does nothing in Mongoose 5. You should only use mongoose.Promise
in Mongoose 5 if you want to use your own promise library with Mongoose, like Bluebird or Q.
There's also a little more about mongoose.Promise
here: https://masteringjs.io/tutorials/mongoose/promise#the-mongoosepromise-property
Solution 3 - Javascript
If we want to use mongoose in different position inside the codes it must be viewed as global mode, that's why we need to set mongoose as :
mongoose.Promise = global.Promise;
Solution 4 - Javascript
we used just in the point when we want to get connected in to MongoDB database :
var mongoose = require('mongoose');
var mongoDB = ' database url ';
mongoose.connect(mongoDB);
mongoose.Promise = global.Promise;
mongoose.connection.on('error',console.error.bind(console, 'MongoDB connection error:'));
you need to create schema and do your own model after
Solution 5 - Javascript
First, mongoose uses Promise for Async applications. In new versions it can be:
mongoose.connect("URL").then("what you need to happen after the connection is done").catch("when the error happened")
Therefore, I used promise and global to use mongoose anywhere as Async when writing mongoose.