Mongoose not calling callbacks of save() and find() - node.js

Question

I'm not getting into the callbacks for either the save() or find() methods. It's also not getting into the callback for mongoose.connect. Any idea why?
Here's my code:
mongoose.connect("mongodb://localhost/blah", {
useMongoClient: true,
}, function (err) {
console.log('connect to database'); // Not called
if (err) {
throw err;
}
});
var Schema = mongoose.Schema
var User = new Schema({
author : String
, type : String
});
var MyUserModel = mongoose.model('User', User); //create and access the model User
var u = new MyUserModel();
u.author = 'authorname';
u.save(function(err){
console.log("saved") // not called
if (err) console.log(err);
});
MyUserModel.find({}, function (err,docs) {
console.log("found"); // not called
console.log(docs);
});

Answer 1

You need to "await" the connection before doing anything. It is an "async" function, and like all async functions you need to await their resolution before continuing other code that depends on the result. In this case the "connection" is going to be needed by later actions with the database.
Best done in modern environments with async/await:
// setup part
var Schema = mongoose.Schema
var User = new Schema({
author : String
, type : String
});
var MyUserModel = mongoose.model('User', User); //create and access the model User
// async parts - wrapped in a self executing closure with the async keyword
(async function() {
try {
const conn = await mongoose.connect("mongodb://localhost/blah", {
useMongoClient: true,
});
console.log('database connected');
// Add a user and wait for it to save
var u = new MyUserModel();
u.author = 'authorname';
await u.save();
console.log("saved");
// find the documents and await that too
let docs = await MyUserModel.find();
console.log(JSON.stringify(docs,undefined,2));
} catch(e) {
console.error(e);
} finally {
mongoose.disconnect();
}
})();
Or by chaining promises in older nodejs versions:
// setup part
var Schema = mongoose.Schema
var User = new Schema({
author : String
, type : String
});
var MyUserModel = mongoose.model('User', User); //create and access the model User
// Async part
mongoose.connect("mongodb://localhost/blah", { useMongoClient: true })
.then( () => {
var u = new MyUserModel();
u.author = 'authorname';
return u.save();
})
.then( () => MyUserModel.find() )
.then( docs => {
console.log(JSON.stringify(docs,undefined,2));
mongoose.disconnect();
})
.catch( e => console.error(e) );
Bottom line is that you need to wait for completion of all async calls and .connect() is now an async call in modern mongoose releases. It really should have always been handled like this, but now you "must" handle like this.