Unable to understand why the try and catch is not working as expected in mongoose

Question

I am new to mongoose.I am using Sails js, Mongo DB and Mongoose in my project. My basic requirement was to find details of all the users from my user collection. My code is as follows:

try{
    user.find().exec(function(err,userData){
    if(err){
         //Capture the error in JSON format
    }else{
         // Return users in JSON format
     }
    });
   }
catch(err){
      // Error Handling
 }

Here user is a model which contains all the user details. I had sails lifted my app and then I closed my MongoDB connection. I ran the API on DHC and found the following:

1. When I ran the API for the first time on DHC, the API took more than 30 sec to show me an error that the MongoDB connection is not avaliable.
2. When I ran the API for the second time, The API timed out without giving an response.

My Question here why is the try and catch block unable to handle such an error exception effectively in mongoose or is it something that I am doing wrong?

EDIT My Requirement is that mongoose should display the error immediately if the DB connection is not present.

Answer 1

First let’s take a look at a function that uses a synchronous usage pattern.

// Synchronous usage example

var result = syncFn({ num: 1 });

// do the next thing

When the function syncFn is executed the function executes in sequence until the function returns and you’re free to do the next thing. In reality, synchronous functions should be wrapped in a try/catch. For example the code above should be written like this:

// Synchronous usage example

var result;

try {
  result = syncFn({ num: 1 });
  // it worked
  // do the next thing
} catch (e) {
  // it failed
}

Now let’s take a look at an asynchronous function usage pattern.

// Asynchronous usage example

asyncFn({ num: 1 }, function (err, result) {
  if (err) {
    // it failed
    return;
  }

  // it worked
  // do the next thing
});

When we execute asyncFn we pass it two arguments. The first argument is the criteria to be used by the function. The second argument is a callback that will execute whenever asyncFn calls the callback. asyncFn will insert two arguments in the callback – err and result). We can use the two arguments to handle errors and do stuff with the result.

The distinction here is that with the asynchronous pattern we do the next thing within the callback of the asynchronous function. And really that’s it.