Winston Logging with Mongoose Docs

Question

Winston Logging with Mongoose Docs

I recently just switched over to Winston for logging and noticed an issue when logging mongoose docs after an exec.

Example:

Model.find().exec(function (err, docs) {
    console.log(docs) // Prints the collection fine
    winston.info(docs) // Prints a ton on mongoose stuff, related to the query
});

So basically how do I get winston logging to print the same way as you get from console.log? I'm guessing it must how it is being serialised before being logged by calling toJSON().

Do I have to manually call .toJSON() each time or have people done something else to make this work automatically?

node.js
mongoose
winston

Answer 1

Warning

I think the intended use of winston is to log string messages in first place and (if needed) additional meta information. Moreover, I do not quite get why you would like to log the whole collection returned from mongo and not - let say - just _ids (assuming docs may be pretty big).

Intro

I looked into winston source and here are relevant parts:

winston/logger.js

Logger.prototype.log = function (level) {
  var self = this,
      args = Array.prototype.slice.call(arguments, 1);

  ...

  var callback = typeof args[args.length - 1] === 'function' ? args.pop() : null,
      meta     = typeof args[args.length - 1] === 'object' ? args.pop() : {},
      msg      = util.format.apply(null, args);

  ...

}

Basically, single argument of type object is interpreted as the meta. Console transport layer (default) is mainly defined in winston/common.js and here is how meta is handled:

 ... if (Object.keys(meta).length > 0) {
      output += ' ' + (
        options.prettyPrint
          ? ('\n' + util.inspect(meta, false, null, options.colorize))
          : exports.serialize(meta)
      );
    }

serialize method iterates (recursively) over all keys of an object to form the final string (instead of calling .toString or similar).

Proposed Solutions

Both solutions force winston to interpret a single object argument not as meta but as the message string.

If you want to support different transport layers than they have to be modified.

Change winston source-code

Just fork the repo and make relevant changes to the source code. There is plenty of ways to accomplish it. One ugly could be:

 meta     = args.length === 1 ? {} :
          (typeof args[args.length - 1] === 'object' ? args.pop() : {}),

But much better would be to add special case in the .serialize method make special treatment if the object is mangoose model, very naive and incorrect:

 else if ('_doc' in obj && 'save' in obj){
        var result = [];
        msg += '{'
        for(var key in obj['_doc']){
            result.push (key + ':' + obj['_doc'][key]);
        }
        msg += result.join(', ');
        msg += '}';
    }

(Unfortunately there is a problem with this approach, as winston makes copy of the meta and all methods defined higher in prototypical chain are lost -- otherwise it would as easy as calling obj.toJSON and for sure it would be the most elegant and robust solution)

Override winston default behaviour

var original = winston.log;
winston.log = function(){
    if(arguments.length === 2){
        original.call(winston, arguments[0], arguments[1], {});
    }
    else {
        original.apply(winston, arguments);
    }
}

Explanation: arguments[0] defines level so arguments[1] is the actual object to be logged.