How can I add an instance method to all Models in sails.js?

Question

I'd like to add a default toDisplay function to all models which will use metadata, not unlike attribute/association definitions, to perform manipulations on the instance's attributes/associations making them suitable for display in the UI.

for example:

Foo.findOne(someId)
  .exec(function(err, foo) {
    ...
    res.view({
      foo: foo.toDisplay(),
    });
  });

So, I'd like to add this function too all models. I can imagine a

Model.prototype.toDisplay = ... 

solution, but I'm not sure where to get Model from (some long require('waterline/..../model') path?), and if I had Model, where to put that snip-it.

Please advise.

Behah

OK, let's see if adding more tags gets this more than 12 views in 40 hours (4 of which are mine). – Behah

Answer 1

Model configuration is fully documented here on SailsJS.org. @umassthrower is correct in pointing out that adding an instance method to config/models.js would add it to all of your models; he's also correct in observing that this is not the intended use of the config file.

The reason you're finding this a bit more challenging in Sails than Rails is that Ruby has real classes and inheritance, and Javascript just has objects. One fairly clean way to simulate inheritance and extend your model objects from a "base" object would be to use something like Lodash's _.merge function. For example you could save your base model in lib/BaseModel.js:

// lib/BaseModel.js
module.exports = {

  attributes: {

    someAttribute: 'string',

    someInstanceFunction: function() {
      // do some amazing (synchronous) calculation here
    }

  }

};

Then in your model file, require lodash and use _.extend:

// api/models/MyModel.js
var _ = require('lodash');
var BaseModel = require("../../lib/BaseModel.js");
module.exports = _.merge({}, BaseModel, {

  attributes: {

    someOtherAttribute: 'integer'

  }

};

The attributes from your base model will be merged with MyModel, with MyModel taking precedence.

Setting the first argument to the empty model {} is important here; _.merge is destructive for the first object sent in, so if you just did _.merge(BaseModel, {...} then the base model would be modified.

Also, remember to npm install lodash!

Beatification

That seems like a reasonable approach, and more palatable than adding these to config/models.js. I'll still have to add an additional line to each model, but at least only once and then I'll have that structure in place. I'll give it a try, thanks! – Behah

I'm lazy guy, and if I want to add something to every model, beeing forced to add the same line to every model file really annoys me. -1 - for me it's not answering question - you still need to do something with every single model. – Whereby

Answer 2

In Sails 0.x, when the moduleloader was loaded, you could access to sails.models directly, but now in 1.x this is not ready yet, so, my solution to this was creating a custom hook that wraps the loadModels function of sails.modules, this may not be the best solution but works for me @adam-pietrasiak hope this works for you too :) I am also super lazy when it comes to repeating code.

// provide this code in api/hooks/overrides.js or use another name, who cares

  
const _ = require('lodash');

module.exports = function (sails) {
    return {
        defaults: {},
        savedModelLoad: null,

        configure: function () {
            this.savedModelLoad = this.savedModelLoad || sails.modules.loadModels;
            sails.modules.loadModels = this.loadModelsAndApplyOverrides;
        },

        loadModelsAndApplyOverrides: function(cb){
            this.savedModelLoad(function (err, models) {
                const newModels = _.map(models, applyModelOverrides);

                cb(err, newModels);
            });
        }
    };
};

function applyModelOverrides(model) {
    return _.merge(model, {
      // do your custom stuff here
        attributes: {

            someAttribute: 'string',

            someInstanceFunction: function() {
                // do some amazing (synchronous) calculation here
            }

        }
    });
}

Jitney