Make 'reserved keywords' in validations extendable

[mphasize]

This PR relates to #444:

I think the "ignored property keys" in waterline/core/validations should be exposed and extendable by an application developer. That would make it easier to write custom blueprints with specialized model definitions.

Example: I am using an async keyword in my model attributes to define which associations I want to have populated by default and which should be excluded by default. My customized blueprints handle this attribute, but I have to modify waterline/core/validations to prevent it from choking on the async property.

Now I modified the waterline core a little bit, to make the default keywords in core/validations extendable through setting a configuration object in sails.config.models. More info below.

However, after doing all the work, I came back and read about the custom types that waterline allows and now I am wondering just how different the use cases and possible benefits for each approach are.

Comments welcome!

---

Configuration option

In config/models I am adding a configuration key "validations" like this:

// These properties should be ignored in Waterline validations
validations: {
  ignoreProperties: [ 'async', 'special']
}

Changes in waterline core

In waterline/core/index.js I make sure that the configuration gets passed down to the initializer function of the Validator:

this._validator.initialize(_validations, this.types, this.defaults.validations); // extend the initializer

After that I modified waterline/core/validations.js to accept the config and concatenate any keywords in ignoreProperties to the reservedProperties.

this.reservedProperties = ['defaultsTo', 'primaryKey', 'autoIncrement', 'unique', 'index', 'collection', 'dominant', 'through',
        'columnName', 'foreignKey', 'references', 'on', 'groupKey', 'model', 'via', 'size',
        'example', 'validationMessage', 'validations', 'populateSettings', 'onKey', 'protected'];

if(defaults.ignoreProperties && Array.isArray(defaults.ignoreProperties)) {
  this.reservedProperties = this.reservedProperties.concat(defaults.ignoreProperties);
}

....

  // If property is reserved don't do anything with it
  if(self.reservedProperties.indexOf(prop) > -1) return;

Test

Added a unit test for this behaviour to be found in test/unit/validations/validations.ignoreProperties.js.

[mphasize]

To elaborate on my own question:
Using custom types, it looks like we have to define the types per model. So there's a potential drawback, that we have to repeat ourselves over and over. Also, custom types pass through the validator which adds a few function calls. On the other hand, this way it's actually possible to use the validator.

The modification to extend the reserved properties allows us to use a global configuration across all models and it simply skips validation on those keywords, potentially saving a few processor loops.

To ask a new question: Is it possible to define custom types globally in Sails?