Sencha Touch 2.4.2 override validate() to pass model and allow cross-field validation

Model.js

Ext.define('MyApp.override.data.Model', {
    override : 'Ext.data.Model',

    /**
     * @override
     * we want to pass the model (not only config and value)
     */
    validate : function() {
        var errors = Ext.create('Ext.data.Errors'),
            validations = this.getValidations().items,
            validators = Ext.data.Validations,
            length,
            validation,
            field,
            valid,
            type,
            i;

        if (validations) {
            length = validations.length;

            for ( i = 0; i < length; i++) {
                validation = validations[i];
                field = validation.field || validation.name;
                type = validation.type;
                // here we go with the model
                valid = validators[type](validation, this.get(field), this);

                if (!valid) {
                    errors.add(Ext.create('Ext.data.Error', {
                        field : field,
                        message : validation.message || validators.getMessage(type)
                    }));
                }
            }
        }
        return errors;
    }
});

Why
This override is useful if you need to do some cross-field validations (ie a field is valid only if another field has a valid value)

Usage
First add this custom validator:

        Ext.applyIf(Ext.data.Validations, {
            custom : function(config) {
                return config.validator.apply(this, arguments);
            }
        });

Then add to model:

        validations : [{
            field : 'myfield',
            type : 'custom',
            message : 'your custom message',
            validator : function(config, value, model) {
                // do some validation and return true/false
            }
        }]