How Does Junction Work

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Junction decorates your functions and prototypes dynamically. It's like aspect-oriented-programming. The decorating happens at the moment when you give Junction any meta information or declarations about your application.

For example, let's take a look at the code for a sample Milestone model object, which could be part of a Project-Milestone tracking application...

function Milestone() {}

modelInit('Milestone');

Milestone.belongsTo('Creator',  { modelName : 'Person' });
Milestone.belongsTo('Domain',   { modelName : 'Org' });
Milestone.belongsTo('Project');
Milestone.belongsTo('Assignee', { modelName : 'Person' });

Milestone.hasMany('Messages');
Milestone.hasMany('TodoLists');

Milestone.findRecentByProject = function(projectId, date) {
    return Milestone.find('all', {
      conditions: [ "Milestone.project_id = ? AND Milestone.created_at > ?",
                    projectId, date ] });
}

When '''modelInit()''' is invoked, Junction knows that the Milestone function is to be a model object in the Model-View-Controller sense. The '''modelInit()''' function performs the following...

• It associates the model name string 'Milestone' with the Milestone function.
• It assumes the plural name is 'Milestone' + 's', or 'Milestones'.
• This is overridable using the pluralName() function.
• It assumes the database table name is 'Milestone'.
• This is overridable using the tableName() function.
• It adds some functions or methods to the Milestone function object, such as...
• Milestone.find()
• Milestone.findActive()
• Milestone.findAll()
• Milestone.findFirst()
• Milestone.findBySql()
• Milestone.newInstance()
• You should use "m = Milestone.newInstance()" instead of "m = new Milestone()" when creating instances of the Milestone.
• It also adds some functions or methods to the Milestone.prototype object, to give each Milestone instance object extra functionality, such as...
• save()
• updateAttributes()
• destroy()
• For example, you can now invoke "m.save(); m.destroy();".

Back to the sample Milestone code, when the '''belongsTo()''' declaration function is called, it adds even more functions to the Milestone's prototype object. For example, when ''belongsTo('Creator', { modelName : 'Person' })'' is invoked, the following happens...

• It adds a getCreator() function or method to Milestone.prototype.
• It remembers that the associated model object is the function named 'Person', instead of the normally guessed default name which would have been a function named 'Creator'.
• The options can be set through the second paramater hash object to '''belongsTo()''', includes...
• modelName
• foreignKey

Similarly, when the '''hasMany()''' declaration function is called, such as ''hasMany('Messages')'', Junction adds methods to the Milestone.prototype object such as getMessages().

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