Understanding Aliases and Meta-Aliases

Jelly uses model and field aliases throughout. Generally, when naming a field in your model the column in the database has the same name, but Jelly allows most fields to reference a column with a different name. This means you can effectively decouple your database and model schema.

Jelly also has a meta-alias system that allows you to reference specific fields that are common to all models, such as it's primary key.

Aliases

When defining your fields, you can specify a column that this field represents:

class Model_Post extends Jelly_Model
{
    public static function initialize($meta)
    {
        $meta->fields(array(
            'id' => new Field_Primary(array(
                'column' => 'PostId')),
        ));
    }
}

Anywhere you reference the 'id' field, it will be mapped to the 'PostId' column. For example:

$post->where('id', 'IN', array(1, 2, 3));

// The following will work, but ties your logic to 
// your database schema so it's frowned upon
$post->where('PostId', 'IN', array(1, 2, 3));

Anywhere you're referencing a model or field, you should be using the name of a model or field, not the name of a table or column.

Meta-Aliases

Meta-aliases are a syntactic shortcut for referencing a particular field in a model. There are currently four meta-aliases defined:

• :primary_key - references the model's primary key
• :name_key - references the model's name key
• :unique_key - references the model's unique key
• :foreign_key - references the model's foreign key

Example - Using a meta-alias

$post->where(':primary_key', '=', $value);
$post->where(':name_key', '=', $value);

// In this case, value is passed to the unique_key() method in 
// your builder class, which returns the proper field to use
// based on the value
$post->where(':unique_key', '=', $value);

Example - Using the :foreign_key meta-alias

Generally, you want to be able to reference another model's foreign key, so there is a special syntax for doing such a thing.

// Assume a post belongs_to an author
$post->where('post.author:foreign_key', '=', $value);

// This is also possible, though not really useful or practical
$post->where('author:primary_key', '=', $value);

In this case, you specify a model before the meta-alias to pull it from.

Note: Meta-aliases can only be used in the query builder or with the as_array() method in Jelly_Collection.

Changing your meta-aliases

Your model's primary_key, name_key, and foreign_key are all defined in your initialize() method. More information can be found in the API documentation for Jelly_Meta.

The unique_key is a special case since a value is passed to it so that it can determine the proper field to use. To change its behaviour you must create your model specific Jelly_Builder.