Static relations

Currently relationship definitions in AR are defined as non static getters. In reality an AR class represents a table and an instance of that class represents a record.

Relations are defined at the table level, but because AR uses non-static getters our query classes need to instantiate a dummy model for greedy queries.

Requirements for AR relationships:

• One definition for lazy and greedy loading
• Support (cached) retrieval via magic getter
• Support getting a query object (currently via the getter that defines it)

Pros of current approach:

• Uses "native" magic getters (with a small extension)
• Has code completion for the getters since they are normal functions

Cons:

• No way to get the relationships without instantiating a dummy model
• No way to enumerate relations

In Yii1 we had a single function defining the relationships but we also had the dummy model due to lack of late static binding. This allowed for enumeration but had other down sides.

What if, in Yii3 we try to get the best of both? Suppose we define relationships as static functions:

public static function relatedCustomers()
{
    return Has::many (Customer::class, ['id' => 'customer_id']);
}

Internally we would have a sound definition of the relationship, from this we can:

• build a lazy query
• build a greedy query
• enumerate via reflection

From a consumer point of view nothing changes:

• getCustomers via __invoke()
• ->customers via __get()

Pros:

• Relations are now static
• No need for dummy instances
• OO definition of relationship unrelated to the query object

Cons:

• no auto complete for the getter, so could require additional annotations.
• breaks BC

Review the current non-static relationship definitions and the dummy-model path, then trace the proposed static relationship entry point using Has::many(), __invoke(), __get(), and reflection. Done means the requirements for shared lazy and greedy loading, cached magic-getter access, query access, and relation enumeration are resolved without the dummy model.