What is `_type` used for? about mongodm HOT 7 OPEN

'_type' is designed for retrieving a inheritance model.

class Animal {
  public $collection = 'animal';
}

class Mammal extends Animal {}
class Dog extends Mammal {}

$dog = new Dog('name'=>'Lucky');
$dog->save();

When retrieving a model,if we found this model have a parent class,we add '_type' to query params.

Query ['_type'=>'Dog']

$dog = Dog::one();

Query ['_type'=>'Mammal'] , Of course Dog belongs to Mammal,so we must retrieve the right dog .

$mammal = Mammal::one();

So in the db,the document of dog have a '_type' like this: ['Animal','Mammal','Dog']
And this is why '_type' stored as a array() in db.

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And you says right , I also think the current method is not a very good solution . we must have some ways to optimize these code.

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So in short this enables the ability to fetch all documents related to the parent branch.

Functionality

Currently one can take Parent::find() to get all documents which is a child of Parent so considering the following model

class Person extends Model {
  public $collection = 'people';
}

class Faculty extends Person {}
class Tenyear extends Faculty {}
class Visiting extends Faculty {}

class Staff extends Person {}
class IT extends Staff {}
class Tenyear extends IT {}
class Financial extends Staff {}

class Student extends Person {
  public $collection = 'student';
}

one would expect

Person::one() // latest person in or extending Person (i.e. Faculty, Tenyear, Visiting, Staff, IT, etc...)
Faculty::one() // latest person in or extending Faculty
IT::one() // latest person in or extending IT
//....

Issues

• What would one expect with Tenyear::one() I suspect it would fetch all with Tenyear and Faculty.
• If the model has a custom collection like (i.e. Student) then Person::one() would not be able find students.
  • I would say the only way current method wouldn't work as well as solution 2. The only foreseeable solution would be 1.

Possible Solutions

1. Detect Type based on PHP classes rather than Mongo query
   • How would a parent know it's children?
     • Load all models into memory and use foreach(get_declared_classes() as $c) if($c instanceof get_class()) x //...
   • Force convention and build an advanced query using the various children determined by convention
     • Naming convention
       • More restrictive on developer and possible difficult to integrate into existing applications
     • Namespace convention
       • Something like ParentNS/ParentCN
         • i.e. namespace Model/Person/Faculty/Tenyear
2. Store type as hierarchical string using $regex
   • $regex is slow
     • Using /^a.*$/ is efficiently optimized
       • i.e. /^\/Person\/Faculty\/Tenyear.*

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@purekid do you have any more thoughts on this?

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@jrschumacher,i have some ideas but not clear.I will do some test this night at home ,then continue here.

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@purekid Any thoughts about this?

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Also need to consider indexing cost of this. I've been running dex and it seems this has a cost on collections.

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