atlas/orm

A data mapper ORM for your persistence model (not your domain model).

2.0.0 2017-10-17 12:38 UTC

README

No annotations. No migrations. No lazy loading. No data-type abstractions.

Atlas is a data mapper implementation for persistence models (not domain models).

As such, Atlas uses the term "record" to indicate that its objects are not domain objects. Use Atlas records directly for simple data source interactions at first. As a domain model grows within the application, use Atlas records to populate domain objects. (Note that an Atlas record is a "passive" record, not an active record. It is disconnected from the database.)

Atlas is stable for production use. Please send bug reports and pull requests!

Documentation is at http://atlasphp.io.

Rationale

(Or, "Why does Atlas exist?")

Atlas helps developers to get started about as easily as they would with Active Record for their persistence model, and provides a path to refactor more easily towards a richer domain model as needed.

Atlas uses a table data gateway for the underlying table Rows, then composes those Rows into Records and RecordSets via a data mapper. Simple methods can be added, as they become necessary, to the Record and RecordSet persistence model objects. (Rows do not have behavior.) The domain logic layer (e.g. a service layer, application service, or use case) can then manipulate the Record objects.

A persistence model alone should get the appplication a long way, especially at the beginning of a project. The Row, Record, and RecordSet objects are disconnected from the database, which should make the refactoring and integration process a lot cleaner than with Active Record.

As a domain model grows within the application, Mehdi Khalili shows that the refactoring process can then move along one of two paths:

  • "Domain Model composed of Persistence Model". That is, the domain objects use Atlas persistence model Record objects internally, but do not expose them. The domain objects can manipulate the persistence model objects internally as much as they wish. For example, a domain object might have a getAddress()method that reads from the internal Record.

  • "DDD on top of ORM". Here, Repositories map the persistence model objects to and from domain objects. This provides a full decoupling of the domain model from the persistence model, but is more time-consuming to develop.

Finally, Atlas supports composite primary keys and composite foreign keys. Performance in these cases is sure to be slower, but it is in fact supported. (For some legacy systems, composite keys are absolutely necessary.)

Other rationalizations, essentially based around things not desired:

  • No annotations. (Code should be in code, not in comments.)

  • No migrations or other table-modification logic. Many ORMs read the PHP objects and create, or modify, tables from them. Atlas, on the other hand, is a model of the database, not a creator of it. (If migrations are needed, use a tool specifically for migrations.)

  • No lazy-loading. Lazy-loading is seductive, but eventually is more trouble than it's worth. Atlas doesn't make it available at all, so it cannot be invoked accidentally.

  • No data-type abstractions. Data-type abstraction seems great at first, but it too ends up not being worth the trouble. Therefore, the actual underlying database types are exposed and available as much as possible.

Possible deal-breakers for potential users:

  • Atlas uses code generation, though only in a very limited way. It turns out that code generation is useful for building the SQL table classes. Each table is described as a PHP class, one that returns things like table name, column names, etc. This is the only substantial class that gets generated by Atlas; the others are empty extensions of parent classes.

  • Atlas uses base Row, Record, and RecordSet classes, instead of plain-old PHP objects. If this were a domain modeling system, a base class would be unacceptable. Because Atlas is a persistence modeling system, base classes are less objectionable, but for some this may be undesired.