Support service initialization (boot method)

[LoicPoullain]

Issue

Sometimes services need a special method to initialize themselves. In the case of session stores, this method could be use to establish a connection to the database (redis, TypeORM, etc) instead of using lazy loading.

Constructors are not appropriate in this case because:

• They do not support async operations.
• Sub-dependencies are not accessible inside the constructor.
• Unit testing is made harder.

Solution

Allow to add a boot method (sync or async) in each service. These methods will be executed (if they exist) after all the services have been instantiated and before AppController.init gets called (if init exists). No assumption can be made in which order the boot methods are called.

Notes on implementation

• Be careful with instances injected manually (TypeORM connections, repositories, etc) (feat(Core/createApp): Augment createApp to allow optionally passing ServiceManager object #599)
• Add a method ServiceManager.getAndBootOnce for special cases.
• In the ServiceManager, services must initialized only once.

Related issues

#627 #598 #516 #538

[LoicPoullain]

Released with v1.8