summer

A very simple straightforward IOC/DI container

npm install summer
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summer

Summer is a very simple straightforward IOC/DI container. It was developed with the goal in mind to define application contexts and resolve multiple asynchronous resources with their dependencies with ease.

Basic usage

Root context

The root context, as its name implies, is a basic context without parent context.

Initialize a root context:

Summer = require "summer"
rootContext = new Summer

Scoped context

A scoped context is an optionally named context with a parent context.

The scoped context is the place were scoped locals and scoped objects are registered in (except "singleton" scoped objects, they are stored in the root context).

Initialize a scoped context:

requestContext = new Summer(rootContext, "request")

Get root context and scoped contexts:

childContext.parent #=> returns the parent context
childContext.root() #=> returns the root context
childContext.context("request") #=> returns the context with name `request`

Register initializer

There are two ways to register an initializer, either by register a class or an initializer function.

Summer::register can be called as follow:

register(id, initializer_function)
register(id, array_of_arguments, initializer_function)
register(id, options, initializer_function)
register(id, options)

Possible options are:

  • initializer: The initializer function (can be supplied as second or third argument)
  • class: Class to initialize (only when no initializer is supplied)
  • args: Array of arguments for initializer/constructor
  • properties: Object with properties to set on initialized object
  • init: Function or name of an instance method to call after properties are set.
  • dispose: Function or name of an instance method to call after deleting the resolved object from scope (only useful for scoped objects).

The "init" and "dispose" callbacks will be called with a callback function if the arguments length is greater than 0.

Register a class:

c.register "fooService", class: FooSevice

Register a class with constructor arguments:

c.register "fooService", class: FooSevice, args: [c.ref("db"), 5]

Summer::ref returns a reference to a registered service ("db" in this example). This reference will be resolved and supplied as first constructor argument, the second constructor argument will be 5.

Register a class with properties:

c.register "fooService",
  class: FooSevice
  properties:
    db: c.ref("db")
    maxConnections: 5

This properties will be applied after constructing the class. For an explanation of "c.ref" see the example above.

Register an initializer:

c.register "db", (callback)->
  db = new DB(...)
  db.open (err, db)->
    callback(err, db)

or

c.register "db", 
  initializer: (callback)-> ...

Register an initializer with arguments:

c.register "usersCollection", [c.ref("db")], (db, callback)->
  db.collection "userCollection", (err, collection)->
    callback(err, collection)

or

c.register "usersCollection", { args: c.ref("db") }, (db, callback)-> ...

or

fs = require "fs"
c.register "configFile", { args: __dirname + "/../config.json" }, fs.readFile

Register an initializer with multiple arguments:

c.register "userController", ["userCollection", "commentCollection"], (users, comments, callback)->
  callback(null, new UserController(users, comments))

Register an initializer with a dispose method:

c.register "db",
  initializer: (callback)->
    db = new DB(...)
    db.open (err, db)->
      callback(err, db)
  dispose: "close" # same as (db)-> db.close()

Resolve objects

Summer can resolve one or more objects at once.

Resolve one object:

c.resolve "serviceId", (err, service)-> ...

Resolve multiple objects:

c.resolve ["serviceOne", "serviceTwo"], (err, services)->
  doSomething services.serviceOne
  doSomething services.serviceTwo

Resolve multiple objects with an alias to id map:

c.resolve foo: "serviceOne", bar: "serviceTwo", (err, services)->
  services.foo #=> serviceOne
  services.bar #=> serviceTwo

Manually resolve an object from an initializer

If you like to resolve an object manually from inside your initializer function, it is important to do this with the method "resolve" on the current binding (this or @) and not with "resolve" on your context object, otherwise the cyclical dependency detection won't work.

Scoped locals

The context/scope acts like an "inheritable" map where "get" and "has" goes backwards up the ancestor chain of the scope to find a value. The methods "set" and "delete" will operate on the current scope and shadow values from ancestor scopes.

For example:

context.set "foo", "bar"
childContext.has "foo" #=> true
childContext.get "foo" #=> "bar"
childContext.set "foo", "baz"
childContext.get "foo" #=> "baz"
context.get "foo" #=> "bar"
childContext.delete "foo"
childContext.get "foo" #=> "bar"

Scoped objects

Scoped objects are objects which are singletons in their scope. The scope option can be any name of an existing named scope. Special scopes are "prototype", which is not registered on any scope and "singleton", which is registered on the root context. If no scope option is given "singleton" is assumed.

Prototype scope example:

c.register "fooService", class: FooSevice, scope: "prototype"

Request scope example:

c.register "fooService", class: FooSevice, scope: "request"

Middleware

The Summer::middleware method returns a Connect middleware which wraps the context in a request scope on every request. It calls shutdown on the request scope after calling "res.end". It sets the newly created context on "req.context".

For example:

app.use applicationContext.middleware([name="request"])
app.use (req, res)->
  doSometing req.context
  res.end("ok") #=> will shutdown the previously created request context (req.context)

Events

The Summer container extends Nodes events.EventEmitter. Three events are emitted by Summer:

  • initialized: After resolving the object. The listener signature is (container, factory, object).
  • dispose: During disposing the object, triggered by Summer::dispose. The listener signature is (container, factory, object).
  • shutdown: During shutting down the container, triggered by Summer::shutdown. The listener signature is (container).

Hooks

The hooks are interceptor callbacks, allowing the application to inspect and/or manipulate resolved objects during their life cycle.

Registration of a hook

Summer.addHook "afterPropertiesSet", (factory, instance, callback)->
  if typeof instance.afterPropertiesSet is "function"
    instance.afterPropertiesSet()
  callback()

Summer has three life cycle phases:

  • afterInitialize: Is called after resolving the object and before setting its properties.
  • afterPropertiesSet: Is called after resolving and setting properties on the resolved object, this is called independently of defining properties for a registry entry (provided by the "resolveAndSetProperties" hook).
  • dispose: Is called after removing the resolved object from scope.

Included hooks

Summer comes with predefined and pre-registered hooks to extend its basic functionality:

  • Summer.Hooks.autowired: Checks the class/initializer for "autowire" annotations and process them.
  • Summer.Hooks.disposableEntity: Handles the factories "dispose" option.
  • Summer.Hooks.initializingEntity: Handles the factories "init" option.
  • Summer.Hooks.applicationContextAware: If implemented on the resolved object, this will call "setApplicationContext" with the context. This hook is registered on the "afterInitialize" phase.
  • Summer.Hooks.contextIdAware: If implement on the resolved object, this will call "setContextId" with the context id. This hook is registered on the "afterInitialize" phase. If implemented with more than one argument, a callback will be supplied as second argument.

Autowired

Autowiring allows a class or initializer to declare its dependencies by id or type.

For example:

class PostService
  Summer.autowire @, collection: 'postCollection'

This will set the property "collection" with the resolved "postCollection" on an instance of "PostService" resolved by Summer.

Another way to declare dependencies is by supplying a type.

For example:

class PostService
  Summer.autowire @, persistenceManager: PersistenceManager

This will look for a factory with a class or subclass of "PersistenceManager". The type must not be ambiguous in the registry, that means there should be only one factory with class/subclass of "PersistenceManager" registered.

How to contribute

If you find what looks like a bug:

Check the GitHub issue tracker to see if anyone else has reported an issue.

If you don’t see anything, create an issue with information about how to reproduce it.

If you want to contribute an enhancement or a fix:

Fork the project on github.

Make your changes with tests.

Commit the changes without making changes to any files that aren’t related to your enhancement or fix.

Send a pull request.

License

Created by Alexander Jentz, Germany.

MIT License. See the included MIT-LICENSE file.

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