Asked  7 Months ago    Answers:  5   Viewed   49 times

I hear people talking about dependency injection and the benefit of it all the time, but I don't really understand it.

I'm wondering if it's a solution to the "I pass database connections as arguments all the time" problem.

I tried reading wikipedia's entry on it, but the example is written in Java so I don't solidly understand the difference it is trying to make clear. ( http://en.wikipedia.org/wiki/Dependency_injection ).

I read this dependency-injection-in-php article ( http://www.potstuck.com/2009/01/08/php-dependency-injection/ ), and it seems like the objective is to not pass dependencies to an object directly, but to cordon off the creation of an object along with the creation of it's dependencies. I'm not sure how to apply that in a using php functions context, though.

Additionally, is the following Dependency Injection, and should I bother trying to do dependency injection in a functional context?

Version 1: (the kind of code that I create, but don't like, every day)

function get_data_from_database($database_connection){
    $data = $database_connection->query('blah');
    return $data;
}

Version 2: (don't have to pass a database connection, but perhaps not dependency injection?)

function get_database_connection(){
    static $db_connection;
    if($db_connection){
        return $db_connection;
    } else {
        // create db_connection
      ...
    }
}

function get_data_from_database(){
   $conn = get_database_connection();
   $data = $conn->query('blah');
   return $data;
}

$data = get_data_from_database();

Version 3: (the creation of the "object"/data is separate, and the database code is still, so perhaps this would count as dependency injection?)

function factory_of_data_set(){
    static $db_connection;
    $data_set = null;
    $db_connection = get_database_connection();
    $data_set = $db_connection->query('blah');
    return $data_set;
}

$data = factory_of_data_set();

Anyone have a good resource or just insight that makes the method and benefit -crystal- clear?

 Answers

10

Dependency injection is a big word for "I have some more parameters in my constructor".

It's what you did before the awfull Singleton wave when you did not like globals :

<?php
class User {
    private $_db;
    function __construct($db) {
        $this->_db = $db;
    }
}

$db   = new Db();
$user = new User($db);

Now, the trick is to use a single class to manage your dependencies, something like that :

class DependencyContainer 
{
    private _instances = array();
    private _params = array();

    public function __construct($params)
    {
        $this->_params = $params;
    }

    public function getDb()
    {
        if (empty($this->_instances['db']) 
            || !is_a($this->_instances['db'], 'PDO')
        ) {
            $this->_instances['db'] = new PDO(
                $this->_params['dsn'],
                $this->_params['dbUser'], 
                $this->_params['dbPwd']
            );
        }
        return $this->_instances['db'];
    }
}

class User
{
    private $_db;
    public function __construct(DependencyContainer $di)
    {
         $this->_db = $di->getDb();
    }
}

$dependencies = new DependencyContainer($someParams);
$user = new User($dependencies);

You must think you just another class and more complexity. But, your user class may need something to log messages like lot of other classes. Just add a getMessageHandler function to your dependency container, and some $this->_messages = $di->getMessageHandler() to your user class. Nothing to change in the rest of your code.

You'll get lot of infos on symfony's doc

Wednesday, March 31, 2021
 
Ula
answered 7 Months ago
Ula
76

Recommended Approach

This answer enumerates different mechanisms for passing parameters to FXML controllers.

For small applications I highly recommend passing parameters directly from the caller to the controller - it's simple, straightforward and requires no extra frameworks.

For larger, more complicated applications, it would be worthwhile investigating if you want to use Dependency Injection or Event Bus mechanisms within your application.

Passing Parameters Directly From the Caller to the Controller

Pass custom data to an FXML controller by retrieving the controller from the FXML loader instance and calling a method on the controller to initialize it with the required data values.

Something like the following code:

public Stage showCustomerDialog(Customer customer) {
  FXMLLoader loader = new FXMLLoader(
    getClass().getResource(
      "customerDialog.fxml"
    )
  );

  Stage stage = new Stage(StageStyle.DECORATED);
  stage.setScene(
    new Scene(loader.load())
  );

  CustomerDialogController controller = loader.getController();
  controller.initData(customer);

  stage.show();

  return stage;
}

...

class CustomerDialogController {
  @FXML private Label customerName;
  void initialize() {}
  void initData(Customer customer) {
    customerName.setText(customer.getName());
  }
}

A new FXMLLoader is constructed as shown in the sample code i.e. new FXMLLoader(location). The location is a URL and you can generate such a URL from an FXML resource by:

new FXMLLoader(getClass().getResource("sample.fxml"));

Be careful NOT to use a static load function on the FXMLLoader, or you will not be able to get your controller from your loader instance.

FXMLLoader instances themselves never know anything about domain objects. You do not directly pass application specific domain objects into the FXMLLoader constructor, instead you:

  1. Construct an FXMLLoader based upon fxml markup at a specified location
  2. Get a controller from the FXMLLoader instance.
  3. Invoke methods on the retrieved controller to provide the controller with references to the domain objects.

This blog (by another writer) provides an alternate, but similar, example.

Setting a Controller on the FXMLLoader

CustomerDialogController dialogController = 
    new CustomerDialogController(param1, param2);

FXMLLoader loader = new FXMLLoader(
    getClass().getResource(
        "customerDialog.fxml"
    )
);
loader.setController(dialogController);

Pane mainPane = loader.load();

You can construct a new controller in code, passing any parameters you want from your caller into the controller constructor. Once you have constructed a controller, you can set it on an FXMLLoader instance before you invoke the load() instance method.

To set a controller on a loader (in JavaFX 2.x) you CANNOT also define a fx:controller attribute in your fxml file.

Due to the limitation on the fx:controller definition in FXML, I personally prefer getting the controller from the FXMLLoader rather than setting the controller into the FXMLLoader.

Having the Controller Retrieve Parameters from an External Static Method

This method is exemplified by Sergey's answer to Javafx 2.0 How-to Application.getParameters() in a Controller.java file.

Use Dependency Injection

FXMLLoader supports dependency injection systems like Guice, Spring or Java EE CDI by allowing you to set a custom controller factory on the FXMLLoader. This provides a callback that you can use to create the controller instance with dependent values injected by the respective dependency injection system.

An example of JavaFX application and controller dependency injection with Spring is provided in the answer to:

  • Adding Spring Dependency Injection in JavaFX (JPA Repo, Service)

A really nice, clean dependency injection approach is exemplified by the afterburner.fx framework with a sample air-hacks application that uses it. afterburner.fx relies on JEE6 javax.inject to perform the dependency injection.

Use an Event Bus

Greg Brown, the original FXML specification creator and implementor, often suggests considering use of an event bus, such as the Guava EventBus, for communication between FXML instantiated controllers and other application logic.

The EventBus is a simple but powerful publish/subscribe API with annotations that allows POJOs to communicate with each other anywhere in a JVM without having to refer to each other.

Follow-up Q&A

on first method, why do you return Stage? The method can be void as well because you already giving the command show(); just before return stage;. How do you plan usage by returning the Stage

It is a functional solution to a problem. A stage is returned from the showCustomerDialog function so that a reference to it can be stored by an external class which may wish to do something, such as hide the stage based on a button click in the main window, at a later time. An alternate, object-oriented solution could encapsulate the functionality and stage reference inside a CustomerDialog object or have a CustomerDialog extend Stage. A full example for an object-oriented interface to a custom dialog encapsulating FXML, controller and model data is beyond the scope of this answer, but may make a worthwhile blog post for anybody inclined to create one.


Additional information supplied by StackOverflow user named @dzim

Example for Spring Boot Dependency Injection

The question of how to do it "The Spring Boot Way", there was a discussion about JavaFX 2, which I anserwered in the attached permalink. The approach is still valid and tested in March 2016, on Spring Boot v1.3.3.RELEASE: https://stackoverflow.com/a/36310391/1281217


Sometimes, you might want to pass results back to the caller, in which case you can check out the answer to the related question:

  • JavaFX FXML Parameter passing from Controller A to B and back
Tuesday, June 1, 2021
 
fillobotto
answered 5 Months ago
72

Yes! Although the Azure Functions portal does not currently provide a mechanism to add and manage NuGet packages, the runtime supports NuGet references and will make sure they are correctly used when compiling and executing your functions.

In order to define your dependencies, you need to create a Project.json file with the required NuGet package references. Here is an example that adds a reference to Microsoft.ProjectOxford.Face version 1.1.0:

{
  "frameworks": {
    "net46":{
      "dependencies": {
        "Microsoft.ProjectOxford.Face": "1.1.0"
      }
    }
   }
}

The Azure Functions portal provides a convenient way to manage your function files, which we can use to create (or upload) our project.json:

  1. In the function's develop section, click on view files
  2. Click on the option to create a file (you can also click on the option to upload a file if you have a previously created project.json file on your machine
  3. Name the file project.json and define your package references (you can use the example above as a template).

The package restore process will begin and you should see output similar to the following in your log window:

2016-04-04T19:02:48.745 Restoring packages.
2016-04-04T19:02:48.745 Starting NuGet restore
2016-04-04T19:02:50.183 MSBuild auto-detection: using msbuild version '14.0' from 'D:Program Files (x86)MSBuild14.0bin'.
2016-04-04T19:02:50.261 Feeds used:
2016-04-04T19:02:50.261 C:DWASFilesSitesfacavalfunctestLocalAppDataNuGetCache
2016-04-04T19:02:50.261 https://api.nuget.org/v3/index.json
2016-04-04T19:02:50.261 
2016-04-04T19:02:50.511 Restoring packages for D:homesitewwwrootHttpTriggerCSharp1Project.json...
2016-04-04T19:02:52.800 Installing Newtonsoft.Json 6.0.8.
2016-04-04T19:02:52.800 Installing Microsoft.ProjectOxford.Face 1.1.0.
2016-04-04T19:02:57.095 All packages are compatible with .NETFramework,Version=v4.6.
2016-04-04T19:02:57.189 
2016-04-04T19:02:57.189 
2016-04-04T19:02:57.455 Packages restored.

As expected, the Azure Functions runtime will automatically add the references to the package assemblies, so you DO NOT need to explicitly add assembly references using #r "AssemblyName", you can just add the required using statements to your function and use the types defined in the NuGet package you've referenced.

Additional deployment options

Since Azure Functions is built on top of App Services, as an alternative to the steps above, you also have access to all the great deployment options available to standard Azure Web Apps (Azure Websites).

Here are some examples:

Using App Service Editor (Monaco)

In order to manage your files directly from your browser by using the App Service Editor (Monaco):

  • On the Azure Functions portal, click on Function app settings
  • Under the Advanced Settings section, click on Go to App Service Settings
  • Click on the Tools button
  • Under Develop, click on App Service Editor
  • Turn it On if it is not already enabled and click on Go
  • Once it loads, drag-and-drop your project.json file into your function's folder (the folder named after your function.

Using SCM (Kudu) endpoint

  • Navigate to: https://<function_app_name>.scm.azurewebsites.net
  • Click on Debug Console > CMD
  • Navigate to D:homesitewwwroot<function_name>
  • Drag-and-drop your Project.json file into the folder (onto the file grid)

FTP

  • Follow the instructions here to get FTP configured
  • Once connected (following the instructions above) copy your Project.json file to /site/wwwroot/<function_name>

    For additional deployment options, see: https://azure.microsoft.com/en-us/documentation/articles/web-sites-deploy/

Continuous Integration

If you enable continuous integration and deploy your function with a project.json file when your Function App is not running, the package restore will happen automatically once your Function App initializes. It is recommended that you do not add your project.lock.json file to source control.

Pre-compiled assemblies

Functions may also be deployed as pre-compiled assemblies, and in this case, all dependency management is handled in Visual Studio. This option may be used as standard class libraries on any version of Visual Studio or by using the Visual Studio 2017 Azure Functions Tools.

Tuesday, June 1, 2021
 
tplaner
answered 5 Months ago
77

If you have several dependencies to deal with, then yes a DI container can be the solution.

The DI container can be an object or array constructed of the various dependent object you need, which gets passed to the constructor and unpacked.

Suppose you needed a config object, a database connection, and a client info object passed to each of your classes. You can create an array which holds them:

// Assume each is created or accessed as a singleton, however needed...
// This may be created globally at the top of your script, and passed into each newly
// instantiated class
$di_container = array(
  'config' = new Config(),
  'db' = new DB($user, $pass, $db, $whatever),
  'client' = new ClientInfo($clientid)
);

And your class constructors accept the DI container as a parameter:

class SomeClass {
  private $config;
  private $db;
  private $client;
 
  public function __construct(&$di_container) {
    $this->config = $di_container['config'];
    $this->db = $di_container['db'];
    $this->client = $di_container['client'];
  }
}

Instead of an array as I did above (which is simple), you might also create the DI container as an class itself and instantiate it with the component classes injected into it individually. One benefit to using an object instead of an array is that by default it will be passed by reference into the classes using it, while an array is passed by value (though objects inside the array are still references).

Edit

There are some ways in which an object is more flexible than an array, although more complicated to code initially.

The container object may also create/instantiate the contained classes in its constructor as well (rather than creating them outside and passing them in). This can save you some coding on each script that uses it, as you only need to instantiate one object (which itself instantiates several others).

Class DIContainer {
  public $config;
  public $db;
  public $client;

  // The DI container can build its own member objects
  public function __construct($params....) {
    $this->config = new Config();

    // These vars might be passed in the constructor, or could be constants, or something else
    $this->db = new DB($user, $pass, $db, $whatever);

    // Same here -  the var may come from the constructor, $_SESSION, or somewhere else
    $this->client = new ClientInfo($clientid);
  }
}
Wednesday, June 23, 2021
 
JohnnyW
answered 4 Months ago
12

Instead of resolving at construction, ActionExecutingContext.HttpContext.RequestServices should give you a reference to the request's service container at the time of the request.

So:

public override void OnActionExecuting(ActionExecutingContext filterContext)
{
    var svc = filterContext.HttpContext.RequestServices;
    var memCache = svc.GetService<IMemoryCache>();
    //..etc
Thursday, July 1, 2021
 
Kenny
answered 4 Months ago
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