Dependency Injection and Nashorn

[Luis Rodrigues]

Hi all,

With the previous global method using :

import play.db.DB;

DB.getConnection();

we could write a class that should be easily injected inside NashHorn and used by the server side javascript and accessible 

simply with something like this:

var DbFoo = Java.type('com.foo.bar.CreatedDBClass');
var db = new DbFoo();
var result = db.query("sql query");

But changing to play 2.6 with Dependency Injection, that will be a lot harder because we don't have a way to call the class with the required 

Database class from the javascript side.

Do you have any plan to workaround this ? or any suggestion ?

Thanks

-Luis

[Luis Rodrigues]

Currently I have a small workaround for this that is not super elegant and required creating objects to wrap the java classes in the javascript side, that inject the parameter [Database]  automatically in the java class and with this we are avoiding the user to set the parameter all the time (annoying) and to send the Database /Connection class to the javascript engine every time that we receive a request in the controller.

So,

I created a JSEngine service because we need to use hot executions and use the same engine all the time to use already "compiled" code ... :

@Singleton
public class JavascriptEngine implements JSEngine {
    private Database db;
    ScriptEngineManager factory;
    ScriptEngine engine;

    @Inject
    public JavascriptEngine(Database db) {
        this.db = db;
     ....

and 

Basically I'm setting a special variable inside the javascript engine every time that I receive a request in the controller and sending the Database object
to the javascript side/engine: (not perfect)

public class  ControllerA extends Controller {

     @Inject
     JavascriptEngine jsengine;
....

     jsengine.addToEngine(db); // this basically calls the method (engine.put("DS_DATABASE",db);)

works fine, but I want to know if you have a better approach for this or any suggestion ?

Thanks

Regards

-Luis

[Will Sargent]

You can dependency inject the database instance directly, or (if you are really hard up and want the user to have unbounded visibility) you can inject the Injector itself -- at the point that you're calling "com.foo.bar.CreatedDBClass" you're delegating the lookups there anyway.  

The big problem is that doing database queries from Javascript inside of Play will pretty much require you do everything inside one big custom thread pool there, because you can't control the blocking operations inside that Javascript engine (or at least multi-threading was not a thing there the last time I looked).

--

Will Sargent

Engineer, Lightbend, Inc.

will.s...@lightbend.com

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[David Heidrich]

Hey,

maybe the plugin I wrote to execute Javascript for play could be of help:

https://github.com/BowlingX/play-webpack

It also supports promises and async execution (it uses akka underneath)

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[Will Sargent]

Hi David,

This looks really interesting -- do you have a blog post or documentation on this?

--

Will Sargent

Engineer, Lightbend, Inc.

will.s...@lightbend.com

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[David Heidrich]

Hi Sargent,

not yet, I have a sample application but it's a private repo. I will create an example this week.

--

David

[David Heidrich]

Hi,

I created an example/boilerplate Project:

https://github.com/BowlingX/play-webpack-example

--

David

Am Dienstag, 13. Juni 2017 02:43:24 UTC+2 schrieb Will Sargent: