// Register context for a callback, it', // Should register this module as global, default: true, // In case if you need to provide custom value AsyncLocalStorage. constructor (private readonly ac: AsyncContext) {}, intercept (context: ExecutionContext, next: CallHandler): Observable { private readonly asyncContext: AsyncContext, That class contains a method that knows how to return an appropriate options object. We'll then walk through how to use async options providers in that context. 'AppController.getHello -> nextTick -> setTimeout', Consider that if we were to insert a logging statement displaying the return value from the following call: we'd see an object that looks pretty much like this: This should be pretty recognizable, as it would plug right into a standard @Module() decorator to declare module metadata (well, all except for the module property, which is part of the Dynamic module API). Let's figure out how to do that. We could expect a dynamic module to be constructed with the following properties: (Note: because the module is preceded by an @Module() decorator that now lists MassiveService as a provider and exports, it our resulting dynamic module will also have those properties. You might be wondering where that ConfigService injectable comes from. We are looking for an easy way to add the tracing things on top of production-ready application. Let's see. Let's connect a few more dots there and take a quick moment to consider that service. We begin by formalizing some definitions. Maybe a feature that we could register an arbitrary object (or function returning an object) with at run-time, and then have that object passed into a constructor. We're taking inspiration from the concepts learned from Custom providers to build a mor Before starting to read about DI providers, lets know what is Dependency Injection mechanism in Angular used for. We're going to work our way up to that result. That's why we're jumping through hoops to be able to pass in our options provider. We already have an intuition that we need a factory provider, so this seems like the right construct: Let's tie a few things together. [Nest] 141168 - 02/01/2022, 11:33:11 PM LOG [InstanceLoader] AsyncContextModule dependencies initialized +47ms }) So following the documentation, I started by adding the database configuration to the app.module.ts like this: This is dependency injection. . Now, let's ask the following: what mechanism is going to actually call our factory function at run time, take the resulting options object, and make it available to the part of our code that needs it? ) This is the right article for you! MassiveJS provides its entire API to each consumer module (e.g., each feature module) through a db object that has methods like: The primary function of the @nestjsplus/massive package is to make a connection to the database, and return the db object. If you made it this far - congrats! so we develo You cant easily change this in a deployed application, it clutters your app.module.ts file and if you commit this to a public repository, you make your database access data public. If you've played around with any NestJS modules - such as @nestjs/typeorm, @nestjs/passport or @nestjs/jwt - you'll have noticed that they go beyond the features described in that chapter. Since our consumer module (the one calling registerAsync() to import the MassiveJS module) is handing us a class and expecting us to call a method on that class, we can surmise that we'll probably need to use some sort of factory pattern. This is higher order functionality at its best. However, its not that these parameters are data, but rather the same thing type of dependencies youd As mentioned, we're now going to take that concept one step further, and let our options object be provided dynamically at run-time.

First we'll write some glue code to pull this all together. /** I post there as Y Prospect. As we learned in the Dynamic modules chapter, this options object is used to customize the behavior of the module. This is a fairly advanced chapter, and along with some recent significant improvements to the asynchronous providers chapter, Nest developers have some great new resources to help build configurable modules that can be assembled into complex, robust applications. As mentioned, we're now going to take that concept one step further, and let our options object be provided dynamically at run-time. In our feature modules, we then access the database using methods hung off the db object, like those shown above. It needs to return an object of type MassiveConnectOptions (the interface we defined a minute ago). To give us a concrete working example for the remainder of this article, I'm going to introduce a new module. The first provider is obviously the MassiveService itself, which we plan to use in our consumer's feature modules, so we duly export it. Coupled with Nest's signature Dependency Injection features, this is an extremely powerful combination.

'AppController.getHello -> nextTick', This will strongly reinforce the patterns and help you firmly connect all the dots. We're not yet ready to assemble the entire dynamic module. Before we do that, we have to work out the mechanics of our options provider. { this.ac.register() // Important to call .register or .registerCallback (good for middleware) setTimeout(() => { But before the cutting and pasting starts, let's make sure to understand the template so we can customize it to our needs. The patterns illustrated above are used throughout Nest's add-on modules, like @nestjs/jwt, @nestjs/passport and @nestjs/typeorm. useExisting - to re-use an existing (shared. return this.appService.getHello() We just worked out all the mechanics of assembling a dynamically configurable module. } Bear in mind that we are walking through a design pattern that, once you understand it, you can confidently cut-and-paste as boilerplate to start building any module that needs dynamic configuration. This should be a familiar pattern if you're already using some sort of configuration module that implements various functions to return options of a particular shape for each service it gets plugged into. As we learned in the dynamic modules chapter, all that glue should live in the module definition class. Just remember that you won't have to write this from scratch each time! If @Injectable()decorator is added above class with { providedIn: root } object inside it, then it is ad For the sake of registering your services, however, you're going to need to implement (i.e create a class that inherits) ThunderboltRegistration as a partial class in each project where you may want to register services. What is Koin? We've now worked out the concepts and sketched out the piece parts of our dynamically configurable module. The service -- the one that connects and returns a db object -- is, predictably enough, declared in the MassiveService class. Nest fully embraces Node.js Promises and the async/await paradigm. Let's create the MassiveModule class for that purpose. In the dynamic modules chapter, the end result of the code sample is the ability to pass in an options object to configure a module that is being imported. Make sure you have a firm grasp on the concepts in the Custom providers and Dynamic modules chapters before moving on to the next section. In our context, it means we can ensure that we re-use an existing options provider rather than instantiating a new one. If you need a quick refresher course on custom providers, go ahead and re-read the Custom providers chapter now. process.nextTick(() => { * omitted here for brevity AsyncContextModule.forRoot(, 's better to use this method inside the interceptor As a side note, we're using JSDoc to document them so that we get a nice Intellisense developer experience when we later use the module. One other thing that should be obvious from looking at the generated useFactory syntax above is that the ConfigService class must implement a createMassiveConnectOptions() method. Hopefully you now see not only how powerful these patterns are, but how you can make use of them in your own project. [Nest] 141168 - 02/01/2022, 11:33:11 PM LOG [NestApplication] Nest application successfully started +5ms It's important to remember that the 'MASSIVE_CONNECT_OPTIONS' provider is just fulfilling a dependency inside the dynamic module. The important point is how we either instantiate a new ConfigService object, or inject an existing one. This is described in detail here in the Custom providers chapter, but basically, the idea is that the factory function takes optional input arguments which, if specified, are resolved by injecting a provider from the inject property array. We're going to focus now on generalizing and optimizing our registerAsync() method to support the additional techniques described above. This would give us a great deal of flexibility in how we can generate the options dynamically at run-time. The section heading above is quite a mouthful! this.logger.log( This sometimes-overlooked construct is actually extremely useful. Let's get a firm handle on what this code does. export class AsyncContextInterceptor implements NestInterceptor { In this article, we'll further explore why you may need this feature, and how to build it. this.logger.log( * user password, or a function that returns one . Briefly, the package wraps the MassiveJS library into a Nest module. Let's just remind ourselves again how that looks from the consumer perspective: We can refer to this as configuring our dynamic module with a useClass technique (AKA a class provider). Let's dig in to the implementation. After reading that chapter, we know how the following code snippet works via the dynamic module API. And join us at Discord for more happy discussions about NestJS. I'll wait right here. Feel free to ask questions, make comments or suggestions, or just say hello in the comments below. I recently published the @nestjsplus/massive package to enable a Nest project to easily make use of the impressive MassiveJS library to do database work. So we have: Nice!

*/. this.ac.set('traceId', randomUUID()) // Setting default value traceId [Nest] 141168 - 02/01/2022, 11:33:13 PM LOG [7398d3ad-c246-4650-8dd0-f8f29238bdd7] AppController.getHello this.asyncContext.get('traceId') (Collection and Share based on the CC Protocol.). This is going to be a long section, so take a deep breath, maybe refill your coffee cup, but don't worry - we can do this! The useExisting technique is our friend here. In addition to supporting the register() method shown above, they also support a fully dynamic and asynchronous version of the method. So you've noticed the cool ways in which you can dynamically configure some of the out-of-the-box NestJS modules like @nestjs/jwt, @nestjs/passport and @nestjs/typeorm, and want to know how to do that in your own modules? It's worth working through those details, as the concepts will give you a full picture of how NestJS modules and providers fit together in a coherent way. You should be able to trace the path through this code to see how it handles each case uniquely. Hence, we now see the "async" part of our async options provider coming into play. Good so far? Let's say that wasn't true, and that it lives in ConfigModule which has not somehow registered ConfigService as a global provider. Well of course, we've got the awesome NestJS Dependency Injection system at our disposal. That's it. How about instead I give you a class that has a method you can call to get the option values?". We can model our registerAsync() interface based on those patterns. So you know how I mentioned earlier that dependency injection is a software design pattern, well, thats not entirely true. * use SSL (it also can be a TSSLConfig-like object) The recipe for binding something to the Nest IoC container, and later having it injected, is captured in an object called a provider. To answer that, first consider once again that our example above (the ConfigModule.register({ folder: './config'}) part) is passing a static options object in to the register() method. Now perhaps you can see a little more clearly how this all fits together. }, 0) }, [Nest] 141168 - 02/01/2022, 11:33:11 PM LOG [NestFactory] Starting Nest application The rest of the article is gravy! In other words, somewhere, we're going to have to instantiate that class, call a method on it, and use the result returned from that method call as our connection options, right? I highly recommend you do the following exercise. Consider another question. */, Using ArcPy.TableToExcel_conversion in Script Tool removes automatically added data, We're writing code that constructs, then returns, a dynamic module (our, The dynamic module it returns can be imported into other feature modules, and provides a service (the thing that connects to the database and returns a. [Nest] 141168 - 02/01/2022, 11:33:13 PM LOG [7398d3ad-c246-4650-8dd0-f8f29238bdd7] AppController.getHello -> nextTick -> setTimeout, You need to replace AsyncHooksModule by AsyncContextModule.forRoot(), Openbase is the leading platform for developers to discover and choose open-source. What is dependency and dependency Injection? Finally, we have a third provider, also used only internally by our dynamic module (and hence not exported), which is our single private instance of the ConfigService. What the heck is an async options provider? Once made, it caches the connection so it can return an existing connection on subsequent calls. To access Once my team have to track the application behavior after it had been deployed to production for a few months. Nest makes it super easy to support either. This is really where the rubber meets the road, so take time to understand it carefully. As a final bonus, if you're building an Open Source package for public use, just combine this technique with the steps described in my last article , and you're all set. Dependency Injection is a software design pattern. What would useFactory look like when exposed as an option for our registerAsync() method? Basically, we're saying "Hey module! We'll study the architecture of that package and use parts of it for the code we analyze in this article. useFactory - to use a function as the options provider. You may recall seeing several other similar patterns in the Custom providers chapter. (Review that chapter before proceeding if this concept is not familiar).

export class AppController { Now you can confidently start using these powerful patterns in your own code to create robust and flexible modules that work reliably in a wide variety of contexts.

That was the hardest part. [Nest] 141168 - 02/01/2022, 11:33:13 PM LOG [7398d3ad-c246-4650-8dd0-f8f29238bdd7] AppController.getHello -> nextTick But this article is already too long, so I'll leave that as an exercise for you, dear reader. ) {}, @Get() For example, useClass: ConfigService will cause Nest to create and inject a new private instance of our ConfigService. [Nest] 141168 - 02/01/2022, 11:33:11 PM LOG [RouterExplorer] Mapped {/, GET} route +7ms Above we are just showing the elements that get added dynamically.). The similarities are deliberate. We're trying to supply MassiveJS with its expected connection options, so first we'll create an interface to model that: There are actually more options available (we can see what they are from examining the MassiveJS connection options documentation), but let's keep the choices basic for now. You can also see a slightly evolved version of the code in this article in the @nestjsplus/massive repository (while you're there, maybe give it a quick if you like this article ). We'll describe what's happening in this code just below it. And that's exactly what we can do with Nest's @nestjs/jwt module as shown in the example above. Right off the bat, it should be clear that in order to establish a database connection, we need to pass in some connection parameters. Now let's figure out how to do that in our Massive module. The next concept to grapple with is as follows. Openbase helps you choose packages with reviews, metrics & categories. The main difference between the code in this article and that repo is that the production version needs to handle multiple asynchronous options providers, so there's a tiny bit more plumbing. Our registration would instead look like this: And our resulting dynamic module would look like this: Another exercise is to ponder the difference in the code paths when you use useClass vs. useExisting. Well - heh heh - that's kind of a trick question.

register(): void Let's sketch out what those techniques would look like from a consumer module perspective, and then we can easily add support for them. In the real world, we'll usually want a single shared instance of the ConfigService injected anywhere it's needed, not a private copy. I'll describe the key elements below. * public static register( ) This implies that our dynamic module is going to need to do a little more work in this case, as compared to the static options technique, to acquire its connection options. private readonly logger: Logger That seems like a good fit!

Can our code handle this? imports: [ Now that I mention it, we haven't really looked at the service that depends on the 'MASSIVE_CONNECT_OPTIONS' provider we're working so hard to supply. Are there other techniques? Zero-dependency module for NestJS that allow to track context between async call, The first step is to register AsyncContext inside interceptor (or middleware), @Injectable() When we're done, our module will support all three techniques: I'm going to jump right to the code, as we're all getting weary now . We're going to construct that configuration options object at run-time, using a class that the consuming module hands us. Sounds (kind of) like a factory. How is the ConfigService available inside the factory for injection in this useExisting case? One of the hallmarks of NestJS is making asynchronous programming very straightforward. this.logger.log('AppController.getHello', this.asyncContext.get('traceId')) This article builds on that foundation and takes it one step further. // <-- we need to get our options factory inserted here! That, in a nutshell, is the purpose of async options providers.

So instead of reading the next few paragraphs in the database part of the , I started to search for options o This website uses cookies to ensure you get the best experience on our website. We're in pretty deep, so now's a good time to do a quick refresher on the big picture, and assess where we're at: OK, so we're working on steps 4, 5, and 6 right now. What we've built so far allows us to configure the MassiveModule by handing it a class whose purpose is to dynamically provide connection options. Here's how it would look: We're in the home stretch. OK, so now you remember that we can define our options provider with a construct like the following. [Nest] 141168 - 02/01/2022, 11:33:11 PM LOG [RoutesResolver] AppController {/}: +12ms To begin with, we can imagine supporting a module import statement using the same construct we found in @nestjs/jwt, like this: If this doesn't look familiar, take a quick look at this section of the Custom providers chapter. useClass - to get a private instance of the options provider. In our case, with PostgreSQL, those parameters would be something like: What we quickly realize is that it's not optimal to hard-code those connection parameters in our Nest app. return next.handle()

/** We'll sketch a static version of the object, just to see what we're trying to generate dynamically in the code we're about to write: So we've now figured out what our generated options provider should look like. Over on the NestJS documentation site, we recently added a new chapter on dynamic modules. [Nest] 141168 - 02/01/2022, 11:33:11 PM LOG [InstanceLoader] AppModule dependencies initialized +1ms It's surprisingly straightforward: The MassiveService class injects the connection options provider and uses that information to make the API call needed to asynchronously create a database connection (await massive(this._massiveConnectOptions)). constructor ( We told our module to useClass, which means "create your own instance"), and that will be injected into the factory. FOCUS ON FINDING GREAT DEVELOPER CONTENT We're going to use the NestJS Dependency Injection system to do the heavy lifting to manage that options object dependency for us. So, Nest is going to instantiate a ConfigService inside the dynamic module context (this makes sense, right? The ones we modelled are required to establish a connection. Let's look at how these features can be used to create dynamically configurable modules. We have a relation between Car and Engine classes. Hmmm if only we had some general purpose mechanism. . Construct an arbitrary registerAsync() registration call on paper, and walk through the code to predict what the returned dynamic module will look like. Compare that to hardcoding a parameter, as with ConfigModule.register({ folder: './config'}), and you can immediately see the win. We can fill in those values based on how the registerAsync() call was made: Let's go ahead and fill them in now based on what we know. I don't want to give you the option property values in code. Let's take a little closer look at that useFactory construct. Dependency Injection is a technique to make the classes in Object Oriented Programming easier to test and configure. Let's whip up an options provider that will meet our needs.

. Configuration options are provided based on values extracted from the environment by the ConfigService, meaning they can be changed completely external to your feature code. If you have questions, feel free to ask in the comments below! ) Anybody got any ideas? Mastering this skill lets you build modules that are re-usable in any context. private readonly appService: AppService, To describe it in English, we're returning a dynamic module that declares three providers, exporting one of them for use in other modules that may import it. this.asyncContext.get('traceId')

*/, /** We can return the options object directly, or return a Promise that will resolve to an options object. Before discussing the details of the code, let's cover a few superficial changes to make sure they don't trip you up. While we did make use of a factory in the previous section, that was strictly internal to the dynamic module construction mechanics, not a part of the callable API. For example, with the @nestjs/jwt module, you can use a construct like this: With this construct, not only is the module dynamically configured, but the options passed to the dynamic module are themselves constructed dynamically. } getHello (): string { The method could be something like createMassiveConnectOptions(). It won't take long. As a next step, you may want to consider browsing through the source code of those modules, now that you have a roadmap. // <-- we need to supply injectable parameters for useFactory here! The second provider ('MASSIVE_CONNECT_OPTIONS') is only used internally by the MassiveService to ingest the connection options it needs (notice that we do not export it). Let's go with that concept for now. A pragmatic lightweight dependency injection framework for Kotlin developers Written in pure Kotlin. This enables fully context-aware, re-usable packages (libraries), and lets you assemble apps that deploy smoothly across cloud providers and throughout the DevOps spectrum - from development to staging to production. Returning to that task, we should be able to see how to fill in the blanks in the skeleton options provider we sketched out earlier (see the lines annotated <-- we need to above). Read on . First, let's revisit what we expect to accomplish with the registerAsync() construct above. We're ready to start assembling them. Let's describe our prospective factory with an interface. In the sample above, I assumed that it was already visible inside the consuming module -- perhaps as a global module (one declared with @Global()).

In the sample above, we supplied a very simple factory in place, but we could of course plug in (or pass in a function implementing) any arbitrarily sophisticated factory as long as it returns an appropriate connections object. }, The last step is to inject AsyncContext inside controller or service and use it, @Controller() Note that there's also an inject property, which is used to inject the ConfigService into the factory function. The conventional solution is to supply them through some sort of Configuration Module. We're taking inspiration from the concepts learned from Custom providers to build a more flexible means of supplying options to our dynamic modules.