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docs: cover useexisting variant for configurable module cls
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‎content/fundamentals/dynamic-modules.md

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@@ -343,6 +343,45 @@ Extending the `ConfigurableModuleClass` means that `ConfigModule` provides now n
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export class AppModule {}
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```
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The `registerAsync` method takes the following object as an argument:
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```typescript
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{
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/**
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* Injection token resolving to a class that will be instantiated as a provider.
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* The class must implement the corresponding interface.
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*/
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useClass?: Type<
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ConfigurableModuleOptionsFactory<ModuleOptions, FactoryClassMethodKey>
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>;
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/**
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* Function returning options (or a Promise resolving to options) to configure the
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* module.
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*/
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useFactory?: (...args: any[]) => Promise<ModuleOptions> | ModuleOptions;
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/**
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* Dependencies that a Factory may inject.
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*/
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inject?: FactoryProvider['inject'];
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/**
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* Injection token resolving to an existing provider. The provider must implement
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* the corresponding interface.
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*/
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useExisting?: Type<
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ConfigurableModuleOptionsFactory<ModuleOptions, FactoryClassMethodKey>
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>;
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}
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```
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Let's go through the above properties one by one:
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- `useFactory` - a function that returns the configuration object. It can be either synchronous or asynchronous. To inject dependencies into the factory function, use the `inject` property. We used this variant in the example above.
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- `inject` - an array of dependencies that will be injected into the factory function. The order of the dependencies must match the order of the parameters in the factory function.
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- `useClass` - a class that will be instantiated as a provider. The class must implement the corresponding interface. Typically, this is a class that provides a `create()` method that returns the configuration object. Read more about this in the [Custom method key](/fundamentals/dynamic-modules#custom-method-key) section below.
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- `useExisting` - a variant of `useClass` that allows you to use an existing provider instead of instructing Nest to create a new instance of the class. This is useful when you want to use a provider that is already registered in the module. Keep in mind that the class must implement the same interface as the one used in `useClass` (and so it must provide the `create()` method, unless you override the default method name, see [Custom method key](/fundamentals/dynamic-modules#custom-method-key) section below).
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Always choose one of the above options (`useFactory`, `useClass`, or `useExisting`), as they are mutually exclusive.
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Lastly, let's update the `ConfigService` class to inject the generated module options' provider instead of the `'CONFIG_OPTIONS'` that we used so far.
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```typescript
@@ -431,17 +470,18 @@ There are edge-cases when your module may need to take extra options that determ
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In such cases, the `ConfigurableModuleBuilder#setExtras` method can be used. See the following example:
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```typescript
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export const { ConfigurableModuleClass, MODULE_OPTIONS_TOKEN } = new ConfigurableModuleBuilder<ConfigModuleOptions>()
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.setExtras(
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{
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isGlobal: true,
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},
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(definition, extras) => ({
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...definition,
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global: extras.isGlobal,
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}),
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)
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.build();
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export const { ConfigurableModuleClass, MODULE_OPTIONS_TOKEN } =
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new ConfigurableModuleBuilder<ConfigModuleOptions>()
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.setExtras(
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{
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isGlobal: true,
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},
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(definition, extras) => ({
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...definition,
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global: extras.isGlobal,
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}),
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)
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.build();
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```
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In the example above, the first argument passed into the `setExtras` method is an object containing default values for the "extra" properties. The second argument is a function that takes an auto-generated module definitions (with `provider`, `exports`, etc.) and `extras` object which represents extra properties (either specified by the consumer or defaults). The returned value of this function is a modified module definition. In this specific example, we're taking the `extras.isGlobal` property and assigning it to the `global` property of the module definition (which in turn determines whether a module is global or not, read more [here](/modules#dynamic-modules)).
@@ -465,7 +505,9 @@ However, since `isGlobal` is declared as an "extra" property, it won't be availa
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```typescript
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@Injectable()
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export class ConfigService {
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constructor(@Inject(MODULE_OPTIONS_TOKEN) private options: ConfigModuleOptions) {
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constructor(
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@Inject(MODULE_OPTIONS_TOKEN) private options: ConfigModuleOptions,
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) {
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// "options" object will not have the "isGlobal" property
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// ...
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}
@@ -479,7 +521,11 @@ The auto-generated static methods (`register`, `registerAsync`, etc.) can be ext
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```typescript
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import { Module } from '@nestjs/common';
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import { ConfigService } from './config.service';
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import { ConfigurableModuleClass, ASYNC_OPTIONS_TYPE, OPTIONS_TYPE } from './config.module-definition';
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import {
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ConfigurableModuleClass,
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ASYNC_OPTIONS_TYPE,
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OPTIONS_TYPE,
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} from './config.module-definition';
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@Module({
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providers: [ConfigService],
@@ -505,5 +551,10 @@ export class ConfigModule extends ConfigurableModuleClass {
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Note the use of `OPTIONS_TYPE` and `ASYNC_OPTIONS_TYPE` types that must be exported from the module definition file:
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```typescript
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export const { ConfigurableModuleClass, MODULE_OPTIONS_TOKEN, OPTIONS_TYPE, ASYNC_OPTIONS_TYPE } = new ConfigurableModuleBuilder<ConfigModuleOptions>().build();
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export const {
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ConfigurableModuleClass,
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MODULE_OPTIONS_TOKEN,
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OPTIONS_TYPE,
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ASYNC_OPTIONS_TYPE,
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} = new ConfigurableModuleBuilder<ConfigModuleOptions>().build();
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```

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