archived-sern-website/docs/guide/walkthrough/services.md

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Services

:::tip This is version 3 api only!! :::

:::tip TLDR: The direct upgrade to useContainer. if you set up a bot with create-bot, check dependencies.d.ts. Dependencies are the types that Services uses. :::

You need someway to use dependencies in your command module. Services to the rescue!

import { CoreDependencies, Singleton } from '@sern/handler'
import { Client } from 'discord.js'

interface Dependencies extends CoreDependencies { 
    '@sern/client': Singleton<Client>
}

Recall, some keys in Dependencies are special.

Special key dependency must implement its contracts.

• @sern/client: Your discord client. -> Emitter
• @sern/logger: Log data -> Logging
• @sern/errors: Handling errors and lifetime -> ErrorHandling
• @sern/modules: Managing all command modules -> ModuleManager
• @sern/emitter: is the key to emit events and occurences in a project -> Emitter

Lets try to access the client you provided.

import { Service } from '@sern/handler'

export default commandModule({ 
   // ...
    execute: (ctx) => {
        //Client!
        const client = Service('@sern/client');
    }
   // 
})

import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem';

Safety

• Services cannot be called in other services while makeDependencies is forming.

Lets pass a logger into our database.

await makeDependencies({ 
    build: root => root
        //Overriding the default logger provided.
        .upsert({ '@sern/logger': single(() => new Logger()) })

        // Wiring our logger into the database.
        .add(ctx =>  {
            return { database: single(() => new Database(ctx['sern/logger']))) }
        })
})

await makeDependencies({ 
    build: root => root
        //Overriding the default logger provided.
        .upsert({ '@sern/logger': single(() => new Logger()) })

        // Wiring our logger into the database.
        // We wire our database incorrectly. Logger should be passed INTO the constructor
        .add({ database: single(() => new Database()) })
})

import { Service, makeDependencies } from '@sern/handler';

//Calling Service prematurely!
const logger = Service('@sern/logger');

class Database {
    
    constructor() {
        this.logger = logger
    }
}

This is a code smell anyway. It breaks encapsulation and defeats the purpose of wiring dependencies

• Services can only be used after sern has made dependencies.

  • Calling a service before will crash your application.

• Services can be safely used outside of commandModules.

  • Be careful to not cause too many side effects.

• You will need to wire dependencies together.

await makeDependencies(...pass your options here)

// This is guaranteed to be defined if configured correctly
import { Service } from '@sern/handler';
const client = Service('@sern/client');

import { Service, makeDependencies } from '@sern/handler';
/* DON'T USE SERVICES BEFORE CALLING makeDependencies */
const logger = Service('@sern/logger');

await makeDependencies()

• Services can only be used after sern has made dependencies.
  • Calling a service before will crash your application.
• Services can be safely used outside of commandModules.
  • Be careful to not cause too many side effects.

Related api

• use Service for single dependency.
• use Services for multiple dependencies.