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Usecase Features

Creating a Use Case

usecase(description, body), where:

  • description: use case description, capturing the use case intent.

  • body: object containing the use case structure: request, response, setup, authorize and steps.

  • return: a Herbs use case instance.

Example:

const { Ok, Err, usecase, step, ifElse } = require('@herbsjs/herbs')
const createItem = usecase('Create Item', {
...
})

Good descriptions:

✅ Update User

✅ Reopen Ticket

✅ Request Report Generation

Bad descriptions:

❌ updateUsers

❌ Report Gen

Authorizing and Running

Authorizing

.authorize(user), where:

  • user: string or object containing a user payload.

  • return: true for authorized or false for unauthorized.

Running

.run(request), where:

  • request: object containing the request values.

  • return: a result with an Ok or an Err.

Example:

const usecase = createProduct()

const hasAccess = await usecase.authorize(req.user)
if (!hasAccess) {
...
throw new ForbiddenError()
}

const request = { name: 'The best product' }
const response = await usecase.run(request)

Request

First, a use case must define the request fields and its types. This information is used as metadata for Glues. It is also used to validate request payload before running the use case.

{ request: fields }, where:

  • fields: object containing field names and types.

During the use case execution it is possible to read the request value using ctx.req.

For example:

const updateItem = (injection) =>

usecase('Update Item', {
// Input/Request type validation
request: {
id: Number,
description: String,
isDone: Boolean,
position: Number
}

'Retrieve the previous Item from the repository': step(async (ctx) => {
const req = ctx.req // request values
const ret = await repo.findByID(req.id)
...
}),

As a validation example, when it's executed with an id, that is a string, the above use case return is:

const request = { id: '1' }
const ret = await usecase.run(request)

// ret.err
// { request: [{ id :[{ wrongType: "Number" }] }] }

Response

It is possible to define the response type as well. This information is used as metadata for Glues but it is not validated when running the use case.

{ response: type }, where:

  • type: response type.

A use case will run all the steps sequencially or until one of the steps return a Err. The result of a use case is set by the result of the last step executed.

The result value of a use case is set by ctx.ret. It is possible to set this variable any time at any step.

const createProduct = injection =>
usecase('Create Product', {

request: {
name: String,
...
}

'Check if the Product is valid': step(ctx => {
...
if (!isValid) return Err(errors) // it stops the execution here and return a Err
return Ok() // go to the next step
}),

'Save the Product on the repository': step(async ctx => {
...
ctx.ret = await repo.insert(product) // set the return value
return Ok() // last step and return Ok
}),

Request and Response Types

A field in a request or the response can be basic types from Javascript or entities:

Number: double-precision 64-bit binary format IEEE 754 value

String: a UTF‐16 character sequence

Boolean: true or false

Date: represents a single moment in time in a platform-independent format.

Object: the Object class represents one of JavaScript's data types.

Array: the Array class is a object that is used in the construction of arrays.

Entity: entity object represents an gotu base entity.

For array of a certain type use: [type]. Ex: id: [Number] or items: [Item].

The validation will not validatate for presence, so null and undefined are accepted as valid values.

Setup

Like a constructor, it is the first function to be executed before authorize and steps. Can be used to setup the dependency injection, for instance.

{ setup: ctx => {} }, where:

  • ctx: execution context - internal object visible throughout the use case and steps execution

For example:

const addOrUpdateItem = (injection) =>

usecase('Add or Update an Item on a to-do List', {

// Pre-run setup
setup: ctx => (ctx.di = Object.assign({}, dependency, injection)),
...

Authorize

A function executed before any steps to make sure the user is authorized to run the use case.

{ authorize: async (user) => {} }, where:

  • user: an object containing the user's information - this information will be audited.

  • return: must return Ok for authorized and Err for unauthorized.

For example:

const addOrUpdateItem = (injection) =>

usecase('Add or Update an Item on a to-do List', {

// Authorization with Audit
authorize: async (user) => (user.canAddOrUpdateList ? Ok() : Err()),
...

Context (ctx)

The ctx variable is used to access (read and write) the state of the use case and its steps during its execution.

For more details about context, check step context.

Audit

usecase.auditTrail: Retrieve the audit trail of a use case after its execution.

const request = { name: 'The best product' }
const response = await createProduct.run(request)
console.log(createProduct.auditTrail)

process.env.HERBS_EXCEPTION = "audit": Recommended for production environments - Swallow and audit exceptions thrown during the use case execution. This will swallow the exceptions and return a Err on the step. If process.env.HERBS_EXCEPTION is not equal audit any exceptions thrown during a use case execution will be thrown.

Result sample:

{
// object type
type: 'use case',

// use case description
description: 'Add or Update an Item on a to-do List',

// unique Id for each use case execution
transactionId: '9985fb70-f56d-466a-b466-e200d1d4848c',

// total use case execution time in nanosecods
elapsedTime: 1981800n,

// the same user (object) provided on `usecase.authorize(user)`
user: { name: 'John', id: '923b8b9a', isAdmin: true },

// `usecase.authorize(user)` return
authorized: true,

// use case result
return: {
Ok: { item: { id: 100, name: 'Do not forget this', position: 9 } }
},

// steps
steps: [
{
// object type
type: 'step',

// use ase description
description: 'Check if the Item is valid',

// total step execution time in nanosecods
elapsedTime: 208201n ,

// step result
return: {}
},
...
]
}

Documentation

// TODO