Middlewares

Introduction

Middleware functions or middlewares are intermediary functions that sit between the client's request and the server's response. They have access to the request object (req) and the response object (res).

As Manifest works with ExpressJS, Manifest middlewares are ExpressJS middlewares enhanced with the Manifest SDK that allows you to interact with your data with ease.

Middleware use cases

Here are some examples of middleware use cases:

• Patch the request body before storing it in the DB
• Call an external API or any other custom logic
• Hide some data from the response
• Trigger an internal or external action on an event (see also webhooks)

Syntax

manifest/backend.yml

entities:
  Project 🗂️:
    properties:
      - name
      - { name: date, type: date }
    middlewares:
      beforeCreate:
        - handler: setDate
      afterCreate:
        - handler: sendEmail

This example triggers the handler located at /manifest/handlers/setDate.js before the item is created and stored in the database, and triggers /manifest/handlers/sendEmail.js after.

manifest/handlers/setDate.js

module.exports = async (req, res) => {
  console.log('Hello from the handler!')

  req.body['date'] = new Date()
}

tip

You can add several middlewares for an event. They will be processed sequentially in the order you define.

Use your data with the Manifest backend SDK

Manifest passes the JS SDK to handler functions as third argument. You can use it to fetch or write data.

manifest/handlers/patchDocumentNameIfEmpty.js

module.exports = async (req, res, manifest) => {
  // If the 'name' property of the item is empty.
  if (!req.body['name']) {
    // Get the user from the request body.
    const user = await manifest.from('users').findOneById(req.body['userId'])

    // Set a custom name based on the user.
    req.body['name'] = `${user.name}'s untitled document`
  }
}

Events

This is the list and description of the 6 events available to which you can attach middlewares. All of them are related to an entity

Name	Description
beforeCreate	Before creating a record
afterCreate	After creating a record
beforeUpdate	Before updating a record
afterUpdate	After updating a record
beforeDelete	Before deleting a record
afterDelete	After deleting a record