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How to add your own business logic in a LoopBack app.
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README.md

loopback-example-app-logic

$ git clone https://github.com/strongloop/loopback-example-app-logic.git
$ cd loopback-example-app-logic
$ npm install
$ node .
# then in a different tab, run ./bin/remote-method-request or ./bin/datetime-request

In this example, we demonstrate remote methods, remote hooks, model operation hooks, boot scripts, middleware, and email-connector as solutions for integrating user-defined logic into a LoopBack application.

Prerequisites

Tutorials:

Knowledge:

Procedure

Create the application

Application information:

  • Name: loopback-example-app-logic
  • Directory to contain the project: loopback-example-app-logic
$ lb app loopback-example-app-logic
... # follow the prompts
$ cd loopback-example-app-logic

Add a model

Model information:

  • Name: car
    • Datasource: db (memory)
    • Base class: PersistedModel
    • Expose via REST: Yes
    • Custom plural form: Leave blank
    • Properties
      • make
        • String
        • Not required
      • model
        • String
        • Not required
$ lb model car
... # follow the prompts

Define a remote method

Define a remote method in car.js.

The remote method takes a "sound" and repeats it three times.

Test it by starting the server (using node .) and running curl -XPOST localhost:3000/api/cars/rev-engine -H 'content-type:application/json' -d '{"sound":"vroom"}'.

If you are using Windows, single quotes are treated as backticks in cmd. This means you will have to modify the curl command to use and escape double quotes instead: curl -XPOST localhost:3000/api/cars/rev-engine -H "content-type:application/json" -d "{\"sound\":\"vroom\"}".

You should see:

...
{"engineSound":"vroom vroom vroom"}

Define a remote method before hook

Define a remote method before hook in car.js.

The second parameter unused must be provided for legacy reasons. You may simply ignore it, but you must declare it to ensure next is the third parameter. This is a side effect of inheriting from the jugglingdb library.

context contains the Express request and response objects (ie. context.req and context.res).

This method is triggered right before revEngine is called and prints a message to the console.

Restart the server.

$ ./bin/remote-method-request

You should see:

...
Putting in the car key, starting the engine.

Define a remote method after hook

Define a remote method after hook in car.js.

This method is triggered after revEngine finishes execution and prints a message to the console.

Restart the server.

$ ./bin/remote-method-request

You should see:

...
Turning off the engine, removing the key.

Create a boot script

Create print-models.js in the boot directory.

NOTE: The app argument is provided by LoopBack. You can use it to access the application context, which is required when you want to retrieve models, configs, and so on.

Asynchronous boot scripts

To use asynchronous boot scripts, you have to modify boot to take callback. You will also need to provide an additional callback argument in your boot scripts.

Restart the server.

In the server output, you should see:

...
Models:  [ 'User', 'AccessToken', 'ACL', 'RoleMapping', 'Role', 'car' ]
...

Define a model operation hook

Define a model operation hook in car.js.

Copy the create-car.js script to the server/boot directory.

$ cp examples/async-boot-script/create-car.js server/boot/

Restart the server.

You should see:

...
About to save a car instance: { make: 'honda', model: 'civic' }
A `car` instance has been created from a boot script: { make: 'honda', model: 'civic', id: 1 }
...

This model operation hook is triggered before saving any car model instance.

Many other operation hooks are available, such as access, before save, after save, before delete, and after delete. See the model operation hooks documentation for more information.

Add pre-processing middleware

Create the middleware directory to store middleware files.

$ mkdir server/middleware

Create the tracker middleware to respond with the request processing time.

Register the tracker middleware in middleware.json.

We register tracker in the initial phase because we want it configured before other middleware. See the official middleware phases documentation.

Restart the server.

$ ./bin/remote-method-request

You should see:

...
The request processing time is 28.472051 ms.

Your time will be different.

Add post-processing middleware

Create the datetime middleware, which responds with the current date and time when a request is made to localhost:3000/datetime.

Register the datetime middleware in middleware.json.

Create a shell script to test the middleware.

Restart the server.

$ ./bin/datetime-request

You should see:

...
{"datetime":"2015-01-14T22:54:35.708Z"}

Your date and time will be different.

Add an email connector

How do you send email?

  1. Configure an email datasource
  2. Map the built-in Email model to the the email datasource
  3. Send an email using the configured model

Notes:


More LoopBack examples

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