# How to build an API

## 1. Check the requirement

- api endpoint
- expected response object

## 2. Create the route

- go to `/mern/api/routes/map.routes.js`

- add an new route
- for get
`app.get("/api/map/total", controller.totalMap);`
- for post
` app.post("<your route name>", controller.function)`
1. The controller here means "/controllers/map.controller"
2. The function here is a function that is going to handle your request in controller.js.

const controller = require("../controllers/map.controller");

module.exports = function (app) {
    app.use(function (req, res, next) {
        res.header("Access-Control-Allow-Headers", "x-access-token, Origin, Content-Type, Accept");
        next();
    });

    app.get("/api/map/total", controller.totalMap);

    > put your new route here
};

## 3. Make the model(& DB)

Image that, a model is a table.

- go to `mern/api/models` create a js file under this folder.
e.g. `MODEL_NAME.model.js`
- Define the MODEL (just like a table in mongoDB)
you just need to
1. change MODEL_NAME into your model name
2. Define the fields this table needs

const mongoose = require("mongoose");

const MODEL_NAME = mongoose.model(   // replace MODEL_NAME
    "MODEL_NAME",  // replace MODEL_NAME
    new mongoose.Schema({
        field2: String,  // edit here
        field3: Number,  // edit here
        // you don't need to define id here, mongo DB will auto create for us.
    })
    
);

module.exports = MODEL_NAME;   // replace MODEL_NAME

## 4. Regiter you model

- to go `/mern/api/models/index.js`
- find this part

db.user = require("./user2.model");
db.role = require("./role.model");
// register you model here-------

// register your model here
db.MODEL_NAME = require("./MODEL_NAME.model");

//------------------------------

After this step, you can use db.MODEL_NAME to interact with mongoDB.

## 5. Import the model that you created and make the function in controller

- go to `/mern/api/controllers/map.controller.js`
- add an new function in this format

exports.your_function_name = (req, res) => {
// 5-1 get data 

// 5-2 save data 

}

### 5-1 Get data from DB

- [findOne](https://docs.mongodb.com/manual/reference/method/db.collection.findOne/) by consiton

Model.fineOne({condition}).exec((err,data)=>{
   if (err) {
      res.status(500).send({ message: err });
      return;
   }
   const obj={
      id: data.id,
      username: data.username,
      email: data.email,
   }
   res.status(200).send(obj);
})

e.g.

User.findOne({
username: req.body.username,
})
.exec((err, user) => {
if (err) {
res.status(500).send({ message: err });
return;
}
res.status(200).send({
id: user.\_id,
username: user.username,
email: user.email,
roles: authorities,
accessToken: token,
});

        })

- find

Model.find({condition}).exec((err,data)=>{
   if (err) {
      res.status(500).send({ message: err });
      return;
   }
   res.status(200).send(data);
})

### 5-2 save data in DB

- create a new model instance
- model.save and response the frontend

    const user = new User({
        username: req.body.username,
        email: req.body.email,
        password: bcrypt.hashSync(req.body.password, 8),
    });

    user.save((err, user) => {
        if (err) {
            res.status(500).send({ message: err });
            return;
        }
        res.status(200).send(user);
    }

## 7. check your API works successfully

- run `docker-compose up --build` in terminal
if it success, you will see:
- open Postman
- create a new request
- set GET or POST
- http://localhost:8080/<the api endpoint>
e.g. http://localhost:8080/api/auth/signup
- press down the Send button
- if you need to post data
1. Choose Body
2. select "row"
3. select "JSON" via dropdown list
4. Edit the data that you want to store

      {
         "username":"abc",
         "email":"[e-mail]",
         "password":"12345",
         "roles":["user"]
      }

if you get data successfully, congratulations! You complete you API!

---
## Example
### Edited Files:

- route
mern/api/routes/map.routes.js

- model
mern/api/models/index.js
mern/api/models/example.model.js

- controller
mern/api/controllers/example.controller.js

### Result:
- create one

- find all

- find by name