06

6 - Writing messages

An essential part of the API of Sage is the possibility to write messages in the db.

Hyperdb provides different methods for writing data in the db, one of these is:

  db.put(key, value, cb)

Like we said earlier, hyperdb is a key-value database, that means if we execute .put('/test', 'hi!') the valu stays saves in the key /test.

🔬 See the / that we add to the key? Hyperdb has support for namespaces similar to redis.

We can, for example, read all the values related to a particular namespace and their subfolders:

db.put('/test/1', 'hi')
db.put('/test/2', 'how are you?', () => {
  db.createReadStream('/test').pipe(printInConsole)
})

// console:
// [ Node(key=test/1, value='hi', seq=1, feed=0)) ]
// [ Node(key=test/2, value='how are you?', seq=2, feed=0)) ]

Exercise

Define two new instance methods for Saga

1. ready -> Promise A method that returns a promise and that can resolve itself when the db is ready.
2. writeMessage(message: string) -> Promise A method that receives as a parameter a string and returns a Promise.

But we have to take into account a few more things:

• The promise resolves itself when it terminates the writing operation and has returned the message key If the writing fails, we have to make a reject with the error
• We can't just save the message if we don't also have aditional information over the same key: { key, message, username, timestamp }
• The messages have to be saved below the namespace /messages/<messageKey>.
• The keys have to be unique.

Tips

• The best way to define a unique key is to use some ID generator. We recommend that you look at hyperid

Test

$ npm test ./06

test.js

Solution

solution.js