Tutorial part-2: Key-value store - basic operations

A key-value store has three basic operations: get, set and delete.
This makes it easy and efficient to insert, look up, update and remove data, as you only need to know the key to access the corresponding value.
In this (part-2) tutorial we'll show how to use the simple key-value store API operations in serverless JavaScript functions.

Read the tutorial part-1 here

Setting and getting values in the key-value store

Inserting (set) a new value in the key-value store requires a unique key string and an arbitrary string value.

'key' => 'one 2 three'

The API for setting and getting a value in the key-value store is shown in the code example below:

// Connect to the key-value store
const db = await Datastore.open();
// set key-value
await db.set('mykey', 'My value');
// get value
const result = await db.get('mykey');
console.log(result);

Output from the console.log statement:

My value

The db.set(key, value, options={}) API has an options part > which lets you add a TTL value and a keyspace parameter.
This is covered more in the part-5/6 of this tutorial.

Set a JSON value

Setting a JSON value in the key-value store is easy. Use the JSON.stringify function to convert your JavaScript object to a string value before inserting the value to the store. And use the JSON.parse function to convert it back to an Object when retrieving the value.

const myObj = {
    "foo": "bar",
    "price": 42
};  
const db = await Datastore.open();
// convert JSON to string
await db.set('myjsonkey', JSON.stringify(myObj));
// get value from key
const result = await db.get('myjsonkey');
// convert back to Object
console.log(JSON.parse(result));

Output from the console.log statement:

{ foo: 'bar', price: 42 }

Set a binary value

Using the Node.js Buffer library we can set any string or binary value into the key-value store. Converting a buffer value to a hex string is a perfect solution for this use case.

  const db = await Datastore.open();
  // create a hex value from a Buffer
  const myBufVal = Buffer.from('Hello world!😎😎😎', 'utf-8').toString('hex');
  // set value
  await db.set('mybufkey', myBufVal);
  // get the value for key
  const hexString = await db.get('mybufkey');
  // convert hex string value back to a normal string
  const stringVal = Buffer.from(hexString, 'hex').toString();
  console.log(hexString, stringVal);

Output from the console.log statement:

48656c6c6f20776f726c6421f09f988ef09f988ef09f988e Hello world!😎😎😎

Set a number value

Numbers are converted to its string representation.

const db = await Datastore.open();
// set value as Integer
await db.set('mynumkey', 42);
// get value for key
const result = await db.get('mynumkey');
console.log(result, 'is of type', typeof result);

Output from the console.log statement:

42 is of type string

Setting multiple values

In some use cases you'll need to insert or set multiple values to the key-value store.
JavaScript solves this task for us with the Promise.all function. The key-value store set function returns a Promise, hence we can create an array of set functions that we pass to the Promise.all function. The code example below shows you how we can create multiple key-value inserts in one operation.

const db = await Datastore.open();
const array = [
  db.set('uno', 'one value'),
  db.set('dos', 'two value'),
  db.set('tres', 'three value')
]
const result = await Promise.all(array);
console.log(result);

Output from the console.log statement:

[ 'one value', 'two value', 'three value' ]

Getting multiple values

Similar to the technique we use for setting multiple values in the key-value store, we can also get multiple values with the Promise.all function.

const db = await Datastore.open();
const array = [
  db.get('uno'),
  db.get('dos'),
  db.get('tres')
]
const result = await Promise.all(array);
console.log(result);

Output from the console.log statement:

[ 'one value', 'two value', 'three value' ]

Deleting values

Deleting values from the key-value store follows the same pattern as the get operation.
When deleteting a key-value pair, the value is returned if the key exists, otherwise a null value is returned. You can also use the Promise.all technique shown above for multiple delete operations. The code example below shows the basic delete operation.

const db = await Datastore.open();
// delete key-value pair
const result1 = await db.del('uno');
// try to get the deleted key, should be null
const result2 = await db.get('uno');
console.log(result1, result2);

Output from the console.log statement:

uno null

This part-2 of the key-value store tutorial has shown how you can use the basic operations in serverless JavaScript functions with codehooks.io.

The next Part-3: Increment end decrement.