Get random docs from PouchDB (or CouchDB)

Question

I'm designing a quiz app with Angular and Ionic. I have about 2000 questions in json format and I choose PouchDB as database. CouchDB is perfect for me: I can add new question on a server and app auto update question and answer.

But I have a doubt now: I cannot find a way to get random docs from Pouch. With my app I will generate quizzes from some selected section and I must get a variable number of docs from my DB.

I'm using the db.allDocs([options], [callback]) api, I can set a limit but I cannot find a way to get random doc.

Is there any solution?

Answer 1

The first solution given by @nlawson isn't always working, for example I had to delete every document fetched so I lose the sequence of IDs, for example:

I had a list of documents with ids from 1 to 5

1- random is 3

2- get document with id 3

3- delete document with id 3 State of the database [1,2,4,5]

4- if random is anything but 3 repeat steps above, but if random is 3 or any id already deleted it cause problems, so this solution wasn't working, so I found another solution which is:

ANSWER:

Using the Mango querie find(), with this code

let rand = Math.floor(Math.random() * (max - min + 1)) + min;

db.find({
   selector: {_id: {$gte : '1'}},
   limit : 1,
   skip : rand-1,
});

First of all I get a random number, the max is the number of documents in my database and the min is 1 as the first id given to the first document.

After that I execute the find() query to select documents with an id great or equal to 1 (basically all), limit the query to retrieve only the first and start retrieving from rand-1.

To reuse our first example with rand equal 3 it will be something like that:

1- get all documents with an ID great or equal 1 => [1,2,3,4,5]

2- starting from rand-1 witch is 3-1=2 get the a limited number of documents the limit is 1 => [2]

So it will always return the document on the position rand.

P.S: to use find() you must install on top of pouch this library pouchdb.find.js