Export data from a MongoDB .realm file

2020-06-14

In my case, I had data stored in a Realm file that I needed to re-export to JSON.

First of all we’ll need Realm Studio. Set up, open the Realm file and then export the models, as shown:

Then let’s set up a Node environment:

curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.34.0/install.sh | bash
nvm install 10
## exit and re-enter shell, or run the ./source

Then install the node module:

nvm use 10
npm -g install realm

Great. Now, armed with your list of models, determine your top-level object that you’re extracting from the database. In our case, we are extracting ‘Banana’ type objects.

const Realm = require('realm');

// required for writing our output file
const fs = require('fs');

// this is the 'models' file from Realm
const models = require('./models.js');

function writeObjects(inputRealm, realmName) {
    let a = [];
    for (let item of inputRealm) {
        a.push(JSON.parse(JSON.stringify(item)));
    }
    fs.writeFile(`out/${realmName}.json`, JSON.stringify(a), 'utf8', function(err) {
        if (err) {
            console.log(`error while writing file ${realmName}`)
        }
    });
}

Realm.open(
    {
        schema: [
            models.Banana,
            models.Example,
            models.Example2
        ]
    }
)
.then(
    realm => {
        writeObjects(realm.objects('Banana'), 'Banana');
        // further objects can be written out here of course
        realm.close();
    }
)
.catch(error => {
        console.log(error);
    }
);

To run, make sure you’ve created the output directory mkdir out and then it’s just a case of executing node script.js. Run with switch --inspect-brk and open Chrome at URL chrome://inspect to connect to debugger, pause script execution and inspect runtime vars if need be.

JSON output should be available after execution under ./out.