Add the ability to apply a transformation function to documents before backup or restoration

Add a "schema migration" feature that add the ability to apply a transformation function before either writing to disk (so user can verify the schema migration) or before restoring to Firestore.

The proposal idea is to have a flag for this, called --transformFn or -T for the command line, where the user can indicate the path of a file from where the transformation function will be exported.

And for example will be executed like this:

firestore-backup-restore --accountCredentials cred.json --backupPath backups --transformFn transformFn.js

This transformation function should return a promise, and receive a object as parameter, which will contain the following fields:

accountDb {Object} Firestore database instance from where the backup is made restoreAccountDb {Object} Firestore database instance where the backup is restored collectionPath {Array} Array that contains the path of the collection docId {String} Id of the document, where the function will be applied docData {Object} Document data with "backup" format, specified below*

docData will have the format NAME: { "value": VALUE, "type": TYPE }, For example:

Task {
  "name": { "value": "Buy some apples", "type": "string" }
  "difficulty": { "value": "easy", "type": "string" },
}

The allowed types are: 'string', 'number', 'boolean', 'object', 'array', 'null', 'timestamp', 'geopoint', 'documentReference'

Example of transformation function:

To rename a field called MyCompany, to company in all the documents of Companies


const transformFn = async ({
accountDb,
restoreAccountDb,
collectionPath,
docId,
docData
}) => {
const operationByCollection = {
Companies: function(companyDoc) {
  const docResult = companyDoc;
  if (!companyDoc.MyCompany) return Promise.resolve(docResult);
  docResult.company = {
    value: docResult.MyCompany.value,
    type: 'documentReference'
  };
  delete docResult.MyCompany;
  return Promise.resolve(docResult);
}  
};
const collectionName = collectionPath[collectionPath.length - 1] // take the last one
if (!operationByCollection[collectionName]) {
console.log(`There is not a transformation for ${collectionName}`);
return docData;
}
return await operationByCollection[collectionName](docData);
};

export default transformFn;

willhlaw / node-firestore-backup-restore

Add the ability to apply a transformation function to documents before backup or restoration #30