PouchDB Advanced Transform Library

Apply a transform function to documents before and after they are stored in the database. These functions are triggered invisibly for every get(), put(), post(), bulkDocs(), allDocs(), changes() before or after, and also to documents added via replication.

This allows you to:

• Encrypt and decrypt sensitive document fields
• Compress and uncompress large content (e.g. to avoid hitting browser storage limits)
• Remove or modify documents before storage (e.g. to massage data from CouchDB)

Note: This plugin is modified from transform-pouch to enhance it's ability:

• add the afterIncoming and beforeOutgoing hook.
  • incoming is triggered before saving to database.
    • returns must be an object with doc attribute.
      • can pass through extra options in the object to next hook.
  • afterIncoming is triggered after saving.
  • beforeOutgoing is triggered before getting from database.
  • outgoing is triggered after getting from database.

Note: This API has not been stable yet. beforeOutgoing has not applied to all methods.

Usage

npm install pouchdb-transform

And then attach it to the PouchDB object:

import PouchDB from 'pouchdb'
import transformPlugin from 'pouchdb-transform';

PouchDB.plugin(transformPlugin)

API

When you create a new PouchDB, you need to configure the transform functions:

var pouch = new PouchDB('mydb');
pouch.transform({
  async incoming(doc, args: IPouchDBWrapperArgs, type: TransformPouchType): ITransformIncomingResult {
    // do something to the document before storage
    return {doc, ...};
  },
  afterIncoming(result: ITransformIncomingResult, type: TransformPouchType): void {
    if (result.ok) {
      // do something to the successful document after storage
    } else {
      // the failed document to save.
    }
  },
  beforeOutgoing(docId: any, args: IPouchDBWrapperArgs, type: TransformPouchType): BeforeOutgoingReturn {
    // do something to the document before retrieval
    // it will skip retrieval and use it as doc if returns
    return this.fCache.get(docId);
  },
  async outgoing(doc: IDoc,
                 args: IPouchDBWrapperArgs,
                 type: TransformPouchType): IDoc {
    // do something to the document after retrieval
    return doc;
  }
});

Notes:

• You can provide an incoming function, an outgoing function, or both.
• Your transform function must return the document itself, or a new document (or a promise for such).
• incoming functions apply to put(), post(), bulkDocs(), and incoming replications.
• outgoing functions apply to get(), allDocs(), changes(), query(), and outgoing replications.
• The incoming/outgoing methods can be async or sync – just return a Promise for a doc, or the doc itself.