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Offline Mode Identifier Handling

3 posts · Feb 2017 – Mar 2017

What this trail covers

Trello's offline mode has been implemented, with the database acting as a simulacrum of the Trello server. Changes made offline are stored locally and will be synced with Trello servers in subsequent articles. The system handles local, client-generated IDs and server-assigned IDs, distinguishing between them using a 'local-server barrier' architecture and an annotation-based ID converter. The current implementation focuses on managing deltas for syncing offline changes.

All Atlassian trails
  1. The two ID problemThis post details the challenges and solutions for managing dual identifiers (local and server-assigned) in Trello's offline mode. It describes two failed approaches (switching IDs and mapping tables) and introduces the 'local-server barrier' architecture. A key technical contribution is the annotation-based ID converter for transforming models between local and server ID schemes, highlighting its reliance on mutable data.
  2. Syncing changesThis post details the construction and upload of deltas for syncing offline changes made in Trello's mobile applications. It describes the delta structure, which includes entries for model changes and individual field modifications (deltas), and explains how an annotation-based calculator on Android automatically computes these differences. The post also outlines the process of uploading these deltas to the server in the order they were created to maintain data hierarchy, converting them into generalized HTTP POST requests.
  3. Airplane mode: enabling Trello mobile offlineThis post details the initial architectural changes for Trello's mobile offline mode, focusing on the Android app. It describes the shift from an online-only architecture (UI interaction directly triggering network requests) to an offline-first architecture where the local database becomes central. The database now acts as a simulacrum of the Trello server, and the network portion is optional. Two key changes are highlighted: making the database mimic the server's logic and implementing a system to sync changes with Trello servers (to be detailed in a future post). The post also introduces the concept of handling local vs. server-assigned identifiers, with a 'local-server barrier' and an annotation-based ID converter.