Eric Wasylishen, Quentin Mathe
Eric Wasylishen, Quentin Mathe, Christopher Armstrong
MIT License

CoreObject is a version-controlled object database, designed to be a humane persistence layer for applications with a “never lose any work” philosophy.

At the center is an ACID-compliant object store using SQLite, and built on this are semantic merging, rich undo/redo support, collaborative editing, and a transaction API for viewing database snapshots in memory and batching changes for commit.


Build Status

Key Features

  • Revision Control

    • Built on a DVCS (distributed version control system) model
    • Persistent roots have isolated history
      • Comparable to separate Git repositories
    • Based on Object Graph Diff and Merging Model
      • Each Change is a delta represented as an Object Graph Patch
    • Two-level History
      • History Graph per document
      • Undo Track per activity
    • Branch
    • Cheap Copy (copying a document requires O(1) space)
    • Localizable History
    • History Compression and Compaction // Not finished!
    • Serialization Formats
      • JSON and Binary (endian-, 32/64-bit- independent)
      • Stable over multiple invocations for the same object graph (no merge issues in SCM)
      • Integrity Checking (every single committed change includes a checksum)
  • Undo Framework

    • Built on the Revision Control model
      • Never need to define new Command objects
    • Pervasive Undo/Redo
      • Document Changes (Creation, Update and Deletion inside a Document)
      • Store Changes (Document/Branch Creation, Update and Deletion)
    • Selective Undo (each change can be cancelled individually)
    • Persistent Undo Stacks (tree structured/branching undo)
      • Mutiple Undo Views on the same document
      • Undo Stack Union View
  • Object Store

    • Pragmatic OODB atop SQLite
    • Minimalistic Metamodel
    • Flexible Storage Model
      • Coarse-grained Objects with Metadata (e.g. Documents and their Branches)
      • Fine-grained Objects (e.g. inside Document Branches)
      • Optional Object Organization Model based on Tags and Libraries
      • Built-in Indexing and Search (history included)
    • Flexible Collection and Relationship Model
      • Unidirectional or bidirectional
        • Ordered or unordered
        • To-one or to-many
        • Composite
      • Undirectional Unordered Keyed
      • Transparent Constraint Enforcements on Update
    • Cross Document References
      • named branch
      • current branch
      • unidirectional accross arbitrary branch
      • bidirectional between the current branches
    • Synthesized Accessors
    • Transparent Object Graph Copy
    • Transient Object Graph
  • Real-Time Collaboration

    • Any CoreObject-based model supports it (for free)
    • Based on the Revision Control Model
    • Very Fast
    • Full Branch and Undo Support per User
      • Per User Persistent Undo Stack
      • Per User Selective Undo
    • Based on XMPP
  • Overall Design

    • Small Code Base (~ 20 000 loc)
    • Pretty Large Test suite (over 3000 tests)
    • High Quality API documentation
    • Good Debugging Support
      • View object graph in memory as PDF diagram (can be generated from the debugger or in code)
      • Short and Detailed Descriptions for logging objects
    • Minimal dependencies (SQLite and EtoileFoundation)
    • Pervasive UUID use (no string, number or content-based identifiers)
    • Favor JSON formats
    • Create a Persistent Object and save it in 3 loc

        COEditingContext *ctx = [COEditingContext contextWithURL: [NSURL fileURLWithPath: @"TestStore.db"]];
        COPersistentRoot *persistentRoot = [ctx insertNewPersistentRootWithEntityName: @"COObject"];
        [persistentRoot commit];

Build and Install

Clone CoreObject and its dependencies into the same directory (or extract a release .tgz which contains all 3 projects):

git clone
git clone
git clone

The Xcode projects and schemes of interest are:

  • CoreObject/CoreObject.xcodeproj
    • CoreObject – builds the framework itself
    • BasicPersistence – a minimal example app
    • TestCoreObject – the test suite
    • BenchmarkCoreObject – the benchmark
  • CoreObject/Samples/ProjectDemo/ProjectDemo.xcodeproj
    • ProjectDemo – an experimental testbed application with a drawing editor, outliner, and collaborative editing support used in the demo videos
  • CoreObject/Samples/Typewriter/Typerwriter.xcodeproj
    • Typewriter – a reasonably polished note manager that uses CoreObject

For more details, see INSTALL.Cocoa or INSTALL.GNUstep.

Mac OS X support

CoreObject is supported on Mac OS X (10.7 or higher), and iOS support is coming soon.

Warning: Xcode 4.6 or higher is required to build the Xcode projects.