RealmFire for Swift

RealmFire's aim is to automatically sync a local realm database with firebase.

NOTE! This is an inofficial library which currently is nothing more then a proof of concept. Feel free to post issues if you have any feedback or let me know that you aim to use it and for what.

The library offers similar functionality as the Realm Mobile Platform which is the official realm sync solution and is the better choice in most cases. RealmFire is useful when you are already invested in firebase or if you are developing a service for platforms not supported by Realm Mobile Platform such as the web.

The advantage of using realm, and not only the firebase sdk, is that you get an offline first application. It will sync data when network is available, but it can handle months without any connection if necessary.

Integration

1. Download the repository and add the RealmFire folder to your project (package manager support is WIP, see #1)
2. Extend SyncObject instead of Object to map that class to a firebase collection
3. After updating a realm object, call RealmFire.markForSync(object) or RealmFire.markForDeletion(object) in a write transaction to sync that object the next sync.
4. Call RealmFire.sync() to sync. This will both fetch changes from firebase and upload local changes.

Only tested with Swift 3, RealmSwift 2.4.2 and Firebase SDK 3.12.0

Usage example

Below is a minimal usage example. Take a look at the the demo project for more details.

// Person.swift
class Person: SyncObject {
    dynamic var name = ""
    dynamic var age = 0
}

// ViewController.swift
let realm = try! Realm()
try! realm.write {
    let person = realm.create(Person.self)
    person.name = "John"
    person.age = 25
    RealmFire.markForSync(person)
}

// The sync call attempts to sync all changed objects and fetch changed firebase objects
RealmFire.sync(realm, firDatabase)

Reference

RealmFire.swift

The main class containing all public api methods

• RealmFire.sync() Uploads local changes and fetches firebase updates
• RealmFire.markForSync(objects) Adds the specified SyncObjects to the sync queue.
• RealmFire.markForDeletion(objects) Adds the specified SyncObjects to the deletion queue.

SyncObject.swift

A SyncObject is an Object which maps to a specific firebase collection.

• primaryKey() The primary key of a realm object will also be used as primary key for the firebase collection. Required to be overriden by SyncObject subclasses.
• collectionName() Override to specify a custom firebase collection name. Default is the class name.
• customAttributes() Override to specify custom attribute name mappings between firebase and realm.
• encode(prop: Property) and decode(prop: Property) Override for customized object encoding/decoding
• uploadedAtAttribute() Override to rename the attribute which the library uses to query only changed objects

Sync Error Behavior

The default behavior of RealmFire is to silently ignore errors. If you want to show the user that an error occured you can set a custom error reporter with RealmFire.setErrorHandler().

Sync Behavior

This library automatically resolves sync conflicts with a best guess attitude. Currently this means that the object which is last sent to firebase will always win. There are plans to implement a somewhat better sync strategy based on when objects were modified, see #2.

RealmFire handles deletions by adding a deleted_at flag to each object and then syncing this to clients.

Before alpha release

• Change SyncMeta to dictionary based
• Sync deletions from firebase to realm (force soft delete?)
• Write inline code comments for design descisions
• Tests for Syncer
• Tests for Meta
• Make sure Mapper tests make sense

Future work

• Research how to add lib to cocoa pods, see complications here CocoaPods/CocoaPods#5368
• Make it possible to ask lib about syncing status
• Sync subsets of SyncObject classes to different firebsae apps
• Add way to not force user to create Object subclasses for readonly objects
  • The idea is to use Mapper to convert between Dictionary and Object
  • Will probably be repressented by the Object subclass DataObject
• Wait to apply changes until all relationships are fetched (udpatedAt prop)
• Consider helping user setup automatic sync
• Consider adding option for syncing when internet is back

Contributions

I will most likely not merge any pull request until I have decided upon an initial design for the API. Feel free fork the library and use the code however you wish however.