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Alex Rupérez

Published: 03 Oct 10:37
I starred matthewcheok/Realm-JSON at GitHub.
A concise Mantle-like way of working with Realm and JSON.
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Realm+JSON License MIT

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A concise Mantle-like way of working with Realm and JSON.

Breaking Change

  • Method - deepCopy replaces the previous functionality of - shallowCopy, which no longer maintains an object's primary key
  • Updated to use native primary key support in Realm 0.85.0
  • Update your code to use methods -createOrUpdateInRealm:withJSONArray: or -createOrUpdateInRealm:withJSONDictionary:
  • You must wrap these methods in a write transaction (between [realm beginWriteTransaction]; and [realm commitWriteTransaction];)
  • These methods call -createOrUpdateInRealm:withObject: behind the scenes for performance.


Add the following to your CocoaPods Podfile

pod 'Realm+JSON', '~> 0.2'

or clone as a git submodule,

or just copy files in the Realm+JSON folder into your project.

Using Realm+JSON

Simply declare your model as normal:

typedef NS_ENUM(NSInteger, MCEpisodeType) {
    MCEpisodeTypeFree = 0,

@interface MCEpisode : RLMObject

@property NSInteger episodeID;
@property NSInteger episodeNumber;
@property MCEpisodeType episodeType;

@property NSString *title;
@property NSString *subtitle;
@property NSString *thumbnailURL;

@property NSDate *publishedDate;



Then pass the result of NSJSONSerialization or AFNetworking as follows:

  [MCEpisode createOrUpdateInRealm:[RLMRealm defaultRealm] withJSONArray:array];


  [MCEpisode createOrUpdateInRealm:[RLMRealm defaultRealm] withJSONDictionary:dictionary];

Use the -JSONDictionary method to get a JSON-ready dictionary for your network requests.


You should specify the inbound and outbound JSON mapping on your RLMObject subclass like this:

+ (NSDictionary *)JSONInboundMappingDictionary {
  return @{
         @"episode.title": @"title",
         @"episode.description": @"subtitle",
         @"": @"episodeID",
         @"episode.episode_number": @"episodeNumber",
         @"episode.episode_type": @"episodeType",
         @"episode.thumbnail_url": @"thumbnailURL",
         @"episode.published_at": @"publishedDate",

+ (NSDictionary *)JSONOutboundMappingDictionary {
  return @{
         @"title": @"title",
         @"subtitle": @"episode.description",
         @"episodeID": @"id",
         @"episodeNumber": @"episode.number",
         @"publishedDate": @"published_at",

JSON preprocessing can be done by implementing jsonPreprocessing: static method:

- (NSDictionary *)jsonPreprocessing:(NSDictionary *)dictionary {
    NSMutableDictionary *dict = [[NSMutableDictionary alloc] initWithDictionary:dictionary];
    dict[@"releaseCount"] = @(0);
    return dict.copy;

Leaving out either one of the above will result in a mapping that assumes camelCase for your properties which map to snake_case for the JSON equivalents.

As you can do with Mantle, you can specify NSValueTransformers for your properties:

+ (NSValueTransformer *)episodeTypeJSONTransformer {
  return [MCJSONValueTransformer valueTransformerWithMappingDictionary:@{
              @"free": @(MCEpisodeTypeFree),
              @"paid": @(MCEpisodeTypePaid)

Working with background threads

Realm requires that you use different RLMRealm objects when working across different threads. This means you shouldn't access the same RLMObject instances from different threads. To make this easier to work with, use - primaryKeyValue to retrieve the wrapped primary key value from an instance and query for it later using + objectInRealm:withPrimaryKeyValue:.

id primaryKeyValue = [episode primaryKeyValue];
dispatch_async(dispatch_get_main_queue(), ^{
    MCEpisode *episode = [MCEpisode objectInRealm:[RLMRealm defaultRealm] withPrimaryKeyValue:primaryKeyValue];

    // do something with episode here

Working with (temporary) copies (RLMObject+Copying)

If you need to display UI that may or may not change an object's properties, it is sometimes useful to work with an object not bound to a realm as a backing model object. When it is time to commit changes, the properties can be copied back to the stored model.

Methods - shallowCopy and - mergePropertiesFromObject: are provided. The later of which needs to be performed in a realm transaction.

#import <Realm+Copying.h>

MCEpisode *anotherEpisode = [episode shallowCopy];
anotherEpisode.title = @"New title";

// ...

[episode performInTransaction:^{
    [episode mergePropertiesFromObject:anotherEpisode];

Additionally, method - deepCopy is provided. Unlike - shallowCopy, it maintains the object's primary key.


Realm+JSON is under the MIT license.