Check if Realm object already exists

Question

I have a Realm object called Restaurantin my app. This Restaurant object has lots of Table objects connected to it. If I save on, it looks like this:

Restaurant *restaurant = [[Restaurant alloc] init];
restaurant.url = [_userData url];
restaurant.type = [_userData kind];

for (int i = 0; i < [[_userData tables] count]; i++) {
    Input  *input = [[_userData tables] objectAtIndex:i];
    Table *table = [[Table alloc] init];

    table.title = input.title;
    table.seats = input.seats;
    table.type = input.type;

    [restaurant.tables addObject:table];
}

RLMRealmConfiguration *config = [RLMRealmConfiguration defaultConfiguration];
config.fileURL = [NSURL URLWithString:[Preferences getRealmPath]];
RLMRealm *realm = [RLMRealm realmWithConfiguration:config error:nil];

[realm beginWriteTransaction];
[realm addObject:restaurant];
[realm commitWriteTransaction];

Now, what I want is that when a restaurant is added, but it already exists in that configuration, it's not stored. But when the same restaurant is added, but something is different - even if it's the amount of seats at 1 table - it should be added. What's the best way to achieve this?

AustinZ AustinZ · Accepted Answer · 2016-08-01T17:01:43

Realm supports something called primary keys, which seem like a good fit for your problem.

A primary key is a unique identifier for an Realm object; it can be an integer or a string. In your case, you might use the URL as the primary key (if each restaurant is indeed associated with only one URL), or add a new property to serve as the primary key (perhaps a name field).

You can then use the addOrUpdateObject: method instead of the addObject: method. This method only works for object types with primary keys.

In your case, assuming you set up a primary key for your Restaurant model type, Realm would do one of the following:

If the Restaurant was previously added to the Realm and has not changed relative to your new model, nothing will change.
If the Restaurant was previously added to the Realm but your model has since changed, the existing model in the Realm will be updated.
If the Restaurant wasn't previously added to the Realm, it will be added.

Hope that helps.

Check if Realm object already exists

3 Answers