Realm : How to delete object from RLMArray?

Question

I have created simple relational database (like exists in other dbs) model in the iOS Realm DB. Where i created 2 separate Realm models (tables) user ids with other details and a Wishlist, where the user has an array of Wishlist using RLMArray. Wishlist can contain 1 or more products as in my previous question. In this model table with user ids is constant but Wishlist table of RLMArray can be updated or deleted. I am able to update RLMArray using realm addOrUpdateObject but How can i delete elements from RLMArray? Example relational database model is below :

Code is similar to this :

#import <Realm/Realm.h>

@class User;

// User model
@interface User : RLMObject
@property NSString *name;
@property NSString *user_id;
@property RLMArray< Wishlist *>< Wishlist > *wishlist;
@end

// Wishlist model
@interface Wishlist : RLMObject
@property NSString *id;
@property NSInteger *activity;
@property NSInteger *cost;

@end
RLM_ARRAY_TYPE(Wishlist) // define RLMArray<Person>

// Implementations
@implementation User
@end // none needed

@implementation Wishlist
@end // none needed

Read data from realm :

RLMResults *watchlistDB = [Watchlist allObjects];
WatchlistDB = [realm_data objectAtIndex:index];
RLMArray *realm_array = WatchlistDB.watchlist;

Insert New activity:

User *user_realm = [[MyWatchlistDB alloc] init];
user_realm.user_id = _user_id;
user_realm.name = _user_name;
for (NSDictionary *tempDict in activity)
{
    Wishlist *wishlist_realm = [[Wishlist alloc] init];
    newWatchlist.id =[tempDict objectForKey:@"id"];
    newWatchlist.activity =[tempDict objectForKey:@"activity"];
    newWatchlist.cost = [tempDict objectForKey:@"cost"];

    [user_realm.wishlist addObject:newWatchlist];
}
RLMRealm *realm = [RLMRealm defaultRealm];
[realm beginWriteTransaction];
[realm addOrUpdateObject:user_realm];
[realm commitWriteTransaction];

How can i delete elements from RLMArray ? to update user wishlist when he delete some activities ?

Answer 1

Realm is an object database, not a relational database, so you shouldn't need to implement a foreign key system in order to link objects. If you want to see which User a WishList item belongs, you can use the RLMLinkingObject feature to provide a reverse-lookup instead of what you're doing now.

// Wishlist model
@interface Wishlist : RLMObject
@property NSInteger *activity;
@property NSInteger *cost;
@property (readonly) RLMLinkingObjects *users;
@end
RLM_ARRAY_TYPE(Wishlist) // define RLMArray<Person>

// Implementations
@implementation Wishlist
+ (NSDictionary *)linkingObjectsProperties {
    return @{
        @"users": [RLMPropertyDescriptor descriptorWithClass:User.class 
                                                propertyName:@"wishlist"]
    };
}
@end

This means you can call wishlist.users.firstObject to get the user in which that Wishlist belongs, without needing to do a lot of manual linking work.

Additionally, if you've got a Realm property in User that you want to use to uniquely identify objects, you can explicitly mark that one as a primary key which lets you query for specific objects (Even though we call it a primary key for convinience, it's still not the same as a relational database).

// User model
@interface User : RLMObject
@property NSString *name;
@property NSString *user_id;
@property RLMArray< Wishlist *>< Wishlist > *wishlist;
@end

@implementation User
    + (NSString *)primaryKey {
        return @"user_id";
    }
@end 

User and Wishlist objects are stored in separate tables in Realm, with neither explicitly owning each other (They're just making references). If a Wishlist item is unique to just one User, then you can just delete the Wishlist object from Realm and it will get removed from the RLMArray as well.

To delete all of the wishlist entries belonging to a single user, you could simply do this.

//Get John Smith's entry
User *johnSmith = [User objectForPrimaryKey:@"084"];

//Delete all of the items in John's wishlist
RLMRealm *realm = [RLMRealm defaultRealm]

[realm transactionWithBlock:^{
    [realm deleteObjects:johnSmith.wishlist];
}];

Answer 2

Some how i manage to delete data from realm. Using RLMArray and addOrUpdateObject.

RLMArray<Wishlist> *wishlist_array = Userdb_realm.wishlist; // reading existing data
User *Userdb = [[User alloc] init];
Userdb.user_id = _Userdb_id;
Userdb.name = _Userdb_name;

for (NSString *temp in delArray)
{
    for (int i = 0; i<[wishlist_array count]; i++) {
        Wishlist *wishlistTodel = wishlist_array[i];
        if ([wishlistTodel.user_id isEqualToString:temp]) {
            RLMRealm *realm = [RLMRealm defaultRealm];
            [realm beginWriteTransaction];
            [wishlist_array removeObjectAtIndex:i];
            [realm commitWriteTransaction];
            break;
        }

    }


}
Userdb.wishlist = wishlist_array;
RLMRealm *realm = [RLMRealm defaultRealm];
[realm beginWriteTransaction];
[realm addOrUpdateObject:Userdb];
[realm commitWriteTransaction];

If anyone have better solution can answer here. Thank you for all your response.

Answer 3

From Realm CocoaDocs

- (void)removeObjectAtIndex:(NSUInteger)index