CODEWITHSUNDEEP
realm
Cuong Ly
Cuong Ly

Reputation: 11

How can query nested object in Realm DB with Objective C

I'm researching how to use Realm DB for my new project and I got some issues. Please share your experiences when you worked on Realm DB. Sorry about my long question list.

First, please refer my sample code

Dog class

Dog.h
@interface Dog : RLMObject

@property NSString *name;
@property NSInteger age;

@end

RLM_ARRAY_TYPE(Dog) // define RLMArray<Dog>

And Person class

Person.h
@interface Person : RLMObject

@property NSString             *name;
@property NSInteger             age;

// to-many relationship
@property RLMArray<Dog *><Dog> *dogs;

@end

RLM_ARRAY_TYPE(Person) // define RLMArray<Person>

Then, I create data for person and dog (1000000 records) - 1 person will have 1-many dogs. And I got stuck in some cases

  1. How to get people have dog with dog name is "Rex"? I research it but there is no guide for objective C

  2. The performance in deleting an object seems to be slow I tried to delete person has a name is "Ethan" and performance is slow and crash app when it execute a half list. I guess I used incorrect way to delete object.

    RLMResults *people = [Person objectsWhere:@"name == 'Ethan'"];
// Get the default Realm
RLMRealm *realm = [RLMRealm defaultRealm];

[realm beginWriteTransaction];

for (int i=0; i< people.count; i++) {
    Person *aPerson = [people objectAtIndex:i];
    [realm deleteObject:aPerson];
}

[realm commitWriteTransaction];

The result is >52000 record with have a name is "Ethan" and app only delete a half of them (26000)

  1. I don't know how to delete record with condition with Realm. I think I will write the code like below for my question #2

    [Person deleteWhereObject:@"name = 'Ethan'"];

  2. It is not yet clear on how can rename, delete or add new column to the DB after it is created (apart from using the most simple way which is delete the DB and recreate it again)

  3. The tools (Realm browser) for browsing the data file created on desktop doesn't provide much flexibility in querying data. It only allow browse through the data but not allow querying using a certain condition. Please guide me to query data with this tool if I lost something.

  4. For troubleshooting, may be I have existing DB from client app and I want to import it in my project to troubleshoot client's bugs. So, how can I do it with Realm DB?

  5. After insert 1000000 records for Person and Dog table, DB size is 52.8 MB. But DB size increase to 92.3 MB after I call delete all data 

    // delete all object
[realm beginWriteTransaction];
[realm deleteAllObjects];
[realm commitWriteTransaction];

Then, I insert data again and file size continue to increase. I don't know what's wrong in my steps.

Hope getting your support soon!

Upvotes: 1

Views: 1555

Answers (1)

marius
marius

Reputation: 7806

  1. RLMResults *people = [Person objectsWhere:@"ANY dogs.name == 'Rex'"];

  2. Use deleteObjects: with the retrieved RLMResults instead of deleting every single object yourself. If you enumerate, I'd recommend to use NSFastEnumeration with for (… in …). Note that RLMResults are auto-updated, so if you do concurrent changes, then you can run into surprises.

  3. See my answer for question 2.

  4. Change your schema, bump the schemaVersion of your RLMRealmConfiguration and provide a migration block, if you rename properties or change their type.

  5. This isn't possible yet, but still in the making. This is tracked by issue #28 in the realm-browser-osx repo.

  6. Put the realm file in the app bundle and copy it at runtime into the user data directory (e.g. RLMRealm.defaultConfiguration.path), if you want to be able to write to the file.

  7. The file size blows up, because no compaction is happening. You can enforce that by writing a compacted copy with writeCopyToPath:. You could do this e.g. at app start, because otherwise it can be non-trivially to make sure that all RLMRealm instances are teared down before.

Upvotes: 2

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