RLMObject as a parent parent class

[SebastianThiebaud]

Hello,

It looks like RLMObject isn't ready to be parent parent of class. It might be not clear, let me explain:

We have a class called ESObject with a lot of features on it. A lot of models inherit of ESObject. As we want use Realm, we use this parenting system:
RMLObject > ESObject > model (ex: ESDiscussion, ESPost, ESComment,...).

The problem is when we want to set a model property, we got this crash:

 *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[RLMStandalone_ESObject setName:]: unrecognized selector sent to instance 0x10b00fdc0'

[alazier]

This is a known limitation - we currently only support object which derive directly from RLMObject. The exception message should have explained this (which in your case it obviously doesn't) - we should be able to get the error message fixed pretty quickly so other people don't suffer from the same confusion.

I hope we will be able to support multiple levels of subclassing in the future - it adds some complexity to the apis and implementation, but I hope we can revisit supporting this after addressing the easier/smaller issues that have been reported since launch.

[SebastianThiebaud]

Do you think moving the ESObject's code into a category of RMLObject is a good idea?

[alazier]

I don't see why that wouldn't work.

[jpsim]

@SebastienThiebaud just be aware that if you add properties to RLMObject through a category using associated objects, those won't be persisted by Realm.

[ghost]

@SebastienThiebaud You can add persisted properties in RLMObject category if you add the properties at runtime before first RLMObject is initialized (for example by filtering the objc_getClassList to subclasses of RLMObject).

example call:

[Class addProperty:@"syncUpdated" Type:@"@\"NSDate\""];

#import "RLMObject+Sync.h"
#import <objc/runtime.h>

@implementation RLMObject (Sync)
@dynamic associatedObject;

NSString *getter(id self, SEL _cmd) {
    return objc_getAssociatedObject(self, @selector(associatedObject)) ;
}

void setter(id self, SEL _cmd, id value) {
    objc_setAssociatedObject(self, @selector(associatedObject), value, OBJC_ASSOCIATION_RETAIN_NONATOMIC) ;
}

+ (void)addProperty:(NSString *)propertyName Type:(NSString *)propertyType
{
    //add properties
    objc_property_attribute_t type = { "T", [propertyType UTF8String]};
    objc_property_attribute_t ownership = { "&", "" };
    objc_property_attribute_t attrs[] = { type, ownership };

    class_addProperty(self, [propertyName UTF8String], attrs, 2);
    class_addMethod(self, NSSelectorFromString(propertyName), (IMP)getter, "@@:");
    class_addMethod(self, NSSelectorFromString([NSString stringWithFormat:@"set%@:", [propertyName capitalizedString]]), (IMP)setter, "v@:@");

}

- (instancetype)initWithSync
{
    //you have to get property names here, because init changes class
    unsigned int propertyCount;
    objc_property_t *properties = class_copyPropertyList([self class], &propertyCount);

    //init has to be called on self to create standalone class
    self = [self init];
    if (self) {
        //default value of property
        for (int i = 0; i < propertyCount; i++) {
            NSString *propertyName = [NSString stringWithCString:property_getName(properties[i]) encoding:NSUTF8StringEncoding];

            //example
            if ([propertyName isEqualToString:@"syncUpdated"]) {
                [self performSelector:NSSelectorFromString([NSString stringWithFormat:@"set%@:", [propertyName capitalizedString]]) withObject:[NSDate date]];
            }
        }

    }

    return self;
}

@end

[alazier]

This should now be possible on master with #940.