比较Objective-C中的2个对象

Question

In my application, I want to compare 2 core data instances of the entity "Workout". I want to check if the 2 objects have identical attribute values for all of their attributes. Essentially if the two objects are the same minus the relationship, whosWorkout. Is there any way to do this without manually checking every single attribute? I know I could do:

if(object1.intAttr == object2.intAttr){
    NSLog(@"This attribute is the same");
}
else{
    return;
}

repeat with different attributes...

Is there any core data method to make this a bit less tedious?

Answer 1

First I would create an isEqual method in the Workout subclass like this...

-(BOOL)isEqualToWorkout:(Workout*)otherWorkout
{
    return [self.attribute1 isEqual:otherWorkout.attribute1]
        && [self.attribute2 isEqual:otherWorkout.attribute2]
        && [self.attribute3 isEqual:otherWorkout.attribute3]
        && [self.attribute4 isEqual:otherWorkout.attribute4]
        ...;
}

Then whenever you want to compare to Workout objects just use...

BOOL equal = [workout1 isEqualToWorkout:workout2];

Answer 2

You can iterate through the attributes by name.

for (NSString *attribute in object.entity.attributesByName) {
    if ([[object  valueForKey:attribute] intValue] != 
        [[object2 valueForKey:attribute] intValue]) {
       return NO;
    }
}
return YES;

This assumes all integer attributes. You could do a switch statement to check for the class with the class method and deal with different data types as well.

Answer 3

If you need to compare whether one object represents a greater or lesser value than another object, you can't use the standard C comparison operators > and <. Instead, the basic Foundation types, like NSNumber, NSString and NSDate, provide a compare: method:

if ([someDate compare:anotherDate] == NSOrderedAscending) {

    // someDate is earlier than anotherDate

}

Answer 4

I ended up doing the following:

-(BOOL)areEqual:(Workout *)firstWorkout secondWorkout:(Workout *)secondWorkout{
    NSArray *allAttributeKeys = [[[firstWorkout entity] attributesByName] allKeys];

    if([[firstWorkout entity] isEqual:[secondWorkout entity]]
       && [[firstWorkout committedValuesForKeys:allAttributeKeys] isEqual:[secondWorkout committedValuesForKeys:allAttributeKeys]]) {
        return YES;
    }
    else{
        return NO;
    }
}