Mantle + Core Data: this class is not key value coding-compliant for the key

Question

I'm trying to use Mantle and Core Data to build a client for reddit but I keep getting *** Caught exception setting key "upvotes" : [<Thread 0x14c61ba10> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key upvotes. thrown and I can't figure out what's wrong...

I don't think I've missed out anything from the Mantle docs.

Thread+CoreDataProperties.h

#import "Thread.h"

NS_ASSUME_NONNULL_BEGIN

@interface Thread (CoreDataProperties)

@property (nullable, nonatomic, retain) NSString *approvedBy;
@property (nullable, nonatomic, retain) NSNumber *isArchived;
@property (nullable, nonatomic, retain) NSString *author;
@property (nullable, nonatomic, retain) NSString *title;
@property (nullable, nonatomic, retain) NSDate *createdDate;
@property (nullable, nonatomic, retain) NSString *subreddit;
@property (nullable, nonatomic, retain) NSString *domain;
@property (nullable, nonatomic, retain) NSNumber *upvotes;

@end

NS_ASSUME_NONNULL_END

Thread+CoreDataProperties.m

#import "Thread+CoreDataProperties.h"

@implementation Thread (CoreDataProperties)

@dynamic approvedBy;
@dynamic isArchived;
@dynamic author;
@dynamic title;
@dynamic createdDate;
@dynamic subreddit;
@dynamic domain;
@dynamic upvotes;

@end

Thread.h

@import Foundation;
@import CoreData;
@import Mantle;
@import MTLManagedObjectAdapter;

NS_ASSUME_NONNULL_BEGIN

@interface Thread : MTLModel <MTLJSONSerializing, MTLManagedObjectSerializing>

// Insert code here to declare functionality of your managed object subclass

@end

NS_ASSUME_NONNULL_END

#import "Thread+CoreDataProperties.h"

Thread.m

#import "Thread.h"
#import <Mantle/MTLValueTransformer.h>

@implementation Thread

#pragma mark MTLManagedObjectSerializing Protocols

+ (NSString *)managedObjectEntityName
{
    return @"Thread";
}

+ (NSDictionary *)managedObjectKeysByPropertyKey
{
    return @{
             @"approvedBy": @"approvedBy",
             @"isArchived": @"isArchived",
             @"author": @"author",
             @"title": @"title",
             @"createdDate": @"createdDate",
             @"subreddit": @"subreddit",
             @"domain": @"domain",
             @"upvotes": @"upvotes"
             };
}

+ (NSSet *)propertyKeysForManagedObjectUniquing {
    return [NSSet setWithObjects:@"approvedBy",@"isArchived",@"author",@"title",@"createdDate",@"subreddit",@"domain",@"upvotes", nil];
}

#pragma mark MTLJSONSerializing Protocols

+ (NSDictionary *)JSONKeyPathsByPropertyKey {
    return @{
             @"approvedBy": @"approved_by",
             @"isArchived": @"archived",
//             @"author": @"author",
//             @"title": @"title",
             @"createdDate": @"created",
//             @"subreddit": @"subreddit",
//             @"domain": @"domain",
             @"upvotes": @"ups"
             };
}

+ (NSValueTransformer *)JSONTransformerForKey:(NSString *)key {
    if ([key isEqualToString:@"createdDate"]) {
        return [Thread dateJSONTransformer];
    }

    return nil;
}

+ (NSValueTransformer *)dateJSONTransformer {
    return [MTLValueTransformer transformerUsingForwardBlock:^id(NSNumber *unixTimestamp, BOOL *success, NSError *__autoreleasing *error) {
        return [NSDate dateWithTimeIntervalSince1970:unixTimestamp.doubleValue];
    } reverseBlock:^id(NSDate *date, BOOL *success, NSError *__autoreleasing *error) {
        return [NSNumber numberWithDouble:[date timeIntervalSince1970]];
    }];
}

@end

Answer 1

I can't see how your declaration of Thread class relates to NSManagedObject. You've re-declared it as MTLModel, which is subclass of NSObject. Of course it have no upvotes or any other property defined in CoreDataProperties category since those properties are dynamic, and there will be no Core Data runtime support to provide implementation for them.

You should undo that change to Thread.h, or just delete those four files and recreate them with Xcode.

And about Mantle: I don't think that it directly supports Core Data. See here.