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POUnrecognized selector for NSManagedObject base class
 

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    <p>I am getting an 'unrecognised selector' exception when calling a base-class method on an instance and can't see what the problem is.</p> <p>I have an object called Form as follows:</p> <pre><code>#import &lt;Foundation/Foundation.h&gt; #import &lt;CoreData/CoreData.h&gt; #import "HPSDbBase.h" @interface Form : HPSDbBase @end </code></pre> <p>The base class for Form looks like this:</p> <pre><code>#import &lt;CoreData/CoreData.h&gt; @interface HPSDbBase : NSManagedObject @property (nonatomic, retain) NSString * id; @property (nonatomic, retain) NSString * json; -(id)getJSONElement:(NSString*)key; @end </code></pre> <p>I then try using the Form object within a view controller method as follows:</p> <pre><code>HPSAppDelegate* appDelegate = [[UIApplication sharedApplication] delegate]; NSError* error = nil; NSFetchRequest * request = [[NSFetchRequest alloc] init]; [request setEntity:[NSEntityDescription entityForName:@"Form" inManagedObjectContext:appDelegate.managedObjectContext]]; NSArray* arrayOfForms = [appDelegate.managedObjectContext executeFetchRequest:request error:&amp;error]; for (int i=0;i&lt;arrayOfForms.count;i++) { Form* dbForm = [arrayOfForms objectAtIndex:i]; NSLog(@"Form.json=%@",dbForm.json); // this works NSString* wwwww = (Form*)[dbForm getJSONElement:@"test"]; // exception here } </code></pre> <p>The exception is:</p> <pre><code>-[NSManagedObject getJSONElement:]: unrecognized selector sent to instance 0x8290940 </code></pre> <p>Can anyone see what I'm doing wrong?</p> <p>Thanks a million!</p> <p><strong>EDIT 1</strong></p> <p>Here is the implementation for HPSDbBase:</p> <pre><code>#import "HPSDbBase.h" @implementation HPSDbBase @dynamic id; @dynamic json; -(id)getJSONElement:(NSString*)key { NSData *jsonData = [[self json] dataUsingEncoding:NSUTF8StringEncoding]; NSError *e = nil; id jsonObject = [NSJSONSerialization JSONObjectWithData:jsonData options: NSJSONReadingMutableContainers error: &amp;e]; NSDictionary *jsonDictionary = (NSDictionary *)jsonObject; id rc = [jsonDictionary objectForKey:key]; return rc; } @end </code></pre>
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    2. COI've added the implementation for HPSDbBase, but I thought the problem was that it isn't 'seeing' the object as a Form object, but rather it is 'seeing' it as an NSManagedObject object?
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