Model Transformer

Requirements

The aim of ModelTransformer is to transform a model e.g., provided by an API to a CoreData model used by the application. For this the transformer has the knowledge of the entity to that the object should be transformed to. Thus this transformers can only be used in conjunction with an NSManagedObjectModel.

Installation

Usage

MTObjectTransformer and MTArrayTransformer are base classes for custom model transformations. Applications using this transformers must therefore subclass these classes to provide their own logic.

The example below transforms all attributes of type NSDateAttributeType using a date formatter to NSDate objects and the attribute with the name 'url' to an NSURL object.

@implementation MyObjectTransformer

- (id)transformedValueForAttribute:(NSAttributeDescription *)attributeDescription
                          ofObject:(id)object 
                          userInfo:(NSDictionary *)userInfo
{
    if (attributeDescription.attributeType == NSDateAttributeType) {
        NSString *dateString = [object valueForKey:attributeDescription.name];
        if (dateString) {
            return [[[self class] dateFormatter] dateFromString:dateString];
        }
        return nil;
    } else if ([attributeDescription.name isEqualToString:@"url"]) {
        NSString *urlString = [object valueForKey:@"url"];
        if (urlString) {
            return [NSURL URLWithString:urlString];
        }
        return nil;
    } else {
        return [super transformedValueForAttribute:attributeDescription
                                           ofObject:object
                                          userInfo:userInfo];
    }
}

@end

In general the transformation is done with the following methods, that can be overwritten in subclasses. The base class will return the value from valueForKey:, if the property is an attribute property, or in case of an relationship property an object of type MTObjectTransformer or MTArrayTransformer, depending on the cardinality (to-one or to-many).

Object Transformer

@interface MTObjectTransformer : NSObject


- (id)transformedValueForAttribute:(NSAttributeDescription *)attributeDescription
                          ofObject:(id)object
                          userInfo:(NSDictionary *)userInfo;

- (id)transformedValueForRelationship:(NSRelationshipDescription *)relationshipDescription  
                             ofObject:(id)object
                             userInfo:(NSDictionary *)userInfo
                                class:(Class)_class;

- (id)transformedValueForRelationship:(NSRelationshipDescription *)relationshipDescription  
                             ofObject:(id)object
                             userInfo:(NSDictionary *)userInfo;

@end

Array Transformer

@interface MTArrayTransformer : NSArray

- (id)transformedObjectAtIndex:(NSUInteger)index
                       ofArray:(NSArray *)array
                      userInfo:(NSDictionary *)userInfo;

- (NSUInteger)transformedCountOfArray:(NSArray *)array
                             userInfo:(NSDictionary *)userInfo;

@end

Author

Tobias Kräntzer, [email protected]

License

Copyright (c) 2014, Tobias Kräntzer All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

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