How to omit null values in JSON Dictionary using Mantle? - ios

Question

I have MyModel inheriting from MTLModel (using the GitHub Mantle pod).
MyModel.h
#import <Mantle/Mantle.h>
#interface MyModel : MTLModel <MTLJSONSerializing>
#property (nonatomic, copy, readonly) NSString *UUID;
#property (nonatomic, copy) NSString *someProp;
#property (nonatomic, copy) NSString *anotherProp;
#end
MyModel.m
#import "MyModel.h"
#implementation MyModel
+ (NSDictionary *)JSONKeyPathsByPropertyKey
{
return #{
#"UUID": #"id",
#"someProp": #"some_prop",
#"anotherProp": #"another"
};
}
}
#end
Now I want to send the JSON to the backend using AFNetworking. Before that I convert the model instance to a JSON NSDictionary to use as parameters/body payload within my request.
NSDictionary *JSON = [MTLJSONAdapter JSONDictionaryFromModel:myModel];
But this JSON consists of strange "" Strings for properties of my model that are nil. What i instead want is Mantle to omit these key/value pairs and just spit out a JSON with only the properties that are not nil or NSNull.null, whatever.

Answer 1

This is a common issue with Mantle and it's called implicit JSON mapping.
MTLJSONAdapter reads all properties of a model to create a JSON string optionally replacing property names with ones given in +JSONKeyPathsByPropertyKey.
If you want some properties to be excluded from the JSON representation of your model, map them to NSNull.null in your +JSONKeyPathsByPropertyKey:
+ (NSDictionary *)JSONKeyPathsByPropertyKey {
return #{
#"UUID": #"id",
#"someProp": #"some_prop",
#"anotherProp": #"another",
#"myInternalProperty": NSNull.null,
#"myAnotherInternalProperty": NSNull.null,
};
}
The implicit JSON mapping has lately become a noticeable problem, a solution for which is currently being discussed at Mantle's home repository at GitHub.
See issues #137, #138, #143 and the current discussion under #149.
EDIT: I clearly misunderstood the question, but now, when I suppose I understand it correctly, the answer is simple.
MTLJSONAdapter generates the JSON data using MTLModel's dictionaryValue property. If you wish to exclude a property from the JSON itself, you can overwrite that method in your MYModel:
- (NSDictionary *)dictionaryValue {
NSMutableDictionary *originalDictionaryValue = [[super dictionaryValue] mutableCopy];
if (self.aPropertyThatShouldBeExcludedWhenNil == nil) {
[originalDictionaryValue removeObjectForKey:#"aPropertyThatShouldBeExcludedWhenNil"];
}
/* repeat the process for other "hidden" properties */
return originalDictionaryValue;
}
EDIT #2: Check out the code* for removing all values that are nil:
- (NSDictionary *)dictionaryValue {
NSMutableDictionary *modifiedDictionaryValue = [[super dictionaryValue] mutableCopy];
for (NSString *originalKey in [super dictionaryValue]) {
if ([self valueForKey:originalKey] == nil) {
[modifiedDictionaryValue removeObjectForKey:originalKey];
}
}
return [modifiedDictionaryValue copy];
}
* - code sample suggested by matths.

Answer 2

I remove nil valued keys by creating an MTLJSONAdapter subclass, and overriding -serializablePropertyKeys:forModel: method.
MTLJSONAdapterWithoutNil.h
/** A MTLJSONAdapter subclass that removes model dictionaryValue keys whose value is `[NSNull null]`. */
#interface MTLJSONAdapterWithoutNil : MTLJSONAdapter
#end
MTLJSONAdapterWithoutNil.m
#import "MTLJSONAdapterWithoutNil.h"
#implementation MTLJSONAdapterWithoutNil
- (NSSet *)serializablePropertyKeys:(NSSet *)propertyKeys forModel:(id<MTLJSONSerializing>)model {
NSMutableSet *ms = propertyKeys.mutableCopy;
NSDictionary *modelDictValue = [model dictionaryValue];
for (NSString *key in ms) {
id val = [modelDictValue valueForKey:key];
if ([[NSNull null] isEqual:val]) { // MTLModel -dictionaryValue nil value is represented by NSNull
[ms removeObject:key];
}
}
return [NSSet setWithSet:ms];
}
#end
And use this to create JSON dictionary instead. Like this:
NSDictionary *JSONDictionary = [MTLJSONAdapterWithoutNil JSONDictionaryFromModel:collection error:nil];
NOTE: if you are overriding NSValueTransformer methods for array or dictionary properties, you also have to change the MTLJSONAdapter class to your subclass as well. Like this:
+ (NSValueTransformer *)myDailyDataArrayJSONTransformer {
return [MTLJSONAdapterWithoutNil arrayTransformerWithModelClass:KBDailyData.class];
}

Answer 3

Overriding - dictionaryValues did not give me the expected behavior
So I created a method for MTL Base class
- (NSDictionary *)nonNullDictionaryWithAdditionalParams:(NSDictionary *)params error:(NSError *)error {
NSDictionary *allParams = [MTLJSONAdapter JSONDictionaryFromModel:self error: &error];
NSMutableDictionary *modifiedDictionaryValue = [allParams mutableCopy];
for (NSString *originalKey in allParams) {
if ([allParams objectForKey:originalKey] == NSNull.null) {
[modifiedDictionaryValue removeObjectForKey:originalKey];
}
}
[modifiedDictionaryValue addEntriesFromDictionary:params];
return [modifiedDictionaryValue copy];
}

Answer 4

The EDIT #2 used to work for me with the previous Mantle code base. Now I have to do the following to continue using EDIT #2:
In file MTLJSONAdapter.m, replace this line:
NSDictionary *dictionaryValue = [model.dictionaryValue dictionaryWithValuesForKeys:propertyKeysToSerialize.allObjects];
with
NSDictionary *dictionaryValue = model.dictionaryValue;
The above is my current workaround to get
{ }
instead of
{
"AddressLine2" : null,
"City" : null,
"ZipCode" : null,
"State" : null,
"AddressLine1" : null
}