How to convert JSON to Object - iphone

Question

I defined some custom classes, such as Teacher, Student...
Now I receive teacher info (JSON string) from remote server.
How can I convert the JSON string to Teacher object.
In Java, it's easy to implement a common method for all class (Teacher, Student...) with reflect.
But in Objective-C on iOS, the best way I can find is to use Entity of Core Data, which has setValue:forKey method. First I convert the JSON string to NSDictionary, the set the key-value pair in the disctionary to the Entry.
Is there any better ways?
(I'm from China, so maybe my English is poor, sorry!)

Answer 1

First, do you use JSON Parser? (if not, i'd recommend using SBJson).
Second, why not create an initWithDictionary init method in your custom class that returns self object?

Answer 2

These are all good frameworks for JSON parsing to dictionaries or other primitives, but if you're looking to avoid doing a lot of repetitive work, check out http://restkit.org . Specifically, check out https://github.com/RestKit/RestKit/blob/master/Docs/Object%20Mapping.md This is the example on Object mapping where you define mapping for your Teacher class and the json is automagically converted to a Teacher object by using KVC. If you use RestKit's network calls, the process is all transparent and simple, but I already had my network calls in place and what I needed was to convert my json response text to a User object (Teacher in your case) and I finally figured out how. If that's what you need, post a comment and I'll share how to do it with RestKit.
Note: I will assume the json is output using the mapped convention {"teacher": { "id" : 45, "name" : "Teacher McTeacher"}}. If it's not this way, but instead like this {"id" : 45, "name" : "Teacher McTeacher"} then don't worry ... object mapping design doc in the link shows you how to do this...a few extra steps, but not too bad.
This is my callback from ASIHTTPRequest
- (void)requestFinished:(ASIHTTPRequest *)request {
id<RKParser> parser = [[RKParserRegistry sharedRegistry] parserForMIMEType:[request.responseHeaders valueForKey:#"Content-Type"]]; // i'm assuming your response Content-Type is application/json
NSError *error;
NSDictionary *parsedData = [parser objectFromString:apiResponse error:&error];
if (parsedData == nil) {
NSLog(#"ERROR parsing api response with RestKit...%#", error);
return;
}
[RKObjectMapping addDefaultDateFormatterForString:#"yyyy-MM-dd'T'HH:mm:ssZ" inTimeZone:[NSTimeZone timeZoneWithAbbreviation:#"UTC"]]; // This is handy in case you return dates with different formats that aren't understood by the date parser
RKObjectMappingProvider *provider = [RKObjectMappingProvider new];
// This is the error mapping provider that RestKit understands natively (I copied this verbatim from the RestKit internals ... so just go with it
// This also shows how to map without blocks
RKObjectMapping* errorMapping = [RKObjectMapping mappingForClass:[RKErrorMessage class]];
[errorMapping mapKeyPath:#"" toAttribute:#"errorMessage"];
[provider setMapping:errorMapping forKeyPath:#"error"];
[provider setMapping:errorMapping forKeyPath:#"errors"];
// This shows you how to map with blocks
RKObjectMapping *teacherMapping = [RKObjectMapping mappingForClass:[Teacher class] block:^(RKObjectMapping *mapping) {
[mapping mapKeyPath:#"id" toAttribute:#"objectId"];
[mapping mapKeyPath:#"name" toAttribute:#"name"];
}];
[provider setMapping:teacherMapping forKeyPath:#"teacher"];
RKObjectMapper *mapper = [RKObjectMapper mapperWithObject:parsedData mappingProvider:provider];
Teacher *teacher = nil;
RKObjectMappingResult *mappingResult = [mapper performMapping];
teacher = [mappingResult asObject];
NSLog(#"Teacher is %# with id %lld and name %#", teacher, teacher.objectId, teacher.name);
}
You can obviously refactor this to make it cleaner, but that now solves all my problems.. no more parsing... just response -> magic -> Object

Answer 3

Specifically, check out https://github.com/fanpyi/jsontooc/blob/master/README.md
This is the example convert JSON data to Objective-C model, use nodejs.