POST JSON data into existing object

Question

I am retrieving JSON data from a URL that is formatted like so:

{"zoneresponse":
{"tasks":
 [{"datafield1":"datafor1", 
   "datafield2":"datafor2", 
   "datafield3":"datafor3",...
 }]
}}

I have no control over the structure as it is from a private API.

How do I insert data in a selected data field of an existing object?

I have tried this:

self.responseData = [NSMutableData data];

//testingURL is the api address to the specific object in tasks
NSURL *url = [NSURL URLWithString:testingURL];

NSMutableDictionary *params = [[NSMutableDictionary alloc] init];
[[[params objectForKey:@"zoneresponse"] objectForKey:@"tasks"] setValue:@"HelloWorld" forKey:@"datafield1"];
//HAVE TRIED setObject: @"" objectForKey: @"" as well

//*****PARAMS IS EMPTY WHEN PRINTED IN NSLog WHICH IS PART OF THE ISSUE - SETTING VALUE DOES NOT WORK

NSError * error = nil;

NSLog(@"Params is %@", params);

NSData *requestdata = [NSJSONSerialization dataWithJSONObject:params options:0 error:&error];

NSMutableURLRequest *request;
request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:@"POST"];
[request setValue:[NSString stringWithFormat:@"%d", [requestdata length]] forHTTPHeaderField:@"Content-Length"];
[request setValue:@"application/json" forHTTPHeaderField:@"Accept"];
[request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
[request setHTTPBody:requestdata];

NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:request delegate:self];


if(conn) {
    NSLog(@"Connection Successful, connection is: %@", conn);

} else {
    NSLog(@"Connection could not be made");
}

The connection is being made but the dictionary params is empty when printed (the setValue is not displaying) and is not entering any data into the field I select.

I have checked these links but nothing explains whether it will insert into the right field and implies it will create a new object rather than update the existing one.

How to update data on server db through json api?

How to send json data in the Http request using NSURLRequest

Delegate methods

//any time a piece of data is received we will append it to the responseData object
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [self.responseData appendData:data];

    NSError *jsonError;

    id responseDict =
    [NSJSONSerialization JSONObjectWithData:self.responseData
                                options:NSJSONReadingAllowFragments
                                  error:&jsonError];

    NSLog(@"Did Receive data %@", responseDict);
}

 //if there is some sort of error, you can print the error or put in some other handling here, possibly even try again but you will risk an infinite loop then unless you impose some sort of limit
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    // Clear the activeDownload property to allow later attempts
    self.responseData = nil;

    NSLog(@"Did NOT receive data ");

}

//connection has finished, the requestData object should contain the entirety of the response at this point
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSError *jsonError;
    id responseDict =
    [NSJSONSerialization JSONObjectWithData:self.responseData
                                options:NSJSONReadingAllowFragments
                                  error:&jsonError];
    if(responseDict)
    {
        NSLog(@"%@", responseDict);
    }
    else
    {
        NSLog(@"%@", [jsonError description]);
    }

    //clear out our response buffer for future requests
    self.responseData = nil;
}

The first method here states that data was received with "Did Receive data (null)", there is no error with connection however the final method prints the error message "JSON text did not start with array or object and option to allow fragments not set.", which is understandable because there is no data or object being sent.

How do I insert data into a selected field of an existing object?

Answer 1

You do this wrong:

NSMutableDictionary *params = [[NSMutableDictionary alloc] init];
[[[params objectForKey:@"zoneresponse"] objectForKey:@"tasks"] setValue:@"HelloWorld" forKey:@"datafield1"];

Your params is empty dictionary and no object will be returned with [params objectForKey:@"zoneresponse"].

Try this:

NSMutableDictionary *params = [NSMutableDictionary new];
params[@"zoneresponse"] = @{@"tasks": @{@"datafield1": @"HelloWorld"}};

This will work but object for key @"tasks" will be immutable. To add another objects to tasks dictionary we need to make it mutable:

NSMutableDictionary *params = [NSMutableDictionary new];
NSMutableDictionary *tasks = [NSMutableDictionary new];
params[@"zoneresponse"] = @{@"tasks": tasks};
params[@"zoneresponse"][@"tasks"][@"datafield1"] = @"HelloWorld";

or

NSMutableDictionary *params = [NSMutableDictionary new];    
params[@"zoneresponse"] = @{@"tasks": [@{@"datafield1": @"HelloWorld"} mutableCopy]};

Then you can add another objects to tasks:

params[@"zoneresponse"][@"tasks"][@"datafield2"] = @"HelloWorld2";
params[@"zoneresponse"][@"tasks"][@"datafield3"] = @"HelloWorld3";

I think my answer will bring some clarity to operations with dictionaries for you.