ios - Fetch arrays of values in CoreData -

in xcode project, have 2 entities coredata. these entities called session , sessiondetails. session has 1 attribute called timecompleted (type: date) time stamp of event. session in one-to-many relationship sessiondetails attribute important averagedistance (type: float).

the sessions sorted using timecompleted. fetch averagedistance values of sorted sessions , place them in array used generate plot. x-axis have date of event , y-axis have averagedistance value. not concerned right creating plot rather extracting values used it. appreciate help!

you can use key-value coding array of attribute values. assuming averagedistance attribute of session, can following:

nsarray *sessions = ...; // sorted array of session objects nsarray *distvalues = [sessions valueforkey:@"averagedistance"]; 

distvalues array of nsnumber objects containing averagedistance each session object.

update: turned out in discussion, there to-many relationship session sessiondetails, averagedistance attribute of sessiondetails, , need possible (timecompleted, averagedistance) pairs, sorted timecompleted.

therefore, should fetch sessiondetails objects instead of fetching session objects, , sort them according timecompleted of related session:

nsfetchrequest *request = [nsfetchrequest fetchrequestwithentityname:@"sessiondetails"]; nssortdescriptor *sort = [nssortdescriptor sortdescriptorwithkey:@"session.timecompleted" ascending:yes]; [request setsortdescriptors:@[sort]]; nsarray *result = [context executefetchrequest:request error:&error]; 

(i have assumed have inverse relationship session sessiondetails session.)

now can extract timecompleted , averagedistance value these objects, using key-value coding:

nsarray *xvalues = [result valueforkeypath:@"session.timecompleted"]; nsarray *yvalues = [result valueforkey:@"averagedistance"];