ios - Automatically Generated Primary Key -

i developing ios app.using core data storing data.but primary keys automatically generated.data can stored id.

//code  nsmanagedobjectcontext *context = [self managedobjectcontext];     nsmanagedobject *userobj = [nsentitydescription insertnewobjectforentityforname:@"detailsave" inmanagedobjectcontext:context];      [userobj setvalue:[nsnumber numberwithinteger:_userobj.userid] forkey:@"id"];     [userobj setvalue:_titlelabel.text forkey:@"title"];     nsinteger valint = 1;     nsnumber *val = [nsnumber numberwithinteger:valint];     [userobj setvalue:val forkey:@"quantity"];      nsstring *maxpurch = [dict objectforkey:@"_max_purchases_per_user"];     nsnumber *maxval = [nsnumber numberwithinteger:[maxpurch integervalue]];     [userobj setvalue:maxval forkey:@"max_purch"];      nsstring *maxpurch = [dict objectforkey:@"_max_purchases"];     nsnumber *max = [nsnumber numberwithinteger:[maxpurch integervalue]];     [userobj setvalue:max forkey:@"available"];      nsstring *baseprice = [dict objectforkey:@"_base_price"];     nsnumber *baseprice = [nsnumber numberwithinteger:[baseprice integervalue]];     [userobj setvalue:baseprice forkey:@"amount"];      //nslog(@"%@",userobj);        nslog(@"app dir: %@",[[[nsfilemanager defaultmanager] urlsfordirectory:nsdocumentdirectory indomains:nsuserdomainmask] lastobject]);      nserror *error = nil;     if (![context save:&error]) {         nslog(@"can't save! %@ %@", error, [error localizeddescription]);     }      nsfetchrequest *request = [[nsfetchrequest alloc] init];       // count entity     [request setentity:[nsentitydescription entityforname:@"detailsave" inmanagedobjectcontext:context]];     [request setincludessubentities:no];     nserror *err;     nsuinteger count = [context countforfetchrequest:request error:&err];     if(count == nsnotfound) {      } 

if m=8, or if m close 8 (e.g. 9 or 10), takes while , can more clever.

-(nsmutablearray *)geteightrandomlessthan:(int)m {   nsmutablearray *listofnumbers = [[nsmutablearray alloc] init];   (int i=0 ; i<m ; ++i) {     [listofnumbers addobject:[nsnumber numberwithint:i]]; // add 1 numbers between 1 , m rather 0 , m-1   }   nsmutablearray *uniquenumbers = [[[nsmutablearray alloc] init] autorelease];   int r;   while ([uniquenumbers count] < 8) {     r = arc4random() % [listofnumbers count];     if (![uniquenumbers containsobject:[listofnumbers objectatindex:r]]) {       [uniquenumbers addobject:[listofnumbers objectatindex:r]];     }   }   [listofnumbers release];   return uniquenumbers; } 

or

unsigned int permuteqpr(unsigned int x) {     static const unsigned int prime = 4294967291;     if (x >= prime)         return x;  // 5 integers out of range mapped themselves.     unsigned int residue = ((unsigned long long) x * x) % prime;     return (x <= prime / 2) ? residue : prime - residue; }