ExecuteFetchRequest返回空值

Question

我的插入数据的代码如下（它从服务器接收json数据，解析它并插入它）

- (void)connectionDidFinishLoading:(NSURLConnection *)connection  {
[myButton setTitle:@"Get o/p from file" forState:UIControlStateNormal];
JsonStorage *event = (JsonStorage *)[NSEntityDescription insertNewObjectForEntityForName:@"JsonStorage" inManagedObjectContext:managedObjectContext];
NSDictionary *json=[NSJSONSerialization JSONObjectWithData:mutabledata options:NSJSONReadingMutableContainers error:nil];

NSDictionary *message=[json objectForKey:@"message"];
NSMutableString *stringtemp=[[NSMutableString alloc] init];
//[temp appendString:@"Message: \n"];
for(id key in message)
{
    [stringtemp appendString:[[NSString alloc] initWithFormat:@"%@ is %@ \n",key,message[key]]];

}
[event setMessage1:[[NSString alloc] initWithString:stringtemp]];
[event setApplicationid:[[NSString alloc] initWithFormat:@"application id is %@",json[@"applicationid"]]];
[event setRankings:[[NSString alloc] initWithFormat:@"Rankings for %@",json[@"rankings"]]];

NSArray *array=[json objectForKey:@"ranks"];
NSMutableString *temp=[[NSMutableString alloc] init];
for(int i=0;i<[array count];i++)
{   
    NSDictionary *rank=array[i];


    [temp appendString:[[NSString alloc] initWithFormat: @"username is %@\n",rank[@"user_name"]] ];

    [temp appendString:[[NSString alloc] initWithFormat: @"email id is %@\n",rank[@"user_email"]] ];
    int inc=i+1;

    [temp appendString:[[NSString alloc] initWithFormat: @"%@",rank[[[NSString alloc] initWithFormat:@"%d",inc ]]] ];

    [temp appendString:[[NSString alloc] initWithFormat: @"\n"]];


}

[event setRankdetails:temp];
NSLog(@"asdasfafew %@",[event rankdetails]);
NSError *error;
if (![managedObjectContext save:&error]) {
    // This is a serious error saying the record could not be saved.
    // Advise the user to restart the application
    NSLog(@"error");
}

[eventArray insertObject:event atIndex:0];
   secondlabel.text=[NSString stringWithFormat:@" Date received, It is stored in the core data\n " ];
 }

正确插入值，然后我的刷新视图函数（从核心数据中获取数据）如下所示

 - (void) RefreshView
 {

NSEntityDescription *entity = [NSEntityDescription entityForName:@"JsonStorage" inManagedObjectContext:managedObjectContext];

// Setup the fetch request
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];


// Fetch the records and handle an error
NSError *error;
NSMutableArray *mutableFetchResults;
[mutableFetchResults removeAllObjects];
mutableFetchResults= [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];

if (!mutableFetchResults) {
    NSLog(@"too big error");
    // Handle the error.
    // This is a serious error and should advise the user to restart the application
}
 // Save our fetched data to an array
[self setEventArray: mutableFetchResults];

NSMutableString *temp2=[[NSMutableString alloc] init];
//temp2=nil;
for (NSManagedObject *info in eventArray) {
          //  NSLog(@"reached refreshview");

   NSString *temp=[[NSString alloc] initWithFormat:@"%@",[info valueForKey:@"message1"]];
    //NSLog(@"Value is %@",temp);

    [temp2 appendString:temp];
   // [temp2 appendString:@"\n"];
    //NSLog(@"reached refreshview1");
    NSString *temp3=[[NSString alloc] initWithFormat:@"%@",[info valueForKey:@"applicationid"]];

    [temp2 appendString:temp3];

   // [temp2 appendString:@"\n"];

    //NSLog(@"reached refreshview2");
    NSString *temp4=[[NSString alloc] initWithFormat:@"%@",[info valueForKey:@"rankings"]];

    [temp2 appendString:temp4];

   // [temp2 appendString:@"\n"];

    //NSLog(@"reached refreshview3");
    NSString *temp5=[[NSString alloc] initWithFormat:@"%@",[info valueForKey:@"rankdetails"]];

    [temp2 appendString:temp5];

}
//NSLog(@"final temp is %@",temp2);

NSString *finalstring=[temp2 stringByReplacingOccurrencesOfString:@"(null)" withString:@""];
//NSLog(@"final string is is %@",finalstring);
secondlabel.text=finalstring;


}

temp2保持打印（null）（null）.... 提前致谢