Core Data is a framework that you use to manage the model layer objects in your application. It is also a persistent technology, in that it can persist the state of the model objects to disk but the important point is that Core Data is much more than just a framework to load and save data. Lazy loading of objects , and copy-on-write data sharing to reduce overhead. It is Sophisticated query compilation. Without writing SQL  queries, you can create complex queries by using an NSPredicate object with a fetch request.  

Core Data in iOS Objective- C 

Create new project  select empty project or single view application  or whatever your requirement  click on next button  display the following screen –

enter product name what you want in my case name is 'CoreDataSample' and check Use Core Data check box and click on next button. If you want to use  core data in existing project you can include  core data model using File->New->File open the following dialog click Next

after adding it to project select CoreDataSample.xcdatmodeld it look like the following screen-

you can add Entity on click on Add Entity (red marked)  .You can add attributes using + sign marked as blue and remove attributes using – sign marked as green. Now create your desired entity with their attributes. In AppDelegate.h  add the following lines if not in your appdelegate.h file  if you will create new project and select core data xcode will create it automatically in you AppDelegate.h file. My AppDelegate.h file is -

#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>
 
@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) NSManagedObjectContext
*managedObjectContext;
@property (strong, nonatomic) NSManagedObjectModel
*managedObjectModel;
@property (strong, nonatomic) NSPersistentStoreCoordinator
*persistentStoreCoordinator;
- (void)saveContext;
@end
 
AppDelegate.m  
 
#import "AppDelegate.h"
 
@implementation AppDelegate
 
 
- (BOOL)application:(UIApplication *)application
didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
   
    return YES;
}
 
- (void)applicationWillResignActive:(UIApplication *)application {
    // Sent when the application
is about to move from active to inactive state. This can occur for certain
types of temporary interruptions (such as an incoming phone call or SMS
message) or when the user quits the application and it begins the transition to
the background state.
    // Use this method to pause
ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games
should use this method to pause the game.
}
 
- (void)applicationDidEnterBackground:(UIApplication *)application {
    // Use this method to release
shared resources, save user data, invalidate timers, and store enough
application state information to restore your application to its current state
in case it is terminated later.
    // If your application
supports background execution, this method is called instead of
applicationWillTerminate: when the user quits.
}
 
- (void)applicationWillEnterForeground:(UIApplication *)application {
    // Called as part of the
transition from the background to the inactive state; here you can undo many of
the changes made on entering the background.
}
 
- (void)applicationDidBecomeActive:(UIApplication *)application {
    // Restart any tasks that
were paused (or not yet started) while the application was inactive. If the
application was previously in the background, optionally refresh the user
interface.
}
 
- (void)applicationWillTerminate:(UIApplication *)application {
    // Called when the
application is about to terminate. Save data if appropriate. See also
applicationDidEnterBackground:.
    // Saves changes in the
application's managed object context before the application terminates.
    [self saveContext];
}
 
 
#pragma mark -
Core Data stack
 
@synthesize
managedObjectContext = _managedObjectContext;
@synthesize
managedObjectModel = _managedObjectModel;
@synthesize
persistentStoreCoordinator = _persistentStoreCoordinator;
 
- (NSURL
*)applicationDocumentsDirectory {
    // The directory the
application uses to store the Core Data store file. This code uses a directory
named "com.mindstick.CoreDataSample" in the application's documents
directory.
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}
 
- (NSManagedObjectModel
*)managedObjectModel {
    // The managed object model for
the application. It is a fatal error for the application not to be able to find
and load its model.
    if (_managedObjectModel != nil) {
        return _managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"CoreDataSample" withExtension:@"momd"];
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return _managedObjectModel;
}
 
- (NSPersistentStoreCoordinator
*)persistentStoreCoordinator {
    // The persistent store
coordinator for the application. This implementation creates and returns a
coordinator, having added the store for the application to it.
    if (_persistentStoreCoordinator != nil) {
        return _persistentStoreCoordinator;
    }
    
    // Create the coordinator and
store
    
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"CoreDataSample.sqlite"];
    NSError *error = nil;
    NSString *failureReason =
@"There was an error creating or loading the application's
saved data.";
    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
        // Report any
error we got.
        NSMutableDictionary *dict = [NSMutableDictionary dictionary];
        dict[NSLocalizedDescriptionKey] = @"Failed
to initialize the application's saved data";
        dict[NSLocalizedFailureReasonErrorKey] =
failureReason;
        dict[NSUnderlyingErrorKey] = error;
        error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:9999 userInfo:dict];
        // Replace this
with code to handle the error appropriately.
        // abort()
causes the application to generate a crash log and terminate. You should not
use this function in a shipping application, although it may be useful during
development.
        NSLog(@"Unresolved
error %@, %@", error, [error userInfo]);
        abort();
    }
    
    return _persistentStoreCoordinator;
}
 
 
- (NSManagedObjectContext
*)managedObjectContext {
    // Returns the managed object
context for the application (which is already bound to the persistent store
coordinator for the application.)
    if (_managedObjectContext != nil) {
        return _managedObjectContext;
    }
    
    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (!coordinator) {
        return nil;
    }
    _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
    [_managedObjectContext setPersistentStoreCoordinator:coordinator];
    return _managedObjectContext;
}
 
#pragma mark -
Core Data Saving support
 
- (void)saveContext {
    NSManagedObjectContext
*managedObjectContext = self.managedObjectContext;
    if
(managedObjectContext != nil) {
        NSError *error = nil;
        if
([managedObjectContext hasChanges] &&
![managedObjectContext save:&error]) {
            // Replace this
implementation with code to handle the error appropriately.
            // abort()
causes the application to generate a crash log and terminate. You should not
use this function in a shipping application, although it may be useful during
development.
            NSLog(@"Unresolved
error %@, %@", error, [error userInfo]);
            abort();
        }
    }
}
 
@end

Now create another UIViewController add employee as shown in the screen shot- add three textfield named as Name,Email Id,Contact Number .

Add button on navigation bar search and Add New and create IBAction for buttons and IBOutlet for textfields. My DetailViewController.h and  DetailViewController.m code is -

//
//  DetailViewController.h
//  CoreDataSample
 
#import <UIKit/UIKit.h>
#include "AppDelegate.h"
#import <CoreData/CoreData.h>
@interface
DetailViewController : UIViewController
 
@property (strong, nonatomic) id detailItem;
@property (weak, nonatomic) IBOutlet UITextField *txtName;
@property (weak, nonatomic) IBOutlet UITextField *txtEmail;
@property (weak, nonatomic) IBOutlet UITextField *txtContactNo;
@property(weak,nonatomic)AppDelegate *appDelegate;
- (IBAction)AddPerson:(id)sender;
 
@end
 
 
//
//  DetailViewController.m
//  CoreDataSample
//
 
 
#import "DetailViewController.h"
#import "Employee+CoreDataProperties.h"
 
@interface DetailViewController ()
 
@end
 
@implementation
DetailViewController
 
#pragma mark -
Managing the detail item
 
- (void)setDetailItem:(id)newDetailItem {
    if (_detailItem !=
newDetailItem) {
        _detailItem = newDetailItem;
            
        // Update the
view.
        
    }
}
 
 
 
- (void)viewDidLoad {
    [super viewDidLoad];
      _appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    // Do any additional setup
after loading the view, typically from a nib.
 
    
    
}
 
- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources
that can be recreated.
}
 
- (IBAction)AddPerson:(id)sender {
  
    Employee* item = [NSEntityDescription insertNewObjectForEntityForName:@"Employee"
                                               inManagedObjectContext:_appDelegate.managedObjectContext];
    item.name=_txtName.text;
    item.email = _txtEmail.text;
    item.contactNo = _txtContactNo.text;
    [_appDelegate saveContext];
    _txtName.text=@"";
    _txtEmail.text=@"";
    _txtContactNo.text=@"";
}
 
@end

Now you can add employee info using core data .Let us display saved data in my table view controller . Create UITableViewController  with a prototype cell with identifier Cell and create a segue from  DetailViewController to EmployeeTableViewController  for Search button on navigation bar. I am attaching screen shot of Employee view in UITableView-

Here is source code of  my  EmployeeTableView.h and EmployeeTableView.m   code is as-

//
//  EmployeeTableView.h
//  CoreDataSample
//
 
 
#import <UIKit/UIKit.h>
#import "AppDelegate.h"
#import "Employee.h"
 
@interface
EmployeeTableView : UITableViewController
@property (weak, nonatomic) IBOutlet UITableViewCell *ReuseCell;
@property (retain,nonatomic) NSFetchedResultsController *
fetchedResultsController;
@property (retain,nonatomic) NSMutableArray *
employeeCollection;
@property(retain,nonatomic)AppDelegate *appDelegate;
@end
 
 
//
//  EmployeeTableView.m
//  CoreDataSample
 
#import "EmployeeTableView.h"
 
@implementation
EmployeeTableView
@synthesize fetchedResultsController;
@synthesize
employeeCollection;
- (void)viewDidLoad {
    [super viewDidLoad];
    self.tableView.delegate=self;
    self.tableView.dataSource=self;
     _appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
   
    NSFetchRequest *fetchRequest =
[[NSFetchRequest alloc] initWithEntityName:@"Employee"];
    self.employeeCollection = [[_appDelegate.managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
    NSLog(@"count=%ld", (unsigned long)self.employeeCollection.count);
   // [self.tableView
reloadData];
    
}
 
#pragma mark -
Table View
 
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}
 
- (NSInteger)tableView:(UITableView *)tableView
numberOfRowsInSection:(NSInteger)section {
    return self.employeeCollection.count;
}
 
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *CellIdentifier
= @"Cell";
    UITableViewCell *cell = [tableView
dequeueReusableCellWithIdentifier:CellIdentifier];
    if (!cell)
    {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle
                                      reuseIdentifier:@"Cell"];
        
    }
    Employee  *item = [self.employeeCollection objectAtIndex:indexPath.row];
    [cell.textLabel setText:item.name];
    [cell.detailTextLabel setText:item.contactNo];
    
    return cell;
}
 
- (BOOL)tableView:(UITableView *)tableView
canEditRowAtIndexPath:(NSIndexPath *)indexPath {
    // Return NO if you do not
want the specified item to be editable.
    return YES;
}
 
- (void)tableView:(UITableView *)tableView
commitEditingStyle:(UITableViewCellEditingStyle)editingStyle
forRowAtIndexPath:(NSIndexPath *)indexPath {
    if (editingStyle ==
UITableViewCellEditingStyleDelete) {
        [_appDelegate.managedObjectContext deleteObject:[self.employeeCollection objectAtIndex:indexPath.row]];
        [self.employeeCollection removeObjectAtIndex:indexPath.row];
        [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
       
    } else if (editingStyle ==
UITableViewCellEditingStyleInsert) {
        // Create a new
instance of the appropriate class, insert it into the array, and add a new row
to the table view.
    }
}
 
-(void)viewWillDisappear:(BOOL)animated{
    [super
viewWillDisappear:YES];
     [_appDelegate saveContext];
}
@end

Note- Do not forget to create NSManagedObject Subclass.Select your CoreDataSample.xcdatamodeld and go to Editer-> Create  NSManagedObject Subclass. 

and following is the Employee class code -

//  Employee+CoreDataProperties.h
//  CoreDataSample
//
//
//  Choose "Create NSManagedObject
Subclass…" from the Core Data editor menu
//  to delete and recreate this implementation
file for your updated model.
//
 
#import "Employee.h"
 
NS_ASSUME_NONNULL_BEGIN
 
@interface Employee
(CoreDataProperties)
 
@property (nonatomic) int64_t id;
@property (nullable, nonatomic, retain) NSString *name;
@property (nullable, nonatomic, retain) NSString *email;
@property (nullable, nonatomic, retain) NSString *contactNo;
@property (nonatomic) NSTimeInterval creationDate;
@property (nonatomic) NSTimeInterval
modificationDate;
 
@end
 
NS_ASSUME_NONNULL_END
 
 
//
//  Employee+CoreDataProperties.m
//  CoreDataSample
//
//  Choose "Create NSManagedObject Subclass…" from the Core Data editor menu
//  to delete and recreate this implementation file for your updated model.
//
 
#import "Employee+CoreDataProperties.h"
 
@implementation Employee (CoreDataProperties)
 
@dynamicid;
@dynamic name;
@dynamic email;
@dynamic contactNo;
@dynamic creationDate;
@dynamic modificationDate;
 
@end
 
 //
//  Employee.h
//  CoreDataSample
//
//
 
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
 
NS_ASSUME_NONNULL_BEGIN
 
@interface Employee : NSManagedObject
 
// Insert code here to declare functionality of your managed object subclass
 
@end
 
NS_ASSUME_NONNULL_END
 
#import "Employee+CoreDataProperties.h"
 
 
 
//
//  Employee.m
//  CoreDataSample
//
 
#import "Employee.h"
 
@implementation Employee
 
// Insert code here to add functionality to your managed object subclass
 
@end