Question

I am learning the core data
How to delete and update the data using core data. I have worked on upload and fetch. I need to write the methods for delete and update. Please tell me how to update and delete a recode using core data.

Below I have written code for upload and fetch data from table using core data.

-(void)uploadData
{
    Employee *empObj=(Employee *)[NSEntityDescription insertNewObjectForEntityForName:@"Employee" inManagedObjectContext:self.managedObjectContext];


    empObj.empId=[NSNumber numberWithInt:12345];
    empObj.empSalary=[NSNumber numberWithInt:25000];

    empObj.empName=@"Venu";
    empObj.empDesignation=@"Programmer";
    empObj.empExp=@"2 Years";

    if ([self.managedObjectContext hasChanges] )
    {
        [self.managedObjectContext save:nil];
    }

}
-(void)fetchData
{
    NSEntityDescription *empEntity = [NSEntityDescription entityForName:@"Employee" inManagedObjectContext:self.managedObjectContext];

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

    NSArray *fatherArray=[self.managedObjectContext executeFetchRequest:request error:nil];

    [request setEntity:empEntity];

    NSArray *empArray=[self.managedObjectContext executeFetchRequest:request error:nil];

    for (int i=0; i<[empArray count]; i++) 
    {
        printf("\n=================================Recored== %d==================================== ",i);

        Employee *empObj=[empArray objectAtIndex:i];
        printf("\n obj.empName========= %s",[empObj.empName UTF8String]);
        printf("\n obj.empDesignation========= %s",[empObj.empDesignation UTF8String]);
        printf("\n obj.empExp========= %s",[empObj.empExp UTF8String]);
        printf("\n obj.empId========= %d",[empObj.empId intValue]);
        printf("\n obj.empSalary========= %d",[empObj.empSalary intValue]);
        printf("\n============================================================================= ");

    }
}

Answer 1

I am doing a project which involved in Core Data, and I would
like to share something with you about it.

It is a clear that before you delete or update a record you need
to retrieve that record.

Use the employee with empId 12345 as an example,

a)Delete

NSFetchRequest *request = [[NSFetchRequest alloc] init];  
NSEntityDescription *entity = [NSEntityDescription entityForName:@:@"Employee"                                                
                                          inManagedObjectContext:self.managedObjectContext];
[request setEntity:entity];   


NSPredicate *pred = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"empId = %d", 12345]];  
[request setPredicate:pred];


NSArray *empArray=[self.managedObjectContext executeFetchRequest:request error:nil];  
[request release];

if ([empArray count] > 0){
    Employee *employee = [empArray objectAtIndex:0];
    [self.managedObjectContext deleteObject:employee];
    [self.managedObjectContext save:nil];
}

b) update

NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@:@"Employee"    
                                          inManagedObjectContext:self.managedObjectContext];
[request setEntity:entity];   

NSPredicate *pred = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"empId = %d", 12345]];
[request setPredicate:pred];

NSArray *empArray=[self.managedObjectContext executeFetchRequest:request error:nil];
[request release];

if ([empArray count] > 0){
    Employee *employee = [empArray objectAtIndex:0];

    employee.empSalary=[NSNumber numberWithInt:45000];

    employee.empName=@"John";
    employee.empDesignation=@"Analysist";
    employee.empExp=@"4 Years";

    [self.managedObjectContext save:nil];
}