CoreData additions and deletions and data migration examples

As a manager, the most basic function is to delete and change the search.

1. Insert

 appdelegate *app = [[uiapplication sharedapplication] delegate  ]; Nsmanagedobjectcontext  *context = [app Managedobjectcontext]; Nsmanagedobject *newmanagedobject  = [nsentitydescription insertnewobjectforentityforname:@ " entityname  "   Inmanagedobjectcontext:context]; [Newmanagedobject setvalue:value Forkey:  @ " propertyname   "  *error;  if  (! [Context Save:&error]) { //  Handle the error ... } 

2. Enquiry

Nsfetchrequest *fetchrequest =[[Nsfetchrequest alloc] init]; Nsmanagedobjectcontext*managedobjectcontext =Appdelegate.managedobjectcontext; Nsentitydescription*entity = [Nsentitydescription entityforname:@"Hero"Inmanagedobjectcontext:managedobjectcontext]; Nssortdescriptor*sortdescriptor1 =[[Nssortdescriptor alloc]initwithkey:@ "name" Ascending:yes]; Nssortdescriptor*sortdescriptor2 =[[Nssortdescriptor alloc]initwithkey:@ "secretidentity" ascending:yes]; Nsarray*sortdescriptors =[[Nsarray Alloc]initwithobjects:sortdescriptor1, SortDescriptor2, nil]; [Fetchrequest setsortdescriptors:sortdescriptors]; [Fetchrequest setentity:entity]; [Fetchrequest setfetchbatchsize: -]; Nsarray*objecs = [Context executefetchrequest:fetchrequest error:&error];if (Objets==nil | | error = NIL) {
Do the processing}

3. Modification

-(void) Applicationwillresignactive: (Nsnotification *) notification{NSLog (@"applicationwillresignactive"); //creating a Managed object ContextNsmanagedobjectcontext *context =[Appdelegate Managedobjectcontext]; Nsfetchrequest*request =[[Nsfetchrequest alloc]init]; Nsentitydescription*entitydescription = [Nsentitydescription entityforname:@"User"Inmanagedobjectcontext:context];        [Request Setentity:entitydescription]; Nsmanagedobject*user =Nil; Nserror*error; Nsarray*objets = [Context executefetchrequest:request error:&ERROR]; if(objets==Nil) {NSLog (@"there has a error!"); //do error handling    }     if([Objets count]>0){        //not the first time, update the dataNSLog (@"Update Action"); User= [Objets Objectatindex:0]; }Else{NSLog (@"Insert Operation"); //save for the first time, insert new datauser = [Nsentitydescription insertnewobjectforentityforname:@"User"Inmanagedobjectcontext:context]; } [user SetValue:self.serverIp.text Forkeypath:@"ServerIP"]; [User SetValue:self.userName.text Forkeypath:@"UserName"]; [Context Save:&error];}

4. Delete

Nsmanagedobjectcontext *managedobjectcontext =*if (![ Context save:&Error]) {    %@,%@ ", error, [error userInfo]);    Exit (-1//  Fail}

5. Data Migration

When the program changes, in many simple cases, CoreData provides a lightweight automatic data migration, such as the following three scenarios can be achieved by turning on the CoreData automatic migration:
1. Simply add a field
2. Change a required field to an optional field
3. Change the optional fields to required fields (but be sure to define default values)

CoreData additions and deletions and data migration examples