The code in this article is from: http://www.appcoda.com/introduction-to-core-data/
Students who want to learn Core Data do not miss:) Here are some of the frequently used code snippets for my personal records.
There is a entity:device with three properties: Company, name, version.
1. Get the Context method:
-(Nsmanagedobjectcontext *) managedobjectcontext { Nsmanagedobjectcontext *context = nil; ID delegate = [[UIApplication sharedapplication] delegate]; if ([Delegate performselector: @selector (managedobjectcontext)]) { context = [delegate managedobjectcontext]; } return context;}
2. Add a piece of data:
Nsmanagedobjectcontext *context = [self managedobjectcontext]; Create a new Managed object nsmanagedobject *newdevice = [Nsentitydescription insertnewobjectforentityforname:@ " Device "Inmanagedobjectcontext:context"; [Newdevice setValue:self.nameTextField.text forkey:@ "name"]; [Newdevice setValue:self.versionTextField.text forkey:@ "version"]; [Newdevice setValue:self.companyTextField.text forkey:@ "Company"]; Nserror *error = nil; Save the object to persistent store if (![ Context Save:&error]) { NSLog (@ "Can ' t save!%@%@", error, [error localizeddescription]); }
3. Delete a single piece of data:
Nsmanagedobjectcontext *context = [self managedobjectcontext];//Delete object from Database[context deleteobject:[ Self.devices ObjectAtIndex:indexPath.row]]; Nserror *error = nil;if (![ Context Save:&error]) { NSLog (@ "Can ' t delete!%@%@", error, [error localizeddescription]); return;}
4. Modify a piece of data:
Nsmanagedobjectcontext *context = [self managedobjectcontext]; Update existing Device[self.device setValue:self.nameTextField.text forkey:@ "name"]; [Self.device setValue:self.versionTextField.text forkey:@ "version"]; [Self.device setValue:self.companyTextField.text forkey:@ "Company"]; Nserror *error = nil;//Save The object to persistent Storeif (![ Context Save:&error]) { NSLog (@ "Can ' t save!%@%@", error, [error localizeddescription]);}
5. Query a bunch of data:
Fetch the devices from persistent data storensmanagedobjectcontext *managedobjectcontext = [self managedobjectcontext] ; Nsfetchrequest *fetchrequest = [[Nsfetchrequest alloc] initwithentityname:@ "Device"];self.devices = [[ Managedobjectcontext executefetchrequest:fetchrequest Error:nil] mutablecopy];
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