CoreData database updates, data migration

When the General Program app is upgraded, the database may change, such as adding table fields, adding tables, etc. There are two things at this point:

The first is to simply delete the local old database directly, re-establish the new database, and the second is to migrate the database and update the database. The first case is a simple rough type, but does not retain any historical data and is generally not recommended for use. Here is the second case, divided into four steps: The first step, on the code, the main red font of the place

-(Nspersistentstorecoordinator *) persistentstorecoordinator

{

if (_persistentstorecoordinator! = nil) {

return _persistentstorecoordinator;

}

Nsfilemanager *filemanager = [Nsfilemanager Defaultmanager];

NSString *folderpath = [NSString stringwithformat:@ "%@/calendar", [Nssearchpathfordirectoriesindomains ( NSDocumentDirectory, Nsuserdomainmask, YES) Lastobject]];

if (![ FileManager Fileexistsatpath:folderpath]) {//If not present, this is the first time this program is run, then set up this folder

[FileManager Createdirectoryatpath:folderpath withintermediatedirectories:yes Attributes:nil Error:nil];

}

Nsurl *storeurl = [Nsurl fileurlwithpath:[folderpath stringbyappendingpathcomponent:@ "Calendar.sqlite"]];

nsdictionary *options = [nsdictionary dictionarywithobjectsandkeys:

[NSNumber Numberwithbool:yes],

Nsmigratepersistentstoresautomaticallyoption,

[NSNumber Numberwithbool:yes],

Nsinfermappingmodelautomaticallyoption, nil];

Nserror *error = nil;

_persistentstorecoordinator = [[Nspersistentstorecoordinator alloc] Initwithmanagedobjectmodel:[self Managedobjectmodel]];

if (![ _persistentstorecoordinatoraddpersistentstorewithtype:nssqlitestoretype configuration:nil URL:storeURL Options: options Error:&error]) {

NSLog (@ "unresolved error%@,%@", error, [error userInfo]);

Abort ();

}

return _persistentstorecoordinator;

}

Step Two: add a new version of the data model

Select Calendar.xcdatamodel File Click Editor, ADD model version to pop up a dialog box that fills in version Name (such as Calendar 2) and based on Model (such as Calen DAR).

Step three: Continue to select the Calendar.xcdatamodel file, press OPTION + COMMAND + 0 key to open the right side of Xcode, select Calendar 2 in the current of model version.

Fourth step: Modify your Calendar 2.xcdatamodel file (such as new fields, add tables, etc.), and then remember to update the entity code of your ALTER TABLE. (Note: This sequence of steps must be aware that you must not directly modify the table structure on the original Calendar.xcdatamodeld, and then add a new version, so that will always error)

Ps:nsurl *storeurl = [Nsurl fileurlwithpath:[folderpath stringbyappendingpathcomponent:@ "Calendar.sqlite"]]; This is still calendar.sqlite, not calendar 2.sqlite, as Calendar 2 has been selected in the third step.

OK, start the build.

CoreData database updates, data migration