ios - Core Data Migration: Could not cast value of type 'NSManagedObject_MyType' to 'MyModule.MyType' -


i'm doing 'medium-weight' core data migration. i'm using mapping model migrate 1 legacy store / data model different store , different model (i.e. different .xcdatamodeld) files, , using custom nsentitymigrationpolicy objects applicable.

where had sorts of objects unrelated on object graph, want have master object library enable me wipe out of associated data (using cascade delete rule).

i've run problems during migration because of custom method in nsentitymigrationpolicy subclass:

class legacytomodernpolicy: nsentitymigrationpolicy {  func libraryformanager(_ manager: nsmigrationmanager) -> library {      let fetchrequest: nsfetchrequest<library> = nsfetchrequest(entityname: library.entity().name!)      fetchrequest.predicate = nil     fetchrequest.sortdescriptors = [nssortdescriptor(key: "filename", ascending: true)]     fetchrequest.fetchlimit = 1      {         // fail here if nsfetchrequest<library>         let results = try manager.destinationcontext.fetch(fetchrequest)           log.info("results: \(results)")          if results.count == 1 {             // can fail here if nsfetchrequest<nsmanagedobject>             return results.first! as! library           } else {             let newlib = library(context: manager.destinationcontext)             return newlib         }      } catch {         log.error("error fetching: \(error.localizeddescription)")     }      let newlib = library(context: manager.destinationcontext)     return newlib   } }

an exception thrown, , error message is:

could not cast value of type 'nsmanagedobject_library_' (0x6100000504d0) 'songbooksimple.library' (0x101679180).

the question is, why happening, , matter? because migration happening, perhaps it's enough return nsmanagedobject correct entity description ?

the reason during migration, should not using instances of nsmanagedobject subclasses. need express of these in form of nsmanagedobject. code above must become:

class legacytomodernpolicy: nsentitymigrationpolicy {  static func find(entityname: string,                  in context: nsmanagedobjectcontext,                  sortdescriptors: [nssortdescriptor],                  predicate: nspredicate? = nil,                  limit: int? = nil) throws -> [nsmanagedobject] {      let fetchrequest: nsfetchrequest<nsmanagedobject> = nsfetchrequest(entityname: entityname)     fetchrequest.predicate = predicate     fetchrequest.sortdescriptors = sortdescriptors     if let limit = limit {         fetchrequest.fetchlimit = limit     }      {         let results = try context.fetch(fetchrequest)         return results     } catch {         log.error("error fetching: \(error.localizeddescription)")         throw error     } }  func libraryformanager(_ manager: nsmigrationmanager) -> nsmanagedobject {      {         var library: nsmanagedobject? = try legacytomodernpolicy.find(entityname: library.entity().name!,                                                 in: manager.destinationcontext,                                                 sortdescriptors: [nssortdescriptor(key: "filename", ascending: true)],                                                 with: nil,                                                 limit: 1).first         if library == nil {             let dinstance = nsentitydescription.insertnewobject(forentityname: library.entity().name!, into: manager.destinationcontext)              // awakefrominsert not called, have things did there, here:             dinstance.setvalue(library.libraryfilename, forkey: #keypath(library.filename))             dinstance.setvalue(nsdate(timeintervalsince1970: 0), forkey: #keypath(library.updatedat))             library = dinstance         }          return library!      } catch {         fatalerror("not sure why failing!")     } }}

you can read more less-than-fun experiences core data migrations here.


Comments

Post a Comment

Popular posts from this blog

angular - Ionic slides - dynamically add slides before and after -

hi i'm using ngfor create set of 3 slides while starting in middle i'm guaranteed able slide left or right on start. when slide right can simple listen reachedend , push slide array i'm looping. but have problem adding slide beginning. if same above , use e.g. array.unshift() or spread add item beginning, view think it's on position 0 , snaps view new slide. the code below work animates slide change index 1. slide = [0,1,2] //example loop slidechanged(event) { if(this.slides.isbeginning()){ this.slide = [this.slide[0]-1, ...this.slide]; this.slides.update(); this.slides.slideto(1) } } <ion-slides [initialslide]="1" (ionslidedidchange)="slidechanged($event)"> <ion-slide *ngfor="let item of slide"> <h1>slide {{item}}</h1> </ion-slide> </ion-slides> any appreciated! you can using ionslidenextend , ionslideprevend events slides . please...
Read more

Add a dynamic header in angular 2 http provider -

i have http interceptor built via tutorial https://scotch.io/@kashyapmukkamala/using-http-interceptor-with-angular2 the problem need have dynamic header changes automatically once changes 'mode' in app. service able tell interceptor change header, or have interceptor pull header (which string)from service each request. able throwing away patch method, call http.patch('new header string') set header string. call in service controls 'mode' setting. wondering if there way interceptor pull recent value service each request or if can add method http provider via interceptor? i've tried call service in interceptor each request returns undefined. because creating new instance of service or copying value before service fired , loaded/changed data. i don't want pass header string every http provider call because defeats purpose of having interceptor, id able set once changes or have provider fetch service before makes request. tl;dr : need add autom...
Read more

minify - Minimizing css files -

i want know how css files can minimized. currently, using external sites css minifier compress css files. however, after removing whitespaces, comments, etc, file sizes reduced 10-15%. how frameworks bootstrap manage make minimized versions kilobytes. as example, css is: body { background-color: #ff0; } the reduction goes 28 bytes 22 bytes other css files have lot more characters still smaller this. actually minifying code means it's remove thing code white space characters new line characters comments block delimiters it reduces amount of code has transferred on web , speed site load fastly.but unreadable format.
Read more