Core Data Quickest way to delete all instances of an entity

Question

I m using Core Data to locally persist results from a Web Services call  The web service returns the full object model for  let s say   Cars  - could be about 2000 of them  and I can t make the Web Service return anything less than 1 or ALL cars   The next time I open my application  I want to refresh the Core Data persisted copy by calling the Web Service for all Cars again  however to prevent duplicates I would need to purge all data in the local cache first   Is there a quicker way to purge ALL instances of a specific entity in the managed object context  e g  all entities of type  CAR    or do I need to query them call  then iterate through the results to delete each  then save   Ideally I could just say delete all where entity is Blah

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func deleteAll entityName  String         let fetchRequest   NSFetchRequest lt NSFetchRequestResult gt  entityName  entityName      let deleteRequest   NSBatchDeleteRequest fetchRequest  fetchRequest      deleteRequest resultType    resultTypeObjectIDs     guard let context   self container  viewContext         else   print  error in deleteAll               return        do           let result   try context execute deleteRequest  as  NSBatchDeleteResult         let objectIDArray   result  result as   NSManagedObjectID          let changes   AnyHashable   Any     NSDeletedObjectsKey   objectIDArray as Any          NSManagedObjectContext mergeChanges fromRemoteContextSave  changes  into   context         catch           print error localizedDescription

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A good answer was already posted  this is only a recommendation   A good way would be to just add a category to NSManagedObject and implement a method like I did   Header File  e g  NSManagedObject Ext h    interface NSManagedObject  Logic      void  deleteAllFromEntity  NSString   entityName    end     Code File   e g  NSManagedObject Ext m    implementation NSManagedObject  Logic      void  deleteAllFromEntity  NSString   entityName       NSManagedObjectContext  managedObjectContext    AppDelegate managedObjectContext       NSFetchRequest   allRecords     NSFetchRequest alloc  init        allRecords setEntity  NSEntityDescription entityForName entityName inManagedObjectContext managedObjectContext         allRecords setIncludesPropertyValues NO       NSError   error   nil      NSArray   result    managedObjectContext executeFetchRequest allRecords error  amp error       for  NSManagedObject   profile in result             managedObjectContext deleteObject profile             NSError  saveError   nil       managedObjectContext save  amp saveError       end       the only thing you have to is to get the managedObjectContext from the app delegate  or where every you have it in     afterwards you can use it like    NSManagedObject deleteAllFromEntity   EntityName      one further optimization could be that you remove the parameter for tha entityname and get the name instead from the clazzname  this would lead to the usage    ClazzName deleteAllFromEntity       a more clean impl  as category to NSManagedObjectContext     implementation NSManagedObjectContext  Logic   -  void  deleteAllFromEntity  NSString   entityName       NSFetchRequest   allRecords     NSFetchRequest alloc  init        allRecords setEntity  NSEntityDescription entityForName entityName inManagedObjectContext self         allRecords setIncludesPropertyValues NO       NSError   error   nil      NSArray   result    self executeFetchRequest allRecords error  amp error       for  NSManagedObject   profile in result             self deleteObject profile             NSError  saveError   nil       self save  amp saveError       end   The usage then    managedObjectContext deleteAllFromEntity   EntityName

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In Swift 3 0   func deleteAllRecords               delete all data         let context   appDelegate persistentContainer viewContext          let deleteFetch   NSFetchRequest lt NSFetchRequestResult gt  entityName   YourClassName           let deleteRequest   NSBatchDeleteRequest fetchRequest  deleteFetch           do               try context execute deleteRequest              try context save             catch               print   There was an error

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iOS 9 0 and Later   NSBatchDeleteRequest is used to delete records in core data  It works very fast and takes less time to delete all records from an entity  It requires NSFetchRequest in argument  If you want to delete all records from an entity  you can use it and it works for me  let manageObject NSManagedObjectContext   appDelegateObject managedObjectContext  let fetchRequest   NSFetchRequest entityName     EnityName      let deleteRequest   NSBatchDeleteRequest fetchRequest  fetchRequest   let persistCor NSPersistentStoreCoordinator   appDelegateObject persistentObject  do           try persistCor executeRequest deleteRequest  withContext  manageObject          try manageObject save         catch           print error  localizedDescription

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if the entity contains a lot of entries the best way is like this because it saves memory      -  void deleteAll  NSManagedObjectContext   managedObjectContext entityName  NSString   entityName       NSFetchRequest  fetchRequest     NSFetchRequest alloc  init        managedObjectContext setUndoManager nil       NSEntityDescription  entity    NSEntityDescription entityForName entityName inManagedObjectContext managedObjectContext        fetchRequest setEntity entity        fetchRequest setIncludesPropertyValues NO        fetchRequest setFetchLimit 100      you can change this number if you want     NSError  error      NSArray  items    managedObjectContext executeFetchRequest fetchRequest error  amp error       while   items count   gt  0             autoreleasepool               for  NSManagedObject  item in items                     managedObjectContext deleteObject item                             if    managedObjectContext save  amp error                     NSLog   Error deleting    - error     self entityName  error                                   items    managedObjectContext executeFetchRequest fetchRequest error  amp error

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quick purge of all objects in DB   func purgeAllData         let uniqueNames   persistentContainer managedObjectModel entities compactMap    0 name         uniqueNames forEach    name  in       let fetchRequest   NSFetchRequest lt NSFetchRequestResult gt  entityName  name         let batchDeleteRequest   NSBatchDeleteRequest fetchRequest  fetchRequest           do           try persistentContainer viewContext execute batchDeleteRequest          catch           let nserror   error as NSError         fatalError  Unresolved error   nserror     nserror userInfo

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the OOP way without any strings as entities names Swift 3   Xcode 10   func batchDelete lt T gt  in context  NSManagedObjectContext  fetchRequest  NSFetchRequest lt T gt   throws       guard let request   fetchRequest as  NSFetchRequest lt NSFetchRequestResult gt  else           throw ErrorService defaultError           let batchDeleteRequest   NSBatchDeleteRequest fetchRequest  request      do           try context execute batchDeleteRequest        catch           throw error           then just call in do catch block      let fetchRequest  NSFetchRequest lt YourEntity gt    YourEntity fetchRequest       do           let data   try context fetch fetchRequest          if data count  gt  0               try self batchDelete in  context  fetchRequest  fetchRequest                  catch              throw error

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iOS 10 and later  Works with all versions  Pass entity name and iterate through to delete all the entries and save the context   func deleteData entityToFetch  String  completion   escaping   returned  Bool  - gt               let context   NSManagedObjectContext           context   your managedObjectContext          let fetchRequest   NSFetchRequest lt NSFetchRequestResult gt            fetchRequest entity   NSEntityDescription entity forEntityName  entityToFetch  in  context          fetchRequest includesPropertyValues   false          do                  let results   try context fetch fetchRequest  as   NSManagedObject              for result in results                   context delete result                            try context save               completion true            catch               completion false              print  fetch error -  error localizedDescription

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The above answers give a good insight on how to delete the  quot Cars quot  However  I want this answer to challenge the approach itself  1- SQLite CoreData is a relational database  In this case  where there isn t any releation  I would advise against using CoreData and maybe using the file system instead  or keep things in memory  2- In other examples  where  quot Car quot  entity have other relations  and therefore CoreData  I would advise against having 2000 cars as root entity  Instead I would give them a parent  let s say  quot CarsRepository quot  entity  Then you can give a one-to-many relationship to the  quot Car quot  entity  and just replace the relationship to point to the new cars when they are downloaded  Adding the right deletion rule to the relationships ensures the integrity of the model

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A little bit more cleaned and universal   Add this method    -  void deleteAllEntities  NSString   nameEntity       NSFetchRequest  fetchRequest     NSFetchRequest alloc  initWithEntityName nameEntity        fetchRequest setIncludesPropertyValues NO     only fetch the managedObjectID      NSError  error      NSArray  fetchedObjects    theContext executeFetchRequest fetchRequest error  amp error       for  NSManagedObject  object in fetchedObjects                 theContext deleteObject object              error   nil       theContext save  amp error

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Swift 4  iOS 10  Static function which can apply for any entity to remove all of its data  protocol NSManagedObjectHelper     extension NSManagedObject  NSManagedObjectHelper     extension NSManagedObjectHelper where Self  NSManagedObject       static func removeAllObjectsInContext   managedContext  NSManagedObjectContext            let request  NSFetchRequest   NSFetchRequest entityName  String describing  self           let deleteRequest   NSBatchDeleteRequest fetchRequest  request          do               deleteRequest resultType    resultTypeObjectIDs  to clear objects from memory             let result   try managedContext execute deleteRequest  as  NSBatchDeleteResult             if let objectIDArray   result  result as   NSManagedObjectID                    let changes    NSDeletedObjectsKey   objectIDArray                    By calling mergeChangesFromRemoteContextSave  all of the NSManagedObjectContext instances that are referenced will be notified that the list of entities referenced with the NSManagedObjectID array have been deleted and that the objects in memory are stale  This causes the referenced NSManagedObjectContext instances to remove any objects in memory that are loaded which match the NSManagedObjectID instances in the array                    NSManagedObjectContext mergeChanges fromRemoteContextSave  changes  into   managedContext                             try managedContext save             catch let error               print error                       Room  is an entity  Room removeAllObjectsInContext self persistentContainer viewContext    Edited on 20191025  the  Self fetchRequest    instruction may cause issue if we use multiple target in same projects  So replaced with NSFetchRequest entityName  String describing  self

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Swift   let fetchRequest   NSFetchRequest   fetchRequest entity   NSEntityDescription entityForName entityName  inManagedObjectContext  context  fetchRequest includesPropertyValues   false  var error NSError  if let results   context executeFetchRequest fetchRequest  error   amp error  as   NSManagedObject        for result in results           context deleteObject result             var error NSError      if context save  amp error               do something after save        else if let error   error           println error userInfo           else if let error   error       println  error    error

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This code will work for both iOS 9 and below  class func deleteAllRecords in entity   String     entity   Your Entity Name                let context   CoreDataStack getContext      Note - Replace your context here with CoreDataStack getContext           let deleteFetch   NSFetchRequest lt NSFetchRequestResult gt  entityName  entity          if  available iOS 9                           let deleteRequest   NSBatchDeleteRequest fetchRequest  deleteFetch              do                               try context execute deleteRequest                  try context save                             catch                               print  There was an error   error                                    else                       do                  let deleteRequest   try context fetch deleteFetch                  for anItem in deleteRequest                       context delete anItem as  NSManagedObject                                              catch                               print  There was an error   error                                    CoreDataStack saveContext      Note - Replace your savecontext here with CoreDataStack saveContext

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Reset Entity in Swift 3     func resetAllRecords in entity   String     entity   Your Entity Name                let context     UIApplication shared delegate as  AppDelegate   persistentContainer viewContext         let deleteFetch   NSFetchRequest lt NSFetchRequestResult gt  entityName  entity          let deleteRequest   NSBatchDeleteRequest fetchRequest  deleteFetch          do                       try context execute deleteRequest              try context save                     catch                       print   There was an error

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Swift 3 X and Swift 4 X   Easy way  Change only YourTable      let fetchRequest   NSFetchRequest lt NSFetchRequestResult gt  entityName   YourTable       fetchRequest returnsObjectsAsFaults   false      do               let results   try context fetch fetchRequest          for managedObject in results                       let managedObjectData NSManagedObject   managedObject as  NSManagedObject             context delete managedObjectData                  catch let error as NSError           print  Detele all my data in   entity  error     error    error userInfo

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Extending Dave Delong s answer   Swift Version that takes care of iOS 9 and previous versions as well  I have also covered Error handling in this   let appDelegate  AppDelegate   UIApplication sharedApplication   delegate as  AppDelegate      let fetchRequest   NSFetchRequest entityName   Car       if  available iOS 9 0               let delete   NSBatchDeleteRequest fetchRequest  fetchRequest          do               try appDelegate persistentStoreCoordinator executeRequest delete  withContext  appDelegate managedObjectContext            catch let error as NSError               print  Error occured while deleting    error                    else              Fallback on earlier versions         let carRequest   NSFetchRequest           carRequest entity   NSEntityDescription entityForName  Cars   inManagedObjectContext  appDelegate managedObjectContext          carRequest includesPropertyValues   false          do               let cars  NSArray   try appDelegate managedObjectContext executeFetchRequest carRequest               for car in cars                   appDelegate managedObjectContext delete car                             try appDelegate managedObjectContext save              catch let error as NSError               print  Error occured while fetching or saving    error

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In Swift 2 0   func deleteAllData entity  String        let appDelegate   UIApplication sharedApplication   delegate as  AppDelegate     let managedContext   appDelegate managedObjectContext     let fetchRequest   NSFetchRequest entityName  entity      fetchRequest returnsObjectsAsFaults   false      do                let results   try managedContext executeFetchRequest fetchRequest          for managedObject in results                       let managedObjectData NSManagedObject   managedObject as  NSManagedObject             managedContext deleteObject managedObjectData                  catch let error as NSError           print  Detele all data in   entity  error     error    error userInfo

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iOS 9 and later   iOS 9 added a new class called NSBatchDeleteRequest that allows you to easily delete objects matching a predicate without having to load them all in to memory  Here s how you d use it   Swift 5  let fetchRequest  NSFetchRequest lt NSFetchRequestResult gt    NSFetchRequest entityName   Car   let deleteRequest   NSBatchDeleteRequest fetchRequest  fetchRequest   do       try myPersistentStoreCoordinator execute deleteRequest  with  myContext    catch let error as NSError          TODO  handle the error     Objective-C  NSFetchRequest  request     NSFetchRequest alloc  initWithEntityName   Car    NSBatchDeleteRequest  delete     NSBatchDeleteRequest alloc  initWithFetchRequest request    NSError  deleteError   nil   myPersistentStoreCoordinator executeRequest delete withContext myContext error  amp deleteError     More information about batch deletions can be found in the  What s New in Core Data  session from WWDC 2015  starting at  14 10    iOS 8 and earlier   Fetch  em all and delete  em all   NSFetchRequest  allCars     NSFetchRequest alloc  init    allCars setEntity  NSEntityDescription entityForName   Car  inManagedObjectContext myContext     allCars setIncludesPropertyValues NO     only fetch the managedObjectID  NSError  error   nil  NSArray  cars    myContext executeFetchRequest allCars error  amp error    allCars release     error handling goes here for  NSManagedObject  car in cars       myContext deleteObject car     NSError  saveError   nil   myContext save  amp saveError     more error handling here

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Swift 4  iOS 12 and Xcode 10 Update  100  working just cut  amp  paste  Just put this function in relevant class and call this function self deleteData   in viewDidLoad   or anywhere or under a function or a button so that by clicking a button all the data from entity should be deleted  and replace the  myEntity  as your entity that you have defined in your core data  func deleteData         let appDel AppDelegate    UIApplication shared delegate as  AppDelegate      let context NSManagedObjectContext   appDel persistentContainer viewContext     let fetchRequest   NSFetchRequest lt NSFetchRequestResult gt  entityName   myEntity       fetchRequest returnsObjectsAsFaults   false              do           let results   try context fetch fetchRequest          for managedObject in results               if let managedObjectData  NSManagedObject   managedObject as  NSManagedObject                   context delete managedObjectData                                catch let error as NSError           print  Deleted all my data in myEntity error     error    error userInfo

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Use NSBatchDeleteRequest to delete multiple records If Minimum iOS is 9 0  If background thread  execute NSManagedObjectContext save else use NSFetchRequest to get records and delete all records in for loop and Save once deletion done

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Swift 3 solution with iOS 9  NSBatchDeleteRequest  and fallback to earlier iOS versions implemented as an extension on  NSManagedObjectContext   Apple reference https   developer apple com library content featuredarticles CoreData Batch Guide BatchDeletes BatchDeletes html  extension NSManagedObjectContext       func batchDeleteEntities lt T  NSManagedObject gt  ofType type  T Type  throws           let fetchRequest   NSFetchRequest lt NSFetchRequestResult gt  entityName  String describing  type self           if  available iOS 9 0                   let request   NSBatchDeleteRequest fetchRequest  fetchRequest              let result   try execute request  as  NSBatchDeleteResult             if let objectIDArray   result  result as   NSManagedObjectID                    let changes    NSDeletedObjectsKey  objectIDArray                  NSManagedObjectContext mergeChanges fromRemoteContextSave  changes  into   self                           else               fetchRequest includesPropertyValues   false             let results   try fetch fetchRequest              if let actualResults   results as   NSManagedObject    actualResults isEmpty                   actualResults forEach   delete  0

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in iOS 11 3 and Swift 4 1  let fetchRequest   NSFetchRequest lt NSFetchRequestResult gt  entityName  entityName          let batchDeleteRequest   NSBatchDeleteRequest fetchRequest  fetchRequest           batchDeleteRequest resultType    resultTypeCount         do               let batchDeleteResult   try dataController viewContext execute batchDeleteRequest  as  NSBatchDeleteResult             print  The batch delete request has deleted   batchDeleteResult result   records                dataController viewContext reset      reset managed object context  need it for working            catch               let updateError   error as NSError             print    updateError     updateError userInfo                you have to call reset after you do execute  If not  it will not update on the table view

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This is a similar question to the one here and someone suggested setting up a relationship delete rule so you only have to delete one object  So if you have or can make an entity with a to-many relationship to the cars and set the delete rule to cascade when you delete the higher entity all the cars will be deleted as well  This may save some processing time since you don t have to do the steps involved with loading ALL the cars  In a larger data set this could be absolutely necessary

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Why not fold in the data that you receive with the existing cache  Otherwise it s not really  refreshing   it s  starting again  and you might as well drop delete the SQLLite file and start again  assuming you re not persisting other data as well

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Dave Delongs s Swift 2 0 answer was crashing for me  in iOS 9   But this worked   let fetchRequest   NSFetchRequest entityName   Car   let deleteRequest   NSBatchDeleteRequest fetchRequest  fetchRequest       do           try managedObjectContext executeRequest deleteRequest          try managedObjectContext save             catch let error as NSError             Handle error

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For Swift 2 0   class func clearCoreData entity String      let fetchRequest   NSFetchRequest     fetchRequest entity   NSEntityDescription entityForName entity  inManagedObjectContext  moc     fetchRequest includesPropertyValues   false   do       if let results   try moc  executeFetchRequest fetchRequest  as   NSManagedObject          for result in results           moc  deleteObject result                 try moc  save             catch       LOG debug  failed to clear core data

[ios] Core Data: Quickest way to delete all instances of an entity

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