Why is my Realm object not saving stored values?

问题:

I was browsing around looking for a solution to implement a small offline data storage in one of my apps which would be easy and quick to use. Anyways, I came across with Realm to do this. But, I'm getting a problem that everytime I launch my app the content in the database is null.

I do all the allocation and call the beginWriteTransaction method. Set my database variable value. Then, I add the object to realm and finally commitWriteTransaction.

So, I do an NSLog to see if the value is actually set properly which it is(after updating it within my app). But when I shut down my application or stopped and run it again in the xcode iphone5 simulator. I try to set in the viewDidLoad method the value from database to a global variable in my app. Which I perform a NSLog to check if the value is either in my database or the global variable but it's display as null, meaning that is not getting store/saved.

This is the code..

@interface iReceiptDataBase : RLMObject  @property NSString* receiptNo;  @end  RLM_ARRAY_TYPE(iReceiptDataBase)  @implementation iReceiptDataBase  @end  //******** View Controller Implementation ************  - (void)viewDidLoad {      self.realm = [RLMRealm defaultRealm]; // property type RLMRealm     [realm beginWriteTransaction];      self.myDataBase = [[iReceiptDataBase alloc] init]; // property type iReceiptDataBase     receiptNumber = [myDataBase.receiptNo intValue];      NSLog(@"In my realm database(first call) -> %@", myDataBase.receiptNo);      NSLog(@"In my local app(first call) -> %d", receiptNumber);  }  -(void)drawPDF:(NSString*)fName {      receiptNumber += 1; // property type int      myDataBase.receiptNo = [NSString stringWithFormat:@"%d", receiptNumber];      NSLog(@"In my realm database(second call) -> %@", myDataBase.receiptNo);  }  - (void)viewWillDisappear:(BOOL)animated {      [realm addObject:myDataBase];      [realm commitWriteTransaction];  }

I will also take in consideration any other options to achieve this.. Thanks!

*****UPDATE!** This is what I get in my test, which I changed to do beginWriteTransaction and commitWriteTransaction in both methods, but still doesn't work. It gets the value that I provide within my app but when I access again it doesn't pull/fetch that value from the database if it was ever store..

回答1:

The problem with your realm object is that you are not querying realm for your object. Rather, you are only allocating a new iReciptDataBase object. You will first need to add a property to that object so that you will be able to query for it, something like databaseId shown here:

@interface iReceiptDatabase : RLMObject @property NSString *receiptNo; @property NSString *databaseId; @end  @implementation iReceiptDatabase @end  RLM_ARRAY_TYPE(iReceiptDatabase)

Then in your viewDidLoad, you first query the realm file for an existing object, then only after not finding it, you would allocate it:

- (void)viewDidLoad {     [super viewDidLoad];      RLMRealm *realm = [RLMRealm defaultRealm];     iReceiptDatabase *myDatabase = [[iReceiptDatabase objectsWhere:@"databaseId = '1'"] firstObject];      if(!myDatabase) {         [realm beginWriteTransaction];         myDatabase = [[iReceiptDatabase alloc] init];         myDatabase.receiptNo = @"1";         myDatabase.databaseId = @"1";         [realm addObject:myDatabase];         [realm commitWriteTransaction];     }      //... }

回答2:

My guess would be viewWillDisappear is never being called. I would recommend committing your write transaction after each change to your data rather than leaving the transaction open as long as the view is visible - instead of adding the object at the end, you could change your other methods to commit the data:

- (void)viewDidLoad {      self.realm = [RLMRealm defaultRealm]; // property type RLMRealm      [realm beginWriteTransaction];     self.myDataBase = [[iReceiptDataBase alloc] init]; // property type iReceiptDataBase     [realm addObject:myDataBase];     [realm commitWriteTransaction];      receiptNumber = [myDataBase.receiptNo intValue];      NSLog(@"In my realm database(first call) -> %@", myDataBase.receiptNo);     NSLog(@"In my local app(first call) -> %d", receiptNumber); }  -(void)drawPDF:(NSString*)fName {      receiptNumber += 1; // property type int      [realm beginWriteTransaction];     myDataBase.receiptNo = [NSString stringWithFormat:@"%d", receiptNumber];     [realm commitWriteTransaction];      NSLog(@"In my realm database(second call) -> %@", myDataBase.receiptNo); }

I would also consider storing receiptNo as an int on your data model.

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