CODEWITHSUNDEEP
objectcore-dataexists
user1688130
user1688130

Reputation: 11

How can I check whether a NSManagedObject already exist in coredata by my primary key?

I use this method,but not correct.

- (BOOL)checkExistByEntityName:(NSString *)entityName primaryKeyName:(NSString *)keyName primaryKey:(NSNumber *)primaryKey
{
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:managedObjectContext];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%@==%@", keyName, primaryKey];

    [request setEntity:entity];
    [request setPredicate:predicate];

    NSError *error = nil;
    NSInteger count = [managedObjectContext countForFetchRequest:request error:&error];

    [request release];

     if (count > 0) {
          return YES;
    } else {
          return NO;
    }
}

Upvotes: 1

Views: 625

Answers (1)

Lorenzo B
Lorenzo B

Reputation: 33428

Predicate programming guide is your friend.

The format string supports printf-style format arguments such as %x (see “Formatting String Objects”). Two important arguments are %@ and %K.

  • %@ is a var arg substitution for an object value—often a string, number, or date.
  • %K is a var arg substitution for a key path. When string variables are substituted into a format string using %@ , they are surrounded by quotation marks. If you want to specify a dynamic property name, use %K in the format string, as shown in the following example.
NSString *attributeName = @"firstName";
NSString *attributeValue = @"Adam";
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%K like %@",
        attributeName, attributeValue];

So, just use

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%K == %@", keyName, primaryKey];

Hope that helps.

Upvotes: 1

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