从核心数据数据库检索数据的替代方法-iOS [英] Alternate way to retrieve data from core data database - ios

问题描述

从数据库检索数据时遇到性能问题.

I am having performance issues while retrieving data from the database.

现在，这就是我的方法.

Right now, this is how I do it.

+(NSMutableArray *) searchObjectsInContext: (NSString*) entityName : (NSPredicate *) predicate : (NSString*) sortKey : (BOOL) sortAscending 

{
     i3EAppDelegate *appDelegate = (i3EAppDelegate *)[[UIApplication sharedApplication] delegate];
     NSManagedObjectContext *context = [appDelegate managedObjectContext];

     NSFetchRequest *request = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:context];
     [request setEntity:entity];     
     [request setFetchBatchSize:5];
    //[request setFetchLimit:10];
     [request setReturnsObjectsAsFaults:NO];

     // If a predicate was passed, pass it to the query
     if(predicate != nil)
     {
          [request setPredicate:predicate];
     }

     // If a sort key was passed, use it for sorting.
     if(sortKey != nil)
     {
          NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:sortKey ascending:sortAscending];
          NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
          [request setSortDescriptors:sortDescriptors];
               [sortDescriptors release];
          [sortDescriptor release];
     }

     NSError *error;
     NSMutableArray *mutableFetchResults = [[context executeFetchRequest:request error:&error] mutableCopy];

     if (mutableFetchResults == nil) {

          // Handle the error.

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

          exit(-1);  // Fail
          }

     [request release];
     //[context release];
     appDelegate = nil;

     return [mutableFetchResults autorelease];

}

是否还有其他方法可以执行相同的操作，但是速度更快?

Is there any other way to perform the same operation but in a faster way?

如果是这样，那么如果有人可以帮助我，那就太好了.

If so, it would be great if someone could help me out in this.

推荐答案

有几个问题:

1. 您没有谓词.因此，您正在检索整个表.这可能是您最大的问题.
2. 您将在检索时加载所有完整对象.这将大大减慢速度.如果您不需要实现所有对象，则建议重新打开 -setReturnsObjectsAsFaults:.
3. -setFetchBatchSize:的设置可能没有达到您期望的效果.如果要限制返回的结果数，请使用 -setFetchLimit:
4. 对 NSArray 结果进行 -mutableCopy 没有价值.我怀疑您是从书中得到的，建议您停止这样做.

1. You do not have a predicate. Therefore you are retrieving the entire table. That is probably your single biggest issue.
2. You are loading all of the full objects on retrieval. This is going to slow things down considerably. If you do not need the entire objects realized then I would suggest turning -setReturnsObjectsAsFaults: back on.
3. The setting of -setFetchBatchSize: is probably not having the effect you are expecting. If you want to limit the number of results returned use -setFetchLimit:
4. Making a -mutableCopy of the NSArray results has no value. I suspect you got that from a book and recommend you stop doing it.

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