如何使用PFQuery在iOS中获取表中的所有数据？

Question

我是iOS和的新手，我想从PFQuery中从Parse表中获取数据，就像

NSUInteger limit = 1500;
PFQuery *query = [PFQuery queryWithClassName:@"MapInfo"];
[query setLimit: limit];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error)
{
    if (!error) {
        NSLog(@"Successfully retrieved: %@", objects);
    } else {
        NSString *errorString = [[error userInfo] objectForKey:@"error"];
        NSLog(@"Error: %@", errorString);
    }
}];

它是我想要的工作，但它只给我1000个对象，我想在这里获取我的所有表数据，它包含到2000对象，它将与日俱增，请帮助我这一点。

现在，我编写了这样的代码，但它只给我1000个对象。

 NSMutableArray *allObjects = [NSMutableArray array];
NSUInteger limit = 0;
__block NSUInteger skip = 0;
PFQuery *query = [PFQuery queryWithClassName:@"MapInfo"];
[query setLimit: limit];
[query setSkip: skip];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
    if (!error) {
        [allObjects addObjectsFromArray:objects];
        if (objects.count == limit) {

            skip += limit;
            [query setSkip: skip];
            [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
                NSLog(@"Array %@",objects);
            }];
             }

             } else {
                 NSLog(@"Error: %@ %@", error, [error userInfo]);
             }
             }];

谢谢。

Answer 1

https://parse.com/questions/fetch-all-data-in-a-table-using-pfquery

可以使用“跳过和限制”参数对表中的所有对象进行分页，方法是添加要跳过的限制值，直到查询返回小于极限的对象数量。

NSMutableArray *allObjects = [NSMutableArray array];
NSUInteger limit = 0;
__block NSUInteger skip = 0;
PFQuery *query = [PFQuery queryWithClassName:@"MapInfo"];
[query setLimit: limit];
[query setSkip: skip];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
  if (!error) {
    // The find succeeded. Add the returned objects to allObjects
    [allObjects addObjectsFromArray:objects];
    if (objects.count == limit) {
      // There might be more objects in the table. Update the skip value and execute the query again.
      skip += limit;
      [query setSkip: skip];
      [query findObjects... // Execute the query until all objects have been returned. Keep adding the results to the allObjects mutable array.

    }
  } else {
    // Log details of the failure
    NSLog(@"Error: %@ %@", error, [error userInfo]);
  }
}];

Answer 2

我相信可以获取的对象数量有一个查询限制。我要做的是对同一件事进行两个查询，但是对于第二个查询，执行如下所示的操作

[query setSkip1000];

您可以跳过第一个查询中的前1000个对象，然后获取下一个1000个对象。使数组成为一个NSMutableArray，并在每个块内执行以下操作

[self.myArray addObjects:objects];，而不是self.myArray = objects;，这样就覆盖了数组中的对象。

编辑

而不是两个单独的查询，您也可以这样做

NSMutableArray *allObjectsArray = [NSMutableArray array];
//Set this to the amount of objects you want. Has to be be 1000 or less
NSUInteger limit = 0;

//Set this to the amount you want to skip (Usually 0)
NSUInteger skip = 0;
PFQuery *query = [PFQuery queryWithClassName:@"tempClass"];
[query setLimit: limit];
[query setSkip: skip];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
  if (!error) {
    // The find succeeded. Add the returned objects to allObjects
    [allObjectsArray addObjectsFromArray:objects];
    if (objects.count == limit) {
      // There could be more objects in your database. Update the skip number and perform the same query.
      skip = skip + limit;
      [query setSkip: skip];
      [query findObject...// Exactly the same way as you did before to get the rest of your objects in the database
    }

  } else {
    // Log details of the failure
    NSLog(@"Error: %@ %@", error, [error userInfo]);
  }
}];

Answer 3

这是一个简单的递归解决方案，可以使用块从类中检索所有对象。

这是你最初怎么称呼它的。

[self queryAllObjectswithLimit:1000 withSkip:0 withObjects:@[] withSuccess:^(NSArray * objects) {
    //All the objects
} failure:^(NSError * error) {
    //
}];

这是方法。

- (void)queryAllObjectswithLimit:(NSUInteger )limit withSkip:(NSUInteger )skip withObjects:(NSArray *)objects withSuccess:(void (^)(NSArray *objects))success failure:(void (^)(NSError *error))failure {
//Store all the Objects through each layer of recurrsion
NSMutableArray *allObjects = [NSMutableArray arrayWithArray:objects];
PFQuery *query = [PFQuery queryWithClassName:@"Class_Name"];
query.limit = limit;
query.skip = skip;
[query findObjectsInBackgroundWithBlock:^(NSArray * _Nullable objects, NSError * _Nullable error) {
    if (!error) {
        // The find succeeded. Add the returned objects to allObjects
        [allObjects addObjectsFromArray:objects];
        if (objects.count == limit) {
            //Recursively Call this until count does not equal limit, then begin returning all the objects back up
            [self queryAllObjectswithLimit:limit withSkip:skip+limit withObjects:allObjects withSuccess:^(NSArray * objects) {
                //This will return everything
                success(objects);
            } failure:^(NSError * error) {
                failure(error);
            }];
        } else {
            success(allObjects);
        }
    } else {
        failure(error);
    }
}];

}

我测试过少于1000个对象、1000个对象和1000多个对象，它运行得很好。

但是，要小心抓取多少对象，因为这会捕获所有对象，如果您正在处理大型数据集，这可能很快就会成为内存方面的一个问题。