通过指针解析排序查询

问题描述

我需要使用Parse进行简单的查询排序。

I need to do a simple query sort with Parse.

我有两个类： Captain 和船。每个船长都有一个 Boat 指针对象。

I have two classes: Captain and Boat. Every Captain has a Boat pointer object.

I列出表中包含其属性的所有 Captain 对象，例如名称， Boat name等。

I list all of the Captain objects in a table with their attributes, such as name, Boat name etc.

我需要能够通过船船长对象的查询进行排序c $ c>名称。我该怎么办？

I need to be able to sort the query of Captain objects, via the Boat name. How can I?

我可以使用 NSSortDescriptor 排序键（例如<$ c $）对直接属性进行排序c>船长 名称。但我需要按船的名称对船长对象进行排序$ c>。

I can sort a direct attribute with an NSSortDescriptor sort key such as the Captain name. But I need to sort the Captain objects by the name of their Boat.

推荐答案

如果您可以在排序限定符上使用点表示法，那会很好，例如：

It would be nice if you could use dot notation on the sort qualifiers, like:

[captainQuery orderByAscending:@"boat.name"];

不幸的是，属性点符号仅适用于includeKey：。所以这样做的方法是获取，包括相关对象，然后使用相关对象的属性进行本地排序：

Unfortunately the attribute dot notation applies only to includeKey:. So the way to do this to fetch, including the related object, then sort locally using the attribute of the related objects:

// ...
[captainQuery includeKey:@"boat"];
[query findObjectsInBackgroundWithBlock:^(NSArray *captains, NSError *error) {
    NSArray *sortedCaptains = [captains sortedArrayUsingComparator: ^(PFObject *capA, PFObject *capB) {
        return [capA[@"boat"][@"name"] compare:capB[@"boat"][@"name"]];
        // or reverse param order for descending
    }];
}];

编辑 - @Logan帮助指出此答案无法扩展好吧，如果您的查询页面通过成千上万的船长。如果船长数量巨大，最好包括一艘船 - >船长指针，并执行以下操作：

EDIT - @Logan helpfully points out that this answer doesn't scale well if your query pages through thousands of captains. If the captain count is huge, it might be better to include a boat->captain pointer and do the following:

更多环绕，你可以取船，订购ByAscending在他们的名字上，includeKey他们的船长（如果你的船有一个指向船长的后指针），然后在返回的（分类的）船上映射他们的船长。

More roundabout-ly, you could fetch boats, orderByAscending on their name, includeKey their captains (if your boats have a back-pointer to captain), and then map over the returned (sorted) boats for their captains.

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