解析:当我只有PFUser时，如何使用PFRelation查询? [英] Parse: How do I query using PFRelation when I just have PFUser?
问题描述
这是我要做的事的一个例子.我有当前用户为PFUser，在另一个名为Item的类上，我有一个名为所有者"的关系，它是PFUser的关系.我想查询在关系中具有当前用户的所有Item实例.
Here is an example of what I am trying to do. I have the current user as PFUser and on another class named Item I have a relation named "owners" which is a relation of PFUser. I want to query for all instances of Item which have the current user in the relation.
我看到了相反查询方式的示例，但是我没有看到如何获取关系，然后将其过滤为关系上的PFUser匹配项.这是一个例子.
I see examples of the opposite way of querying, but I do not see how to get a relation and then filter it to a PFUser match on the relation. Here is one example.
https://www.parse.com/questions/inverse-relationship-support
PFObject老师= ...////老师"类的PFObject PFRelation studentsRelation = [教师关系forKey:@"students"]; PFQuery * query = studentsRelation.query; [查询findObjectsInBackground:...
PFObject teacher = ... // PFObject of class "Teacher" PFRelation studentsRelation = [teacher relationforKey:@"students"]; PFQuery *query = studentsRelation.query; [query findObjectsInBackground:...
对于我的示例，我会这样做...
For my example I would do this...
PFObject item = [PFObject objectWithClassName:@"Item"];
PFRelation relation = [parseObject relationforKey:@"owner"]; // Filter to PFUser?
[query findObjectsInBackground:...
我可以使用whereKey，但是我应该使用什么呢?我可以在objectId上匹配吗?
I can use whereKey, but what do I use? Do I match on objectId?
[query whereKey:@"objectId" equalTo:user.objectId];
我不断收到错误102:RelatedTo运算符需要一个有效的指针.我的猜测是，由于我是从一个空对象开始的，所以没有起点.使用Teacher的示例必须从填充的实例开始.我唯一填充的是PFUser.必须有一种方法来查询Item实例，并根据它与当前用户所拥有的所有者"关系对其进行过滤.我无法弄清楚，也没有找到如何执行此查询的示例.
I keep getting Error 102: a valid pointer is needed for RelatedTo operator. My guess is that since I am starting with an empty object it has no starting point. The example with Teacher must start with a populated instance. The only thing that I have that is populated is PFUser. There has to be a way to query for the Item instances and filter it on the "owners" relation that it owns to the current user. I cannot figure it out and I have not found an example of how to do this query.
Parse.com上也有此问题: https://parse.com/questions/how-do-i-query-using-pfrelation-when-i-just-have-pfuser
This question is also on Parse.com: https://parse.com/questions/how-do-i-query-using-pfrelation-when-i-just-have-pfuser
推荐答案
您可以在关系列上使用whereKey:equalTo:并将其传递给PFObject.然后，此查询将返回在其"students"关系中具有此student的所有Teacher对象:
You can use whereKey:equalTo: on a relation column and pass it a PFObject. This query will then return all Teacher objects which have this student in their "students" relation:
PFQuery *query = [PFQuery queryWithClassName:@"Teacher"];
[query whereKey:@"students" equalTo:student];
PFQuery *query = [PFQuery queryWithClassName:@"Teacher"];
[query whereKey:@"students" equalTo:student];
在此示例中，student是具有与"students"中的关系匹配的className的PFObject.如果这是PFUser的关系，并且您正在查找当前用户的"Teacher"，请使用:
In this example, the student is a PFObject with a className that matches the relation in "students". If this is a relation of PFUsers and you're looking for the current user's "Teacher"s, you'd use:
PFQuery *query = [PFQuery queryWithClassName:@"Teacher"];
[query whereKey:@"students" equalTo:[PFUser currentUser]];
PFQuery *query = [PFQuery queryWithClassName:@"Teacher"];
[query whereKey:@"students" equalTo:[PFUser currentUser]];
此答案还发布在Parse的社区论坛上: https://parse.com/questions/how-do-i-query-using-pfrelation-when-i-just-have-pfuser
This answer also posted on Parse's community forums: https://parse.com/questions/how-do-i-query-using-pfrelation-when-i-just-have-pfuser
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