问题描述
我有下图中的结构，我想从id_Usuario"查询的节点aaa1234"中获取全部数据.我该怎么做这个查询?
I have the structure in the image below and I want to get the whole data from the node "aaa1234" querying by "id_Usuario". How can I do that query?
我试过了:
DatabaseReference root = database.getReference().child("Eventos").child("participantes");
Query query = root.orderByChild("id_Usuario").equalTo(2);
为了更清楚一点，aaa1234"是自定义键，所以在下一个节点会有所不同.
Just to be more clear, the "aaa1234" is a custom key, so it will be different in the next node.
推荐答案
我看到了两个错误.
第一个是错字，我已经在评论中标明了.您将用户 ID 存储为数字，因此不应该在 equalTo 中的值周围加上引号.所以:.equalTo(2)
The first one is a typo, which I already marked in my comment. You're storing the user ID as a number, so shouldn't have quotes around the value in equalTo. So: .equalTo(2)
第二个错误是你尝试查询的方式:
The second mistake is in the way you try to query:
DatabaseReference root = database.getReference().child("Eventos").child("participantes");
这将创建对不存在的子 Eventos/participantes 的引用.你想要做的是查询 Eventos，然后查询属性 participantes/id_Usuario.所以
This will create a reference to the non-existing child Eventos/participantes. What you want to do instead is query Eventos, but then against property participantes/id_Usuario. So
DatabaseReference root = database.getReference().child("Eventos");
Query query = root.orderByChild("participantes/id_Usuario").equalTo(2);
这篇关于从 Firebase 实时数据库 Android 查询嵌套数据的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！