从 Firebase 实时数据库 Android 查询嵌套数据

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);

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