java - Firebase 数据库查询结合 orderByChild 和 startAt 不返回任何内容

Question

我正在尝试使用以下查询来查询 firebase 数据库:

Query test = mDatabase.orderByChild("creation_date").startAt("-L9H3X-qZZt5WiAdsOKE");

我的数据如下所示:

-L9H2ea9Ygt0pD5f17Ze
    creation_date: 
        20180904
    post_id:
        -L9H2ea9Ygt0pD5f17Ze

-L9H3Dmw9gn9lUOV10hK
    creation_date: 
        20180403
    post_id:
        -L9H3Dmw9gn9lUOV10hK

-L9H3OiIzjegJJuuFSfB
    creation_date: 
        20180302
    post_id:
        -L9H3OiIzjegJJuuFSfB

-L9H3X-qZZt5WiAdsOKE
    creation_date: 
        20180404
    post_id:
        -L9H3X-qZZt5WiAdsOKE

-L9JmFch2lnftlMHHiQd
    creation_date: 
        20180405
    post_id:
        -L9JmFch2lnftlMHHiQd

-L9JueI5x9oFRhOX6a3G
    creation_date: 
        20180405
    post_id:
        -L9JueI5x9oFRhOX6a3G

我知道订购后它看起来像这样:

-L9H3OiIzjegJJuuFSfB
    creation_date: 
        20180302
    post_id:
        -L9H3OiIzjegJJuuFSfB

-L9H3Dmw9gn9lUOV10hK
    creation_date: 
        20180403
    post_id:
        -L9H3Dmw9gn9lUOV10hK

-L9H3X-qZZt5WiAdsOKE
    creation_date: 
        20180404
    post_id:
        -L9H3X-qZZt5WiAdsOKE

-L9JmFch2lnftlMHHiQd
    creation_date: 
        20180405
    post_id:
        -L9JmFch2lnftlMHHiQd

-L9JueI5x9oFRhOX6a3G
    creation_date: 
        20180405
    post_id:
        -L9JueI5x9oFRhOX6a3G

-L9H2ea9Ygt0pD5f17Ze
    creation_date: 
        20180904
    post_id:
        -L9H2ea9Ygt0pD5f17Ze

我希望查询返回最后四个元素，但它不返回任何内容。

我还添加了有关 Firebase 安全规则的索引。

谁能帮我找出我做错了什么？

Answer 1

您需要按子项的值进行排序:

Query test = mDatabase.orderByChild("creation_date").startAt(20180904);

这是-L9H3X-qZZt5WiAdsOKE随 secret 钥，它是子creation_date的父节点