ios - FIR 数据库查询 : how to do an inner join

Question

我正在尝试对 FIRDatabaseQuery 对象执行内部联接。

下面是数据库结构。我有一些链接到帖子评论的帖子。我正在尝试获取特定用户添加评论的所有帖子:

 {
   "posts" : {
    "-KIycKhZU55dmKnHbbxv" : {
      "author" : "John Doe",
      "body" : "This is a post test",
      "title" : "test",
      "uid" : "SHaH36BLwgPvwgi9cDmRnsnONFB2"
    },
    "-KIyg_ks1O5QL4_4dfq_" : {
      "author" : "Jane Doe",
      "body" : "This is a post test",
      "title" : "test2",
      "uid" : "x5leSBGArnd10JilD9YDyNBNfZ03"
    },...
   }
  "post-comments" : {
    "-KIycKhZU55dmKnHbbxv" : {
      "-KIycMyL0Vy1BHVdI4zc" : {
        "author" : "toto",
        "text" : "test",
        "uid" : "SHaH36BLwgPvwgi9cDmRnsnONFB2"
      },
      "-KIyg_ks1O5QL4_4dfq_" : {
        "author" : "toto",
        "text" : "test",
        "uid" : "SHaH36BLwgPvwgi9cDmRnsnONFB2"
      }
    },...
 }

在 SQL 中，这将被翻译成类似于以下的内部连接查询:

Select * from post inner join post-comments on post-id where post-comments.uid = "user id"

有人知道如何在 firebase 中获得类似于内部连接的东西吗？

非常感谢，亚辛

Answer 1

你可能要考虑

"posts" : {
    "-KIycKhZU55dmKnHbbxv" : {
      "author" : "John Doe",
      "body" : "This is a post test",
      "title" : "test",
      "uid" : "SHaH36BLwgPvwgi9cDmRnsnONFB2"
      "commented_by"
           "SHaH36BLwgPvwgi9cDmRnsnONFB2": true

然后你可以简单地查询

posts.child("commented_by/uid").queryEqualToValue(true)

或者，更改后置评论以更好地匹配您要执行的查询:

"post-comments" : {
  "-KIycMyL0Vy1BHVdI4zc" : {
     "author" : "toto",
     "post_data":
          post_id: "-KIycKhZU55dmKnHbbxv",
          post_title: "test"
     "text" : "test",
     "uid" : "SHaH36BLwgPvwgi9cDmRnsnONFB2"
},

这使得查询变得轻而易举，因为可以查询 post-comments 节点的 uid，该 uid 返回他们评论过的帖子的所有 post_id。它不会返回帖子本身，但是，您可能只是在寻找标题以便填充列表。一旦用户点击它，您就可以检索实际数据。