如何指定JSON解析的数据类型？

Question

我有一个 JSON 响应，它是一个哈希数组：

[{"project" => {"id" => 1, "name" => "Internal"},
 {"project" => {"id" => 2, "name" => "External"}}]

我的代码如下所示：

client = HTTP::Client.new(url, ssl: true)
response = client.get("/projects", ssl: true)
projects = JSON.parse(response.body) as Array

我试过 as Array(Hash) 但这给了我 can't use Hash(K, V) as generic type argument yet, use a more specific type.

如何指定类型？

Answer 1

您必须在访问元素时强制转换这些元素：

projects = JSON.parse(json).as(Array)
project = projects.first.as(Hash)["project"].as(Hash)
id = project["id"].as(Int64)

http://carc.in/#/r/f3f

但是对于像这样结构良好的数据，你最好使用 JSON.mapping:

class ProjectContainer
  JSON.mapping({
    project: Project
  })
end

class Project
  JSON.mapping({
    id: Int64,
    name: String
  })
end

projects = Array(ProjectContainer).from_json(json)
project = projects.first.project
pp id = project.id

http://carc.in/#/r/f3g

您可以在 https://github.com/manastech/crystal/issues/982#issuecomment-121156428

看到关于这个问题的更详细的解释

Answer 2

您每一步都在继续施法：

projects = JSON.parse(response.body) as Array
projects.each do |project|
  project = project as Hash
  project = project["project"] as Hash
  id = project["id"] as Int
  name = project["name"] as String
end

但是如果您的 API 响应具有众所周知的结构，我强烈建议您使用 JSON.mapping：https://crystal-lang.org/api/0.22.0/JSON.html#mapping-macro

如何指定JSON解析的数据类型？

How to specify the data types for JSON parsing?

crystal-lang