如何用jq递归转换json树？答案

【问题标题】：How to transform json tree recursively with jq?如何用jq递归转换json树？
【发布时间】：2020-11-11 13:44:31
【问题描述】：

我有以下需要用 jq 转换的 JSON。主要任务是在树中只保留指定的属性。树中的层数可能不同。

    {
    "metaModel": [ {
        "clazz": "AttributeClass1",
        "code": "code1",
        "default": "value1",
        "children": [ {
            "clazz": "AttributeClass2",
            "code": "code21",
            "default": "value21"
        },
        {
            "clazz": "AttributeClass1",
            "code": "code22",
            "default": "value22",
            "children": [ {
                "clazz": "AttributeClass1",
                "code": "code31",
                "default": "value31",
                "children": []
            }
            ]
        }
        ]
    },
    {
        "clazz": "AttributeClass2",
        "code": "code2",
        "default": "value2"
    }
    ]
}

是否有可能得到如下输出（只留下 clazz、code、children）？

    {
        "clazz": "AttributeClass1",
        "code": "code1",
        "children": [ {
            "clazz": "AttributeClass2",
            "code": "code21"
        },
        {
            "clazz": "AttributeClass1",
            "code": "code22",
            "children": [ {
                "clazz": "AttributeClass1",
                "code": "code31",
                "children": []
            }
            ]
        }
        ]
    },
    {
        "clazz": "AttributeClass2",
        "code": "code2"
    }

'metaModel' 也可能留在输出中。

【问题讨论】：

标签： json recursion tree jq

【解决方案1】：

使用walk/1：

.metaModel
| walk( if type == "object" and has("clazz")
        then {clazz, code} + (if .children then { children } else null end )
        else .
        end )

【讨论】：

【解决方案2】：

下面的递归函数似乎满足要求，或者至少过滤器.metaModel | transform按照样本输出对样本输入进行变换：

def transform:
  if type == "object" and has("clazz")
  then  {clazz, code} + (if has("children") then {children: (.children|transform)} else null end)
  elif type == "array" then map(transform)
  else .
  end;

脚注

如果你不喜欢表达式的冗余

{children: (.children|transform)}

你可以写：

{children} | map_values(transform)

【讨论】：

【解决方案3】：

这是一种使用tostream、setpath和reduce的方法：

reduce (tostream|select(.[0][-1]|.=="clazz" or .=="code" or .=="children")) as [$p,$v] (
  {}; setpath($p;$v)
)

Try it online!

tostream 将您的输入转换为“流”[path,value] 形式：

[["metaModel",0,"children",0,"clazz"],"AttributeClass2"]
[["metaModel",0,"children",0,"code"],"code21"]
[["metaModel",0,"children",0,"default"],"value21"]
[["metaModel",0,"children",0,"default"]]
[["metaModel",0,"children",1,"children",0,"children"],[]]
[["metaModel",0,"children",1,"children",0,"clazz"],"AttributeClass1"]
[["metaModel",0,"children",1,"children",0,"code"],"code31"]
[["metaModel",0,"children",1,"children",0,"default"],"value31"]
[["metaModel",0,"children",1,"children",0,"default"]]
[["metaModel",0,"children",1,"children",0]]
[["metaModel",0,"children",1,"clazz"],"AttributeClass1"]
[["metaModel",0,"children",1,"code"],"code22"]
[["metaModel",0,"children",1,"default"],"value22"]
[["metaModel",0,"children",1,"default"]]
[["metaModel",0,"children",1]]
[["metaModel",0,"clazz"],"AttributeClass1"]
[["metaModel",0,"code"],"code1"]
[["metaModel",0,"default"],"value1"]
[["metaModel",0,"default"]]
[["metaModel",1,"clazz"],"AttributeClass2"]
[["metaModel",1,"code"],"code2"]
[["metaModel",1,"default"],"value2"]
[["metaModel",1,"default"]]
[["metaModel",1]]
[["metaModel"]]

select 过滤掉所有不以“clazz”、“code”或“children”结尾的路径：

[["metaModel",0,"children",0,"clazz"],"AttributeClass2"]
[["metaModel",0,"children",0,"code"],"code21"]
[["metaModel",0,"children",1,"children",0,"children"],[]]
[["metaModel",0,"children",1,"children",0,"clazz"],"AttributeClass1"]
[["metaModel",0,"children",1,"children",0,"code"],"code31"]
[["metaModel",0,"children",1,"clazz"],"AttributeClass1"]
[["metaModel",0,"children",1,"code"],"code22"]
[["metaModel",0,"clazz"],"AttributeClass1"]
[["metaModel",0,"code"],"code1"]
[["metaModel",1,"clazz"],"AttributeClass2"]
[["metaModel",1,"code"],"code2"]

reduce 和 setpath 重构最终结果：

{
  "metaModel": [
    {
      "children": [
        {
          "clazz": "AttributeClass2",
          "code": "code21"
        },
        {
          "children": [
            {
              "children": [],
              "clazz": "AttributeClass1",
              "code": "code31"
            }
          ],
          "clazz": "AttributeClass1",
          "code": "code22"
        }
      ],
      "clazz": "AttributeClass1",
      "code": "code1"
    },
    {
      "clazz": "AttributeClass2",
      "code": "code2"
    }
  ]
}

【讨论】：