JMESpath 表达式按属性过滤对象并返回设置了此属性的对象名称列表 [英] JMESpath expression to filter object by property and return list of object names having this property set

问题描述

是否可以编写 JMESPath 表达式来返回设置了特定子属性值的对象名称列表?在下面的示例中，我想获取 fileexists.stat.exists 设置为 true 的所有主机名的列表.

我的目标是使用 Ansible 主机变量结构来获取存在特定文件的所有主机的列表.

<代码>{主机变量":{oclab1n01.example.org":{文件已存在": {改变":假，失败":错误，统计":{存在":假}}},oclab1n02.example.org":{文件已存在": {改变":假，失败":错误，统计":{存在":真实}}},oclab1n03.example.org":{文件已存在": {改变":假，失败":错误，统计":{存在":真实}}}} }

在这个例子中，我想得到以下输出

["oclab1n02.example.org", "oclab1n03.example.org"]

解决方案

Short answer (TL;DR)

是的，这是可能的，但它非常麻烦，因为至少在使用 JMESpath 方面，源数据集对于这种通用查询标准化很差.>

上下文

• jmespath 查询语言
• 查询深度嵌套对象的对象属性

问题

• 如何使用过滤器表达式构建 jmespath 查询
• 目标是过滤具有任意嵌套对象属性的对象

解决方案

• 这个可以用jmespath来完成，但是操作起来会繁琐
• 一个有问题的问题:对于这种 jmespath 查询，源数据集标准化不佳
• 为了构建 jmespath 查询，我们必须假设所有主对象键在创建查询之前都是已知的
• 在这个特定的例子中，我们必须在构建 jmespath 查询之前知道只有三个主机名 ...如果我们想要灵活地指定，这不是一个有利的情况任意数量的主机名

示例

以下(太大了)jmespath 查询...

<预><代码> [{主机名":`oclab1n01.example.org`,fileexists_stat_exists":@.hostvars.oclab1n01.example.org".fileexists.stat.exists},{主机名":`oclab1n02.example.org`,fileexists_stat_exists":@.hostvars.oclab1n02.example.org".fileexists.stat.exists},{主机名":`oclab1n03.example.org`,fileexists_stat_exists":@.hostvars.oclab1n02.example.org".fileexists.stat.exists}]|[?@.fileexists_stat_exists == `true`]|[*].hostname

返回以下想要的结果

<预><代码> [oclab1n02.example.org"，oclab1n03.example.org"]

陷阱

• 此用例的一个主要缺陷是源数据集标准化不佳用于此类查询
• 更扁平的数据结构将更容易查询
• 因此，如果可能，更好的方法是在对源数据集运行 jmespath 查询之前将其展平

具有不同原始数据集的替代示例

如果将原始数据组织为对象列表，而不是对象内的一组嵌套对象，则无需事先知道即可更轻松地搜索、排序和过滤列表涉及多少主机名条目.

{hostvars":[{主机名":oclab1n01.example.org",文件存在":真,文件已更改":false,文件失败":假,filestat_exists":假，we_can_even_still_deeply_nest":{但是":{im_only_doing":它在这里"，to":证明一个点"}}},{主机名":oclab1n02.example.org",文件存在":真,文件已更改":false,文件失败":假,filestat_exists":真},{主机名":oclab1n03.example.org",文件存在":真,文件已更改":false,文件失败":假,filestat_exists":真}]}

现在可以轻松查询上述重新归一化数据集

hostvars|[?@.filestat_exists == `true`]|[*].hostname

Is it possible to write JMESPath expression to return a list of object names where a specific subproperty value is set? In the example below I'd like to get a list of all hostsnames where fileexists.stat.exists is set to true.

My goal is to use Ansible hostvars structure to get a list of all hosts where a specific file is present.

{
"hostvars": {
    "oclab1n01.example.org": {
        "fileexists": {
            "changed": false, 
            "failed": false, 
            "stat": {
                "exists": false
            }
        }
    }, 
    "oclab1n02.example.org": {
        "fileexists": {
            "changed": false, 
            "failed": false, 
            "stat": {
                "exists": true
            }
        }
    }, 
    "oclab1n03.example.org": {
        "fileexists": {
            "changed": false, 
            "failed": false, 
            "stat": {
                "exists": true
            }
        }
    }
} }

In this example I'd like to get the following output

["oclab1n02.example.org", "oclab1n03.example.org"]

解决方案

Short answer (TL;DR)

Yes, this is possible, but it is extremely cumbersome, because, at least in terms of working with JMESpath, the source dataset is poorly normalized for this kind of general-purpose query.

Context

• jmespath query language
• querying object properties for deeply nested objects

Problem

• How to construct a jmespath query with filter expressions
• The goal is to filter on objects with arbitrarily nested object properties

Solution

• This can be done with jmespath, but the operation will be cumbersome
• One problematic issue: the source dataset is poorly normalized for this kind of jmespath query
• In order to construct the jmespath query, we have to assume all the primary object keys are known in advance of creating the query
• In this specific example, we have to know that there are three and only three hostnames in advance of constructing the jmespath query ... this is not a favorable circumstance if we want the flexibility to specify any arbitrary number of hostnames

Example

The following (way-too-huge) jmespath query ...

  [
    {
      "hostname": `oclab1n01.example.org`
      ,"fileexists_stat_exists":  @.hostvars."oclab1n01.example.org".fileexists.stat.exists
    }
    ,{
      "hostname": `oclab1n02.example.org`
      ,"fileexists_stat_exists":  @.hostvars."oclab1n02.example.org".fileexists.stat.exists
    }
    ,{
      "hostname": `oclab1n03.example.org`
      ,"fileexists_stat_exists":  @.hostvars."oclab1n02.example.org".fileexists.stat.exists
    }
  ]|[? @.fileexists_stat_exists == `true`]|[*].hostname

returns the following desired result

  [
    "oclab1n02.example.org",
    "oclab1n03.example.org"
  ]

Pitfalls

• One major pitfall with this use-case is the source dataset is poorly normalized for this kind of query
• A more flattened data structure would be easier to query
• Consequently, if possible, a better approach would be to flatten the source dataset before running jmespath queries against it

Alternate example with a different original dataset

If the original data were organized as a list of objects, instead of a set of nested objects within objects, it would be easier to search, sort and filter the list without having to know in advance how many hostname entries are involved.

{"hostvars": [
    {"hostname":"oclab1n01.example.org"
      ,"fileexists":        true
      ,"filechanged":       false
      ,"filefailed":        false
      ,"filestat_exists":   false
      ,"we_can_even_still_deeply_nest":{"however":
           {"im_only_doing":"it here","to":"prove a point"}
         }
     }
    ,{"hostname":"oclab1n02.example.org"
      ,"fileexists":        true
      ,"filechanged":       false
      ,"filefailed":        false
      ,"filestat_exists":   true
     }
    ,{"hostname":"oclab1n03.example.org"
      ,"fileexists":        true
      ,"filechanged":       false
      ,"filefailed":        false
      ,"filestat_exists":   true
     }
  ]
}

The above re-normalized dataset can now be easily queried

hostvars|[? @.filestat_exists == `true`]|[*].hostname

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