A query to get a JSON element on an object with JMESPATH

Question

When I have a simple JSON like:

{
    "name": "Tom",
    "age": 20
}

Is there any JMESPath query to get age only when name is Tom?

The query should get 20 with the upper JSON.

But, if the name is not Tom like:

{
    "name": "Bob",
    "age": 31
}

The query should return null.

Answer 1

In order to filter, you will need an array.
And you can get an array from any object with the function to_array.

Then, because you have an unique object, you can stop the projection created by the filter, and, take the first element of the array, using | [0], as explained in the pipe expressions section of the tutorial.

So with the query:

to_array(@)[?name == `Tom`].age | [0]

• This will give 20 for the JSON

  {
    "name": "Tom",
    "age": 20
  }
  

• This will give null for the JSON

  {
    "name": "Bob",
    "age": 31
  }