Getting a single value from a JSON object using JS

问题:

I have the following JSON and I need to get the plain name value using JSONPath:

{
  "single" : {
    "id" : 1, 
    "name" : "Item name"
  }
}

Expression that I used is $.single.name but I always get an array:

[ "Item name" ]

instead of a string value ("Item name").

回答1:

but I always get an array:

That is meant to happen. As you can read in this documentation, under 'Result' (almost at the bottom):

Please note, that the return value of jsonPath is an array, which is also a valid JSON structure. So you might want to apply jsonPath to the resulting structure again or use one of your favorite array methods as sort with it.

So basically it will always return an array. If you need the data as an other type, e.g. a String in this case, you will have to do the conversion yourself I'm afraid.

回答2:

I was using the Java implementation of JSONPath and got to the very same issue. What worked for me was to add '[0]' to the json path string. So in your case:

$.single.name[0]

回答3:

I know this is an old question , but the following worked for me when writing unit test for a spring boot application. Hope this helps someone in a similar situation.

As Tim Castelijns mentioned , the result is always an array.

Sample Json

{
  "validationErrors": [
    {
      "field": "location",
      "message": "must not be null"
    },
    {
      "field": "address",
      "message": "must not be blank"
    },
    {
      "field": "id",
      "message": "must be null"
    },
    {
      "field": "name",
      "message": "must not be blank"
    }
  ]
}

and the unit test part

//verify if the id is validated for null
andExpect((ResultMatcher) jsonPath("$.validationErrors[?(@.field=='id')].message").isArray()).
andExpect((ResultMatcher) jsonPath("$.validationErrors[?(@.field=='id')].message",hasItem("must be null"))).

回答4:

I think, it depends of language implementation.

For example in nodejs there is a npm module : https://www.npmjs.com/package/jsonpath

Which have a method called value, which does exactly what we need

jp.value(obj, pathExpression[, newValue])

Returns the value of the first element matching pathExpression. If newValue is provided, sets the value of the first matching element and returns the new value.

I tried it and worked!