JSON: advanced features - filtering a list & returning a value

Overview

You have an item that is returned in a JSON list but rather than being in a specific location in the list i.e. foo.[2].bar - it could be in any location in the list. Using a filter to identify the item, and then extracting that as a variable is how we handle this scenario.

Summary

The Assertion checks syntax uses a cut-down version of the Jinja templating library to parse the data, which allows for some filters (marked by |) and tests as well as the direct dot-notation syntax.

For example, consider the following JSON:

{
  "headers": [
    {
      "key": "Content-Type",
      "value: "application/json"
    },
    {
      "key": "Interaction-Id",
      "value: "123456789123456789"
    },
    {
      "key": "X-APImetrics-Id",
      "value": "asdfasdfasdfasdf"
    }
  ]
}

In this JSON, the headers are in a list. If that list is always in the same order, you can use the regular notation to find the value associated with the key Interaction-Id:

headers[1].value

However, if this list is not in a guaranteed order, you need to use filters and tests to get the value you require.

In the above example, to get the Interaction-Id, you'd use the following assertion:

headers|selectattr("key", "eq", "Interaction-Id")|map(attribute="value")|first

To explain:

the selectattr filters the list of header objects where the object has an attribute key, that is equal to Interaction-Id - this will reduce the headers list to the a list containing the one matching item
the map with attribute extracts the value for the filtered list - this will leave a list with one item that is the value we want
the first returns the first item in the list

For the full list of filters and tests, see the JSON filters and tests reference.

Use Case

In this example, we have a sample returned JSON list where we want to find the Interaction ID and extract that as a variable for use in another call.

Sample returned JSON with a headers array containing the Interaction-Id key to be filtered and extracted

The first step is to set up an assertion check to create a filter and check that the item exists.

We do this in the 'assertions' section of the API edit pane.

json.headers|selectattr("key", "eq", "Interaction-Id")|map(attribute="value")|first

We set the ASSERTION to test it exists using the filter string in the test, thus:

We then add the command to EXTRACT the value: First we set the search criteria to find the value Interaction id.

json.headers|selectattr("key", "eq", "Interaction-Id")|map(attribute="value")|first

And then set the EXTRACT conditions to set the variable you use.

Your assertions section of the edit pane should look something like this:

Assertions Response Body section showing both the Assert exists check and the Extract to INTERACTION_ID rows

When the monitor is run, the variable INTERACTION_ID is set to the value of the Interaction id in the returned JSON.

This can be used in another call in a workflow using %%INTERACTION_ID%% or INTERATION_ID

Overview​

Summary​

Use Case​

Overview

Summary

Use Case