Json handling in ROBOT

The simplest solution would be to write a python keyword that can change the value for you. However, you can solve this with robot keywords by performing the following steps:

1. convert the JSON string to a dictionary
2. modify the dictionary
3. convert the dictionary back to a JSON string

Convert the JSON string to a dictionary

Python has a module (json) for working with JSON data. You can use the evaluate keyword to convert your JSON string to a python dictionary using the loads (load string) method of that module.

Assuming your JSON data is in a robot variable named ${json_string}, you can convert it to a python dictionary like this:

${json}=    evaluate    json.loads('''${json_string}''')    json

With the above, ${json} now holds a reference to a dictionary that contains all of the json data.

Modify the dictionary

The Collections library that comes with robot has a keyword named set to dictionary which can be used to set the value of a dictionary element. In this case, you need to change the value of a dictionary nested inside the vt element of the JSON object. We can reference that nested dictionary using robot’s extended variable syntax.

For example:

set to dictionary    ${json["vt"]}    dp=the new value

With that, ${json} now has the new value. However, it is still a python dictionary rather than JSON data, so there’s one more step.

Convert the dictionary back to JSON

Converting the dictionary back to JSON is the reverse of the first step. Namely, use the dumps (dump string) method of the json module:

${json_string}=    evaluate    json.dumps(${json})    json

With that, ${json_string} will contain a valid JSON string with the modified data.

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Complete example

The following is a complete working example. The JSON string will be printed before and after the substitution of the new value:

*** Settings ***
Library    Collections

*** Test Cases ***
Example
    ${json_string}=    catenate
    ...  {
    ...    "p": "10",
    ...    "v": 100,
    ...    "vt": {
    ...            "dp": "Field to be edited"
    ...          }
    ...  }

    log to console       \nOriginal JSON:\n${json_string}
    ${json}=             evaluate        json.loads('''${json_string}''')    json
    set to dictionary    ${json["vt"]}    dp=the new value
    ${json_string}=      evaluate        json.dumps(${json})                 json
    log to console       \nNew JSON string:\n${json_string}