JSON Filters
JSON filters are used to manipulate JSON objects, often API responses.
toJson
The toJson filter will convert any object to a JSON string.
The following expression {{ [1, 2, 3] | toJson }} will result in the JSON string '[1, 2, 3]'.
Similarly:
{{ true | toJson }}will result in'true'{{ "foo" | toJson }}will result in'"foo"'
If you were using Kestra in a version prior to v0.18.0, this filter used to be named json. We've renamed it to toJson for more clarity. The renaming has been implemented in a non-breaking way — using json will raise a warning in the UI but it will still work.
jq
The jq filter apply a JQ expression to a variables. The filter always return an array of result and will be formatted as json. You can use the filter first in order to return the first (and potentially the only) result of the jq filter.
{{ [1, 2, 3] | jq('.') }}
{# results in: '[1, 2, 3]' #}
{{ [1, 2, 3] | jq('.[0]') | first }}
{# results in: '1' #}
Another example, if the current context is:
{
"outputs": {
"task1": {
"value": 1,
"text": "awesome1"
},
"task2": {
"value": 2,
"text": "awesome2"
}
}
}
{{ outputs | jq('.task1.value') | first }}
the output will be 1.
Arguments
expression: the jq expression to apply
Manipulating JSON payload
Here is a detailed example having multiple JSON manipulations. In this example, we take a JSON payload as input, and perform multiple manipulations on it to derive different outputs.
id: myflow
namespace: company.myteam
inputs:
- id: payload
type: JSON
defaults: |-
{
"name": "John Doe",
"score": {
"English": 72,
"Maths": 88,
"French": 95,
"Spanish": 85,
"Science": 91
},
"address": {
"city": "Paris",
"country": "France"
},
"graduation_years": [2020, 2021, 2022, 2023]
}
tasks:
- id: print_status
type: io.kestra.plugin.core.log.Log
message:
- "Student name: {{ inputs.payload.name }}" # Extracting a value from a JSON payload
- "Score in languages: {{ inputs.payload.score.English + inputs.payload.score.French + inputs.payload.score.Spanish }}" # Extracting the numbers from JSON payload, and suming them up
- "Total subjects: {{ inputs.payload.score | length }}" # Counting the length of map
- "Total score: {{ inputs.payload.score | values | jq('reduce .[] as $num (0; .+$num)') | first }}" # logic to get all the values in the `score` map and add them to get the total score
- "Complete address: {{ inputs.payload.address.city }}, {{ inputs.payload.address.country | upper }}" # String concatenation, and conversion
- "Total years for graduation: {{ inputs.payload.graduation_years | length }}" # Counting the length of array
- "Started college in: {{ inputs.payload.graduation_years | first }}" # Getting the first value from an array
- "Completed college in: {{ inputs.payload.graduation_years | last }}" # Getting the last value from an array
This flow will log the following statements:
Student name: John Doe
Score in languages: 252
Total subjects: 5
Total score: 431
Complete address: Paris, FRANCE
Total years for graduation: 4
Started college in: 2020
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