JSONPath is a query language for JSON, similar to XPath for XML.
The result of a simple query (also called definite JSONPath) is a single value. The result of a collection query (also called indefinite JSONPath) is a list of multiple values. Results of JSONPath queries are converted to the selected KNIME type. If the result is a list and the selected KNIME type is not compatible, the execution will fail. If the result cannot be converted to the selected KNIME type, a missing value will be returned.
JSONPath queries can be automatically generated via the node configuration dialog. To create a simple query, select a single value from the JSON-Cell Preview window and click "Add single query". To create a collection query, select a value that is part of a list of values from the JSON-Cell Preview window and click "Add collection query". Alternatively, you can write your own JSONPath query by clicking the "Add JSONPath" button.
Example input:{"book": [
{"year": 1999,
"title": "Timeline",
"author": "Michael Crichton"},
{"year": 2000,
"title": "Plain Truth",
"author": "Jodi Picoult"}
]}
Example JSONPath queries and evaluation results:
$.book[0]
{"year": 1999, "title": "Timeline", "author": "Michael Crichton"} ( JSON or String single value)
$.book[*].year
[1999,2000] ( JSON , Int or Real list)
$.book[2].year
? (no such part)
$.book[?(@.year==1999)].title
Timeline ( String ) or "Timeline" ( JSON )
The default path ( $..* ) will select all possible subparts (excluding the whole JSON value).
When you request the paths instead of values for the $.book[0].* JSONPath, you will get the paths -in bracket notation- as a list of Strings:
- $['book'][0]['year']
- $['book'][0]['title']
- $['book'][0]['author']
The filters ?(expr) can be used to select contents with specific properties, for example $..book[?(@.publisher)] selects the books that specify their publisher ( @ refers to the actual element).
The JSON Path node uses the Jayway JSONPath implementation.