Expressions and code

Query JSON with JMESPath

Duaer queries JSON with $jmespath(object, "query"). Expressions and the JavaScript Code node can call it. The Python Code node does not have this function.

What $jmespath reads

The first argument is the object to query, usually $json or one item from an earlier node. The second argument is a JMESPath string. The query runs on this execution’s data and does not change the original item.

When a dot path is enough, write $json.body.city. Use JMESPath when you need to filter an array or project fields.

{{ $jmespath($json, "body.city") }}

Where you can call it

A Duaer expression can call $jmespath().
A JavaScript Code node can call it too.
The Python Code node has no $jmespath. Read fields with Python dictionaries and lists.

Questions

How many arguments does Duaer $jmespath take?

Duaer $jmespath(object, "query") takes two arguments. The first is the JSON to query, usually $json. The second is a JMESPath string. The query does not change the original item.

Can a Python Code node call Duaer $jmespath?

No. Duaer $jmespath is available in expressions and in the JavaScript Code node. The Python Code node does not have this function. Read fields with Python dictionaries and lists.

In this section

Define reusable variables in Duaer

Duaer variables store a value for more than one digital organization. Expressions and the Code node read them as $vars.key. Every variable is a string, and a run only reads it.

Write expressions in Duaer

A Duaer expression sits inside {{ }} and reads the current item, earlier nodes, and variables from a node parameter. When you are only reshaping fields, prepare them in an Edit Fields (Set) node first.

Built-in methods and variables in Duaer expressions

Duaer expressions provide variables for reading data and methods you call on a value. The Code node runs plain JavaScript and native Luxon. A method that is a Duaer extension may be missing there, or take different arguments.

Convenience methods in Duaer expressions

Duaer expressions use $json for the current item, $("Node name") for an earlier node, and $now and $if() for time and conditions. These names are available in expression mode on a parameter.

Variables for HTTP node pagination

The Duaer HTTP Request node provides $pageCount, $request, and $response in pagination expressions. Those three names work only in that node. Other nodes cannot read them.

Data transformation methods by type

Duaer expressions call transformation methods on a value, such as {{ $json.name.toTitleCase() }}. The methods are grouped by array, boolean, date, number, object, and string. The Code node does not have these extensions.

Array transformation methods

In a Duaer expression, call an array method on the array, such as {{ $json.ids.unique() }}. average, max, and min throw if any element is not a number.

Boolean transformation methods

In a Duaer expression, a boolean can be tested for empty and converted to a number or a string. true becomes 1 as a number. false becomes 0.

Date transformation methods

In a Duaer expression, $now and $today are Luxon DateTime values. Call toDateTime() on a string or number before format, plus, or setZone.

Number transformation methods

In a Duaer expression, number methods round, test even or odd, and convert to a boolean, a string, or a DateTime. round goes to the nearest number. ceil goes up. floor goes down.

Object transformation methods

In a Duaer expression, object methods test fields, drop fields, merge objects, and encode an object as a query string. keys() and values() return the field names and the values.

String transformation methods

In a Duaer expression, string methods change case, slice text, test emails and URLs, and encode or decode base64 and URLs. Call the method on the string.

Use Luxon for dates in expressions

Dates in a Duaer expression are Luxon DateTime values. $now and $today are DateTime values already. The Code node uses native Luxon. format() and plus(amount, unit) do not carry over unchanged.

Duaer expression examples

These examples run in Duaer expression mode. They read the current item, fill a default, format a date, and move a large reshape into Edit Fields (Set).

Methods and variables reference

These are the names used most often in a Duaer expression. The current item is $json, an earlier node is $("Node name"), variables are $vars, and transformation methods are grouped by data type.