Expression Transformation and Judgment (Filters)

In workflow expressions, the function to perform "transformation" and "judgment" on values ​​is provided as filters.

In general programming terms, it's similar to a function that takes input (value) and returns output (transformed value).

How to Read Filters (Pipe Notation)

The | (pipe) is used to apply filters from left to right.

{{ 'ABC' | to_lower | trim }}

This example means "convert 'ABC' to lowercase and remove leading and trailing whitespace."

Using filters, you can simply write a wide range of data transformations, such as string processing, date and time manipulation, path processing, and hashing.

Basic Filters

Filter Name	Description	Example
size	Returns the number of elements	{{ [1,2,3] | size}} → 3
type	Returns the type name	{{ 123 | type}} → Int32

---

String Manipulation

Filter Name	Description	Example
to_lower/to_upper/trim	Formats strings	{{ 'ABC' | to_lower}} → abc
contains/starts_with/ends_with	Match detection	{{ 'abc' | contains 'b'}} → true
split/join	Split and join	{{ 'a|b|c' | split '|'}} → [a,b,c]
regex_match/regex_replace	Regular expression operation	{{ 'abc' | regex_replace 'a' 'z'}} → zbc
to_base64/from_base64	Base64 conversion	{{ 'abc' | to_base64}} → YWJj
url_encode/url_decode	URL Conversion	{{ 'a b' | url_encode}} → a%20b
sha256/md5	Hashing	{{ 'abc' | sha256}}

---

JSON/YAML

Filter Name	Description	Example
to_json/from_json	JSON Conversion	{{ obj | to_json}}/{{ '{"a":1}' | from_json}}
to_yaml/from_yaml	YAML Conversion	{{ obj | to_yaml}}/{{ 'a: 1' | from_yaml}}

ignoreNulls option allows ignoring null values
Example: {{ obj | to_json { ignoreNulls: true } }}

---

Date and Time Manipulation

Filter Name	Description	Example
now/utcnow	Get Current Date and Time	{{ now }}
add_days/add_hours	Adding Days	{{ '2024-01-01' | add_days 1}} → 2024-01-02
format_date	Date Formatting	{{ '2024-01-01' | format_date 'yyyy/MM/dd'}} → 2024/01/01

---

Collection Operations

Filter Name	Description	Example
sort/reverse	Sort	{{ [3,1,2] | sort}} → [1,2,3]
unique/flatten	Duplicate Removal/Flattening	{{ [[1,2],[3]] | flatten}} → [1,2,3]

---

Path Manipulation

Filter Name	Description	Example
path_filename/path_basename	Filename Manipulation	{{ '/a/b/file.txt' | path_filename}} → file.txt
path_join/path_normalize	Path Manipulation	{{ ['a','b','c.txt'] | path_join}} → a/b/c.txt
path_change_extension	Change extension	{{ '/tmp/data.txt' | path_change_extension '.json'}} → /tmp/data.json

---

Utilities

Filter Name	Description	Example
uuid	Generate UUID	{{ uuid }} → 550e8400-e29b-41d4-a716-446655440000
random	Generate random number	{{ random 1 10 }} → 7
default/coalesce	Default value processing	{{ null | default 'x'}} → x
is_null/is_empty	Judgment Filter	{{ '' | is_empty}} → true

---

Parameterized Filter Notation

{{ obj | to_json { ignoreNulls: true } }}

---

Example of Use

# Decode JSON string and extract items
{{ '{"a":1,"b":2}' | from_json | size }} → 2

# Change file extension from file path
{{ '/tmp/data.txt' | path_change_extension '.json' }} → '/tmp/data.json'

# Format the current date and time
{{ now | format_date 'yyyy-MM-dd HH:mm' }}