ConstantTransformer

Define and add constant values to documents.

importerJavadoc: ConstantTransformer

Notes

To add multiple constant values under the same constant name, repeat the constant entry with a different value.

onSet property determines how constant values are applied to fields that may already exist in a document. It can be configured globally (at the root of the handler) or individually for each constant

Storing values in an existing field

If a document already has a target field with the same name, new values are appended to the existing list by default. Use onSet to manage this default behavior.

Parser Handler Compatibility

This functionality can be applied as either a pre-parse or post-parse handler.

Examples

The following example adds a constant to incoming documents to identify they were web and mobile documents plus a constant number

YAML

handler:
  class: ConstantTransformer
  constants:
    - name: source
      values:
        - web
        - mobile
    - name: limit
      values:
        - "3"

JSON

{
  "handler": {
    "class": "ConstantTransformer",
    "constants": [
      {
        "name": "source",
        "values": [
          "web",
          "mobile"
        ]
      },
      {
        "name": "limit",
        "values": [
          "3"
        ]
      }
    ]
  }
}

XML

<handler>
  <class>ConstantTransformer</class>
  <constants>
    <constant>
      <name>source</name>
      <values>
        <value>web</value>
        <value>mobile</value>
      </values>
    </constant>
    <constant>
      <name>limit</name>
      <values>
        <value>3</value>
      </values>
    </constant>
  </constants>
</handler>

Usage

Full configuration skeleton, with every option and its default

YAML

class: ConstantTransformer
constants:
  - name: string
    onSet: APPEND
    values: []
label: string
onSet: APPEND

JSON

{
  "class": "ConstantTransformer",
  "constants": [
    {
      "name": "string",
      "onSet": "APPEND",
      "values": []
    }
  ],
  "label": "string",
  "onSet": "APPEND"
}

XML

<handler>
  <class>ConstantTransformer</class>
  <constants>
    <constant>
      <name>string</name>
      <onSet>APPEND</onSet>
      <values>
        <value/>
      </values>
    </constant>
  </constants>
  <label>string</label>
  <onSet>APPEND</onSet>
</handler>

Properties

Property	Type	Required	Default
constants	Constant[]	No	-
label	string	No	-
onSet	enum	No	-

Property Details

constants

Manage the constants list

label

An optional, user-supplied label for this step in the importer pipeline. It has no effect on processing — it exists purely to help identify this step, for example in large configurations or in the visual configurator.

onSet

What to do if a target field of the same name already exist.

Allowed Values

• APPEND
• PREPEND
• REPLACE
• OPTIONAL