extract

Use the extract policy to extract and transform data from fields in the API context.

Gateway support

Table 1. Gateways that support this policy and the corresponding policy versions
Gateway	Policy version
DataPower® API Gateway	2.0.0

This topic describes how to configure the policy in your OpenAPI source; for details on how to configure the policy in the assembly user interface, see Extract.

About

The extract policy specifies the data source that contains the content to transform, the fields that contain the content, and expressions that define how to transform the content. You use a subset of JSONata notation to specify the fields to extract and transform. For more information, see Constructing JSONata expressions to extract and transform data.

The input to the extract policy must be parsed data. One way to produce parsed data is to add a parse policy before the extract policy in your assembly.

The extract policy has the following format:

- extract:
    version: 2.0.0
    title: title
    root: data source
    extracts:
      - capture: path expression that identifies the field
        transform: expression that defines how to transform the content
                   .
                   .
                   .
    description: description

Apply this policy by adding an assembly extension with an execute field to your OpenAPI definition file.

Properties

Table 2. extract policy properties
Property label	Required	Description	Data type
version	Yes	The policy version number. You must specify a version for the policy that is compatible with the gateway that you are using. When the API is published, if the version is incompatible with the gateway, a validation error is thrown that specifies the available versions.	string
title	Yes	The title of the policy. The default value is `extract`.	string
description	No	A description of the policy.	string
root	Yes	The data source that contains the content to transform. The default value is `message.body`.	string
capture	Yes	The path expression that identifies the field. The default setting is `$`, which indicates the entire input.	string
transform	Yes	The expression that defines how to transform the content.	string

Example

Transform the contents of the account field to include only the last 4 characters.

- extract:
    version: 2.0.0
    title: extract
    root: message.body
    extracts:
      - capture: $.members.policy.**.account
        transform: $substring($,-4)
    description: Include only the last 4 characters of the account field.