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Advanced Field Mapping with JMESPath
Advanced Field Mapping with JMESPath
Abe Chen avatar
Written by Abe Chen
Updated over a week ago


Merge Field Mapping allows you or your users to map data from your users' platforms to new fields on your Merge Common Models. This way you can access custom fields from third-party platforms that Merge does not normalize.

Advanced Field Mapping is a feature enhancement that allows you to write JMESPath queries to access specific values from a list of objects.

How to access Advanced Mapping

  1. In your Merge Dashboard, go to a Linked Account

  2. Click into the Field Mapping Tab to create a new Field Mapping

  3. When you are selecting from the remote fields dropdown, you will see the "Advanced Mapping" option appear for any fields of type "List"

  1. Expanding Advanced Mapping will allow you to view the full remote field

  2. From here you may use the query input field to write JMESPath queries in order to select specific fields in this List

  3. If you want to select fields in the List using it's index, you can simply click the value that you care about and we will auto generate the query!

JMESPath Basics

You can specify queries using JMESPath.

Index Expressions allow you to select a specific element in a list. It should look similar to array access in common programming languages. Indexing is 0 based.

Functions can also be combined with filter expressions. In the example below, the JMESPath expressions finds all elements in myarray that contains the string foo.

Common Query Examples

In the following example, we want to get personal email

[{ "emailUri": "[email protected]", 
"nameCode": { "codeValue": "Personal E-mail", "shortName": "Personal E-mail" }, "notificationIndicator": false }]

You can generate the query using ChatGPT! Try asking
"Get the email URI only if shortName is Personal E-mail using jmespath and share only the snippet and the outputted value"

  • To get the emailUri by index: "[0].emailUri"

  • To get the emailUri only if shortName is Personal E-mail: [?nameCode.shortName == 'Personal E-mail'].emailUri | [0]

Quotes Matter

Make sure to only double-quote variable names, and single-quote or back-tick-quote anything that is a string literal. This requirement is inconsistent with normal python comparisons. The behavior is strict and unintuitive to people unfamiliar with jmespath. Learn more here.

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