---
title: "Contact identifiers"
slug: "contact-identifiers"
abstract: "Introduction to adding a custom contact identifier when mapping data from MongoDB to xConnect in xDB Data Migration Tool."
---
# Contact identifiers

In the section [Entity facets](https://doc.sitecore.com/xp/en/developers/dmt/50/xdb-data-migration-tool/entity-facets.html "Entity facets"), the membership id for a customer loyalty program was set as a property on a contact facet. If you do not need to search for a contact using the membership id, a contact facet is a good place to store the value.

However, if you expect to search for a contact using the membership id, you will want to add the value as an identifier on the contact. This section explains how to configure xDB Data Migration Tool to create a custom contact identifier using the membership id.

> [!note]
> This section assumes that you have completed the steps in the section [Entity facets](https://doc.sitecore.com/xp/en/developers/dmt/50/xdb-data-migration-tool/entity-facets.html "Entity facets").

- [Determine the data for the contact identifier](https://doc.sitecore.com/xp/en/developers/dmt/50/xdb-data-migration-tool/determine-the-data-for-the-contact-identifier.html "Determine the data for the contact identifier")
- [Map data from MongoDB to contact identifier](https://doc.sitecore.com/xp/en/developers/dmt/50/xdb-data-migration-tool/map-data-from-mongodb-to-contact-identifier.html "Map data from MongoDB to contact identifier")
    - [Specify value for xConnect contact identifier source](https://doc.sitecore.com/xp/en/developers/dmt/50/xdb-data-migration-tool/contact-identifiers.html#UUID-f84bb791-534a-e343-e68a-20b0fd20edbe_N1530023760047)
    - [Add mapping for xConnect contact identifier constructor](https://doc.sitecore.com/xp/en/developers/dmt/50/xdb-data-migration-tool/contact-identifiers.html#UUID-f84bb791-534a-e343-e68a-20b0fd20edbe_N1530023782259)
    - [Add value accessor for custom identifier](https://doc.sitecore.com/xp/en/developers/dmt/50/xdb-data-migration-tool/contact-identifiers.html#UUID-f84bb791-534a-e343-e68a-20b0fd20edbe_N1530023797149)
    - [Add mapping for xConnect contact identifier to entity model for contact](https://doc.sitecore.com/xp/en/developers/dmt/50/xdb-data-migration-tool/contact-identifiers.html#UUID-f84bb791-534a-e343-e68a-20b0fd20edbe_N1530023818429)
- [Run pipeline batch](https://doc.sitecore.com/xp/en/developers/dmt/50/xdb-data-migration-tool/run-pipeline-batch-487744.html "Run pipeline batch")
    - [xConnect collection database](https://doc.sitecore.com/xp/en/developers/dmt/50/xdb-data-migration-tool/contact-identifiers.html#UUID-f84bb791-534a-e343-e68a-20b0fd20edbe_N1530023834969)
    - [xConnect client](https://doc.sitecore.com/xp/en/developers/dmt/50/xdb-data-migration-tool/contact-identifiers.html#UUID-f84bb791-534a-e343-e68a-20b0fd20edbe_N1530023854376)