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Define unique IDs with externalId

The external ID field, (externalId), is available in API v1 for time series, assets, events, files, and sequences. It lets you define a unique ID for each data object in Cognite Data Fusion (CDF) as an optional extension to the existing id field.

The purpose of external IDs is to:

  • Avoid duplicates when you insert data.
  • Avoid extra lookups when you update data.
  • Maintain relationships between data objects from source systems.
  • Use the time series name field for display instead of lookup.
  • Give you a way of performing key-value lookups with keys you control that works the same across resources.

Make sure to set an externalId on all CDF resources for better performance.

Properties of external IDs​

The external ID is unique per resource type. An asset with externalId=123 will not interfere with a time series with externalId=123.

If you try to create a data object with an existing external ID for a resource type, you'll cause an error.

The field is optional and mutable, so users can choose to add external IDs to data objects that already exist in CDF. If you try to update the external ID to an existing external ID, you'll cause an error.

An empty external ID isn't treated as a unique value.

The external ID limits to 255 characters, and leading and trailing white spaces aren't allowed. The external ID is case-sensitive.

Migrate from earlier API versions​

For time series created in earlier versions of the API, the name field was unique, and the externalId field automatically populated with the value of the name field. The external ID is mutable, and you can override this value.

All other resource types created in earlier API versions will start with an empty externalId field.

Key collisions​

When you populate the external IDs, it's important that you build a structure in each ID that avoids key collisions. For example, some databases use incrementing integers as row keys, and it's probably a good idea to use for instance <database name>/<table name>/<row key> as the external ID instead of just the row key.

ID vs. external ID​

The existing id field, which is a pseudo-random integer between 1 and 2^53-1, remains a valid way of doing a key-value lookup on data objects in CDF. All data objects still have an id, and externalId is an optional extension that lives side-by-side with it.

You can't specify both the id and the externalId in the same object when you do lookups. However, batch lookups in the same request, for example /byids, can mix id and externalId if each object has only one of the fields.

CDF does not support external IDs in GET requests to /resource/:externalId, as it does with the existing id field. You must use the POST resource/byids endpoint instead.

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