Change Data Capture Developer Guide

Change Data Capture
Keep Your External Data Current with Change Data Capture
Change Event Message Structure
Merged Change Events
Other Types of Change Events: Gap and Overflow Events
Subscribe to Change Events
Monitor Change Event Publishing and Delivery Usage
Security Considerations
Change Event Considerations
Standard Object Notes
Change Events for Fields
Sending Data Differences for Fields of Updated Records
Data Differences in Event Fields
How to Reconstruct a Field from Its Diff Value
Considerations for Newline Characters and Computing the SHA-256 Hash
Change Events for Custom Field Type Conversions
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Data Differences in Event Fields

When the updated text field value is sent as a diff, it contains the SHA-256 hash value and data differences in the unified diff format.
The field whose data is sent as a unified diff contains a value in this format.

Example

In a Pub/Sub API client, the field contains the unified diff value in this format.

And the fields whose values are sent as a unified diff are listed in diffFields in ChangeEventHeader.

In a Streaming API (CometD) client, the field contains the diff subfield, which contains the unified diff value.

This change event is received in a Pub/Sub API client after the Description field with more than 1,000 characters is updated for an account. The Description field contains the hash value after the +++ prefix followed by the data differences.

The updates made to the diff field are the following.

  • In the paragraph starting with “Business applications,” the word “applications” was replaced with “apps.”
  • In the paragraph starting with “As cloud computing grows,”, one sentence was appended at the end of the paragraph: “And keep in mind that if you have to buy and manage hardware and software, what you’re looking at isn’t really cloud computing but a false cloud.”

This event for the account creation shows the original and full values in the Description field before it was updated. If you generate the SHA-256 hash on the full value, you get the same value sent in the account update event (682b8747ccdb93b546e7bbe479b27d26ec7c38ccabb76cdd8308c6595492bffc).