Merge pull request #5531 from magento/dobooth-prefixes

Add warning about prefixes in generated whitelists.

Author: dobooth

guides/v2.3/extension-dev-guide/declarative-schema/migration-commands.md

@@ -107,6 +107,9 @@ Each CSV file contains a row that defines the column (or other database entity)
 
 Backward compatibility must be maintained. Therefore, declarative schema does not automatically delete database tables, columns or keys that are not defined in a `db_schema.xml` file. Declarative schema cannot delete these elements because these items can be declared somewhere else, such as in an `Setup/UpgradeSchema.php` file.
 
+{: .bs-callout-warning }
+Whitelists cannot be generated on Magento instances that use a database prefix. The presence of a prefix impacts the names of some DB entities, such as the names of keys, and these names cannot be used in generated whitelists. The whitelist should be generated by the extension developer on a development environment with no prefixes.
+
 The `<module_vendor>/<module_name>/etc/db_schema_whitelist.json` file provides a history of all tables, columns, and keys added with declarative schema. It is required to allow drop operations. It can be generated manually or created automatically with the following command:
 
 ```bash