To handle a situation in Ory where some identities have only a username, some only an email, and some both, you need to design your identity schema so that both fields are optional, but at least one must be present. Ory supports marking both username and email as identifiers in the schema, but the schema itself must enforce the rule that at least one is required. The knowledge sources provide examples where both fields are present and marked as identifiers, but by default, the JSON Schema in these examples requires both fields (using the required array). To allow either field, you need to use JSON Schema's conditional validation (such as oneOf, anyOf, or similar constructs) to specify that at least one of the fields must be present. Here’s a conceptual example based on the patterns in the documentation:

json {   "$id": "<https://example.com/registration.schema.json>",   "$schema": "<http://json-schema.org/draft-07/schema#>",   "title": "Person",   "type": "object",   "properties": {     "traits": {       "type": "object",       "properties": {         "email": {           "type": "string",           "format": "email",           "<http://ory.sh/kratos|ory.sh/kratos>": {             "credentials": {               "password": {                 "identifier": true               }             }           }         },         "username": {           "type": "string",           "<http://ory.sh/kratos|ory.sh/kratos>": {             "credentials": {               "password": {                 "identifier": true               }             }           }         }       },       "anyOf": [         { "required": ["email"] },         { "required": ["username"] }       ],       "additionalProperties": false     }   } }

- This schema allows an identity to have only an email, only a username, or both. - Both fields are marked as identifiers, so either can be used to log in. - The anyOf keyword ensures that at least one of the fields is present. This approach is consistent with Ory’s support for multiple identifiers and flexible identity schemas, as described in the documentation and examples provided, though the exact use of anyOf is not shown in the docs, it is a standard JSON Schema feature and aligns with Ory’s schema validation approach [Customize identity schemas](https://www.ory.sh/docs/kratos/manage-identities/customize-identity-schema#multiple-identifiers). If you need more advanced validation (e.g., enforcing at least one of several fields), refer to the [advanced validation section](https://www.ory.sh/docs/kratos/manage-identities/customize-identity-schema#more-advanced-validation) for further JSON Schema techniques. Note: The knowledge sources do not provide a direct, copy-paste example of this exact scenario, but the approach above is derived from the documented schema flexibility and JSON Schema capabilities supported by Ory.