Exceptions

Core Exceptions

Unit: Trysil.Exceptions

ETException

Base exception for all Trysil errors.

raise ETException.Create('Something went wrong');
raise ETException.CreateFmt('Entity %d not found', [LId]);

Property	Type	Description
Message	String	Error message (inherited from Exception)
NestedException	Exception	The exception that was active when this one was raised

NestedException captures the current exception object (via AcquireExceptionObject) at construction time. This enables exception chaining — when a Trysil exception is raised inside an except block, the original exception is preserved and accessible.

ETValidationException

Raised when entity validation fails. Extends ETException.

try
  LContext.Insert<TPerson>(LPerson);
except
  on E: ETValidationException do
    ShowMessage(E.Message);
end;

Validation errors are collected in TTValidationErrors before being raised as this exception.

ETConcurrentUpdateException

Raised when an optimistic locking conflict is detected — the record's version in the database does not match the version in the entity (another transaction modified it).

try
  LContext.Update<TPerson>(LPerson);
except
  on E: ETConcurrentUpdateException do
  begin
    // Refresh and retry, or notify the user
    LContext.Refresh<TPerson>(LPerson);
    ShowMessage('Record was modified by another user.');
  end;
end;

ETDataIntegrityException

Raised when a referential integrity constraint is violated — typically when deleting an entity that has dependent child records (with TRelation cascade set to False).

try
  LContext.Delete<TCompany>(LCompany);
except
  on E: ETDataIntegrityException do
    ShowMessage('Cannot delete: company has employees.');
end;

---

HTTP Exceptions

Unit: Trysil.Http.Exceptions

ETHttpServerException

Internal server infrastructure exception. Extends ETException.

ETHttpException

Base class for HTTP-specific exceptions with a status code.

raise ETHttpException.Create(409, 'Conflict detected');
raise ETHttpException.CreateFmt(422, 'Invalid field: %s', ['email']);

Property	Type	Description
StatusCode	Integer	HTTP status code
Message	String	Error message

ToJSon

Returns a structured JSON error response:

var LJson := LException.ToJSon;
// {"status":404,"message":"Person not found"}

If a NestedException exists, it is included:

{
  "status": 404,
  "message": "Person not found",
  "nestedException": {
    "status": 500,
    "message": "Original error details"
  }
}

Convenience Subclasses

Exception	Status Code	Usage
ETHttpBadRequest	400	Invalid request data
ETHttpUnauthorized	401	Authentication required or failed
ETHttpForbidden	403	Authenticated but insufficient permissions
ETHttpNotFound	404	Resource not found
ETHttpMethodNotAllowed	405	HTTP method not supported for this endpoint
ETHttpInternalServerError	500	Unexpected server error

All subclasses have simplified constructors (no status code parameter):

// In a controller method
raise ETHttpNotFound.Create('Person not found');
raise ETHttpNotFound.CreateFmt('Person %d not found', [AID]);

raise ETHttpBadRequest.Create('Missing required field: name');
raise ETHttpForbidden.Create('Insufficient permissions');
raise ETHttpUnauthorized.Create('Invalid token');

TExceptionHelper

A class helper on Exception that adds ToJSon to any exception:

try
  // ...
except
  on E: Exception do
    LResponse.Content := E.ToJSon;
end;

This produces {"status":500,"message":"..."} for any exception, with nested exception support for ETException descendants.

---

Exception Hierarchy

Exception
└── ETException
    ├── ETValidationException
    ├── ETConcurrentUpdateException
    ├── ETDataIntegrityException
    └── ETHttpServerException
    └── ETHttpException
        ├── ETHttpBadRequest (400)
        ├── ETHttpUnauthorized (401)
        ├── ETHttpForbidden (403)
        ├── ETHttpNotFound (404)
        ├── ETHttpMethodNotAllowed (405)
        └── ETHttpInternalServerError (500)

Best Practices

1. Catch specific exceptions — handle ETValidationException and ETConcurrentUpdateException explicitly rather than catching the generic ETException

2. Use HTTP exceptions in controllers — the HTTP server automatically converts them to the appropriate HTTP response with status code and JSON body

3. Check NestedException — when debugging, inspect NestedException for the root cause of chained errors

4. Refresh after concurrent update — when catching ETConcurrentUpdateException, call Refresh<T> to reload the entity with the latest database state before retrying