TAppError / EAppError

Declared in: UErrorCodes

TAppError is a value type (record) that carries a structured error: an EC_* code, a human-readable message, and optionally a native engine error number and message from MySQL/MariaDB or ElevateDB.
It is the type of the LastError property on TMMScript, TMMUpdater, and TMMHttpClient.

A default-initialised TAppError (Code = 0 = EC_NONE) represents the absence of an error.
Use IsError rather than comparing Code to zero directly.

TAppError

TAppError = record
  Code      : Integer;  // EC_* error code; 0 (EC_NONE) = no error
  Msg       : string;   // human-readable description; '' = no error
  NativeCode: Integer;  // raw engine error number; 0 = not applicable
  NativeMsg : string;   // raw engine error message; '' = not applicable

  function IsError: Boolean;

  // Internal constructors (used by the library):
  class function Make(...): TAppError; static;
  class function MakeFmt(...): TAppError; static;
  class function FromException(...): TAppError; static;
end;

Fields

Field	Description
`Code`	`EC_*` error code. `0` = `EC_NONE` = no error.
`Msg`	Human-readable description. Empty when `Code = EC_NONE`.
`NativeCode`	Raw MySQL or EDB engine error number when a server-side or engine error is the root cause — the `/N<number>` suffix shown in the application log. `0` when not applicable.
`NativeMsg`	Original engine error message from the PDO or EDB driver. Empty when not applicable.

IsError

function IsError: Boolean;

Returns True when Code <> EC_NONE. Prefer this over comparing Code to zero directly, since EC_NONE = 0 may not be obvious to future readers.

Make / MakeFmt / FromException

These constructors are used internally by the library to build TAppError values. You do not normally need to call them directly.

Make builds a TAppError from an explicit code and message string. MakeFmt applies Args to the standard EM_* message template for ACode. FromException builds from a caught exception, setting Msg to E.Message.

EAppError

EAppError is an exception class that wraps a TAppError. It is raised when a structured error must propagate across call boundaries. Exception.Message mirrors Error.Msg.

EAppError = class(Exception)
  constructor Create(const AError: TAppError); overload;
  constructor CreateCode(ACode: Integer; const AMsg: string;
    ANativeCode: Integer = 0; const ANativeMsg: string = ''); overload;
  property Error: TAppError read FError;
end;

EAppError is not raised by TMMScript.Execute or TMMUpdater.Execute — those report errors through Success, LastError.Msg, and LastError properties. It may be raised by lower-level operations inside the pipeline. Catch it when you call lower-level entry points directly, or let it propagate and handle it at a higher level.

try
  Script.Execute;
except
  on E: EAppError do
    ShowMessage(Format('[E%d] %s', [E.Error.Code, E.Error.Msg]));
end;

Using UErrorCodes

TAppError is visible through EDBMMClient without an explicit uses entry. Add UErrorCodes only when your code compares LastError.Code against EC_* constants directly:

uses EDBMMClient, UErrorCodes;  // UErrorCodes needed for EC_* constants

Script.Execute;
if Script.LastError.IsError then
begin
  if Script.LastError.Code = EC_HTTP_TIMEOUT then
    ShowMessage('Query timed out — add a LIMIT clause or increase server timeouts')
  else
    ShowMessage(Script.LastError.Msg);
end;