Error Handling

FMDataException

When the FileMaker Data API returns an error, FMData throws an FMDataException:

try
{
    var results = await client.FindAsync(query);
}
catch (FMDataException ex)
{
    Console.WriteLine($"FileMaker error {ex.FMErrorCode}: {ex.FMErrorMessage}");
}

FMDataException extends System.Exception and adds:

Property	Type	Description
`FMErrorCode`	`int`	The FileMaker error code
`FMErrorMessage`	`string`	Human-readable description of the error

Common Error Codes

Code	Meaning
0	No error (success)
102	Field is missing
105	Layout is missing
106	Table is missing
401	No records match the request
500	Date value does not meet validation
802	Unable to open the file
952	Invalid FileMaker Data API token

FMData includes a comprehensive dictionary of all FileMaker error codes (0–1715) and their descriptions.

How FMData Maps HTTP Responses

The FileMaker Data API returns standard HTTP status codes, but uses 500 Internal Server Error for many application-level errors. FMData handles these cases:

Find Operations

HTTP Status	FileMaker Code	FMData Behavior
200 OK	—	Returns results normally
404 Not Found	—	Returns an empty collection
500 Internal Server Error	401	Returns an empty collection (no records found)
500 Internal Server Error	Other	Throws `FMDataException` with code and message

GetByFileMakerIdAsync

HTTP Status	FileMaker Code	FMData Behavior
200 OK	—	Returns the record
404 Not Found	—	Returns `null`
500 Internal Server Error	401	Returns `null`
500 Internal Server Error	Other	Throws `FMDataException` with code and message

Create and Edit Operations

HTTP Status	FMData Behavior
200 OK	Returns the response
404 Not Found	Returns response with `"404"` error code (edit only)
500 Internal Server Error	Throws `FMDataException` with code and message

Delete Operations

HTTP Status	FMData Behavior
200 OK	Returns the response
404 Not Found	Returns response with `"404"` code and `"Error"` message
500 Internal Server Error	Throws `FMDataException` with code and message

Authentication Errors

FMData automatically retries requests that receive a 401 Unauthorized HTTP response by refreshing the authentication token. This handles expired Data API tokens transparently.