Field-Level Calculations, Constants, and Validations

User-defined functions at the field level are the ultimate in flexibility and power for a database, but this degree of flexibility is not possible in the ODBC driver. To provide this level of functionality, the file format would have to be changed to tell the ODBC driver where to find the necessary code fragment being used for the calculation and the entire Superbase language parser would have to be added to the driver. Also, the user-defined function may depend on other functions being present, or on global variables having been defined and initialised by the user's program. At some point it would cease to be an engine and merely be most of Superbase. As such, some limitations had to be placed on what the Superbase ODBC driver could reasonably support at the field level.

Validations are also supported, but only those which are of the simplest variety. Something like:

MyField.MYFILE > 255

will also work in the driver, but crossfile lookup validations which include the REQUEST keyword are not supported and if present will result in the file being opened read-only. If you need to write to the file, do not put validations which use the REQUEST keyword in the field description, put them into your code. Then put the same (modified as necessary for language, etc.) validations into the non-Superbase program which will also be writing to the file. If a file has validation, calculation, or constant formulae which use user-defined functions or unsupported SBL key words, or references files in those validations, calculations, or constants which are not already open, then the file will be opened in read-only mode, regardless of the mode requested.