Red Hat SummitChapter 11. User Defined Functions
11.1. User Defined Functions
Teiid Designer enables you to extend Teiid's function library by using custom or User Defined Functions(UDFs). You can define a UDF with follwing properties.
- Function Name - When you create the function name, remember that:
- You cannot overload existing Teiid System functions.
- The function name must be unique among user defined functions in its model for the number of arguments. You can use the same function name for different numbers of types of arguments. Hence, you can overload your user defined functions.
- The function name cannot contain the '.' character.
- The function name cannot exceed 255 characters.
- Input Parameters- Input Parameter defines a type specific signature list. All arguments are considered required.
- Return Type- the expected type of the returned scalar value.
- Pushdown - Indicates the expected pushdown behavior. It can be one of REQUIRED, NEVER, ALLOWED. If NEVER or ALLOWED are specified then a Java implementation of the function must be supplied. If REQUIRED is used, then user must extend the Translator for the source and add this function to its pushdown function library.
- invocationClass/invocationMethod- optional properties indicating the method to invoke when the UDF is not pushed down.
- Deterministic - if the method always returns the same result for the same input parameters. Defaults to false. It is important to mark the function as deterministic if it returns the same value for the same inputs as this leads to better performance.
Even Pushdown required functions need to be added as a UDF to allow Teiid to properly parse and resolve the function. Pushdown scalar functions differ from normal user defined functions in that no code is provided for evaluation in the engine. An exception is raised if a pushdown required function cannot be evaluated by the appropriate source.
