[CAY-2512] Support for custom functions in Expression API and Property API

• Type: Task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.2.M1
• Component/s: Core Library
• Assignee: Nikita Timofeev
• Reporter: Nikita Timofeev
• Created: 16/Jan/19 08:52
• Updated: 17/Jan/19 14:12
• Resolved: 16/Jan/19 14:23

Description

Cayenne supports SQL functions since 4.0 but only a limited set common for all supported DBs.
There are a lot more SQL functions provided by each DB that can't be supported by Cayenne directly. So we need a way to allow calls to this functions for users.

For the Property API it can be implemented as

<T> function(String functionName, Class<T> resultType, Object... arguments) {
   // ...
}

For the Expressions API we can use syntax like this:

Expression exp = exp("fn('SQL_FUNCTION', db:some.path, 123)")

This will cover almost all use cases with the exception of SQL functions with special syntax, like

OVERLAY ( 'foo bar' PLACING 'baz' FROM 5 )

Issue Links

• causes: CAY-2515 In-memory evaluation of user-defined SQL functions
• causes: CAY-2516 Support for custom syntax for SQL function call