Naming Conventions and Annotations¶
The following naming conventions allow the definition of some custom functions without the need of Java annotations, even if it is recommended to use them. All the names used in the naming conventions are case sensitive.
To make a Java class to recognizable as a custom function without Java annotations, its name must match the following pattern:
- <FunctionName> + “ItpFunction”
This way, a Java class named Concat_SampleItpFunction will be interpreted as a function named Concat_Sample.
All Java methods implementing the function signatures must have the name execute. The signature associated with each method will be extracted from the Java method parameters. For example a class named Concat_SampleItpFunction with a method execute(valueA:String, valueB:String):String will generate the function signature CONCAT_SAMPLE(arg1:text, arg2:text).
To define a parameter with arity n in a custom function, the last parameter has to be an array. E.g., the class Concat_SampleItpFunction with a method declared as public String execute(String … inputs).
Custom functions which return type depends on the type of their input parameters or return an array or register, can define an additional method with equivalent signature to the one of execute. This additional method must be named executeReturnType. The definition of this method is optional. If it is not present, the execute method will be called and the return type will be obtained from the results of the execution. The advantage of defining the method executeReturnType is that in some cases calculating the return type is much less complex and time consuming than actually executing the function, thus by providing this method the performance is improved.
Naming conventions only cover a subset of all the possible custom
functions. In order to prevent the limitations using naming conventions
it is recommended to use the Java annotations provided by Denodo in the
com.denodo.common.custom.annotations.CustomElement. Class annotation used to define the class as a custom function. The annotation requires the parameters
name: name of the custom function.
type: In ITPilot it must be CustomElementType.ITPFUNCTION.
com.denodo.common.custom.annotations.CustomExecutor. Method annotation used to specify the method as a function signature. This method will be executed when using the function with the appropriate arguments. The annotation has an optional variable syntax in order to specify the syntax of the function signature when presenting it to the user at the Wrapper Generation Tool.
com.denodo.common.custom.annotations.CustomExecutorReturnType. Method annotation used to specify the method as the one used to compute the return type of a function signature before executing a query.
com.denodo.common.custom.annotations.CustomParam. Parameter annotation with the parameter name, used to make more user friendly the auto generated syntax description of the signature. If this annotation is not used, the syntax will use the names arg1, arg2, etc. to represent the input parameters.