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9.1 Custom functions

A custom Udf exposes application capabilities to DataQL, such as lookups, service calls and data conversion. Scripts call it by its registered name.

Implement the function​

Implement call(Hints, UdfParams) and read script arguments through allParams(). This function accepts one string and returns a greeting.

GreetingUdf.java
package com.example.dataway;

import net.hasor.dataql.domain.Hints;
import net.hasor.dataql.domain.Udf;
import net.hasor.dataql.domain.UdfParams;

public class GreetingUdf implements Udf {
    @Override
    public Object call(Hints hints, UdfParams params) {
        Object[] arguments = params.allParams();
        if (arguments.length != 1 || !(arguments[0] instanceof String name)) {
            throw new IllegalArgumentException("greeting requires one string argument");
        }
        return "Hello " + name;
    }
}

Register the function​

config is the application’s DatawayConfig; apply these settings before creating Dataway.

import com.example.dataway.GreetingUdf;

config.function("greeting", new GreetingUdf());

Call from a script​

return greeting('Dataway');

Returns "Hello Dataway"; the selected result handler produces the final response.

Usage notes​

Hints exposes execution options; UdfParams holds positional arguments. Return DataQL-supported values such as strings, numbers and collections. For binary values, see Result responses.

The registered instance can serve multiple queries. Keep request state out of instance fields. Use function libraries to group functions under a namespace.

Read execution context​

Applications can pass objects to a UDF through Hints. Read them in call with hints.getHint("app.context"); see Core APIs: Hints for configuration. UDFs receive read-only Hint entries, while contained objects retain their original references and may be shared.

Dataway uses DATAWAY_REQUEST and DATAWAY_RESPONSE for the current request and response, removing them after execution. Use distinct application Hint names. For script-level Header and Cookie operations, see Web functions.