Custom Rules

Implement Rule when the built-in rules do not describe your domain.

import dev.ditsche.teki.rule.Rule;
import dev.ditsche.teki.rule.RuleResult;

public class StartsWithRule implements Rule {
    private final String prefix;

    public StartsWithRule(String prefix) {
        this.prefix = prefix;
    }

    @Override
    public RuleResult test(Object value) {
        if (value == null) return RuleResult.resolve();
        return RuleResult.passes(value.toString().startsWith(prefix));
    }

    @Override
    public String message(String field) {
        return field + " must start with " + prefix;
    }

    @Override
    public String getType() {
        return "starts_with";
    }
}

Attach the rule with custom(...):

import dev.ditsche.teki.Teki;

import static dev.ditsche.teki.rule.builder.Rules.*;

Teki schema = Teki.fromRules(
    string("ticketId").required().custom(new StartsWithRule("TKT-"))
);

Rule results

Use the helpers on RuleResult to describe the outcome:

Helper	Use it when
`RuleResult.passes(boolean)`	The rule only accepts or rejects
`RuleResult.resolve()`	The value is valid and unchanged
`RuleResult.resolve(value)`	The value is valid and should be written back
`RuleResult.reject()`	The value is invalid

Normalizing in custom rules

Rules can transform values by returning RuleResult.resolve(newValue).

public RuleResult test(Object value) {
    if (value instanceof String text) {
        return RuleResult.resolve(text.strip().toLowerCase());
    }

    return RuleResult.resolve();
}

When Teki sees a changed result, it writes the new value back to the validated field.

Custom Rules

Rule results

Normalizing in custom rules

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