MyCATApache/Mycat-Server · error · IllegalArgumentException

functionName is null

Error message

functionName is null

What it means

RuleConfig's constructor requires a non-null functionName — the name of the partition algorithm (function) that implements the sharding rule. If functionName is null, IllegalArgumentException("functionName is null") is thrown immediately, since a rule without an algorithm name is unusable.

Solutions

1. Add function="<algorithmName>" to the <rule> element in rule.xml.
2. Ensure the algorithm name matches a <function name=...> defined in rule.xml.
3. If constructing RuleConfig programmatically, pass a non-null function name string.

Example fix

// before (rule.xml)
<tableRule name="order-rule"><rule><columns>id</columns></rule></tableRule>
// after
<tableRule name="order-rule"><rule><columns>id</columns><function>mod-long</function></rule></tableRule>

if (functionName == null || functionName.isEmpty()) throw new IllegalArgumentException("rule function attribute required");

try { new RuleConfig(column, fn); } catch (IllegalArgumentException e) { if ("functionName is null".equals(e.getMessage())) { LOG.error("rule missing function attr"); } throw e; }

When it happens

Trigger: new RuleConfig(column, null) or rule.xml parsing where a tableRule's rule element has no function attribute (attribute resolves to null).

Common situations: rule.xml <rule> element missing the function attribute; programmatic rule construction omitting the function name; XML loader returning null for an empty attribute value.

Related errors

• name is null
• table name is null
• dataNode name is null
• ruleRequired but rule is null
• no rule column is found

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/d0a4fff9e4e5d0a0. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/config/model/rule/RuleConfig.java:41

 */
package io.mycat.config.model.rule;

import io.mycat.route.function.AbstractPartitionAlgorithm;

import java.io.Serializable;

/**
 * 分片规则，column是用于分片的数据库物理字段
 * @author mycat
 */
public class RuleConfig implements Serializable {
	private final String column;
	private final String functionName;
	private AbstractPartitionAlgorithm ruleAlgorithm;

	public RuleConfig(String column, String functionName) {
		if (functionName == null) {
			throw new IllegalArgumentException("functionName is null");
		}
		this.functionName = functionName;
		if (column == null || column.length() <= 0) {
			throw new IllegalArgumentException("no rule column is found");
		}
		this.column = column;
	}

	

	public AbstractPartitionAlgorithm getRuleAlgorithm() {
		return ruleAlgorithm;
	}



	public void setRuleAlgorithm(AbstractPartitionAlgorithm ruleAlgorithm) {
		this.ruleAlgorithm = ruleAlgorithm;

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