What causes "no unique value" in hibernate/hibernate-orm?

Call isMultiValued() or check getValues().size() before getValue(), or just use getValues() when multiple values are legal.

hibernate/hibernate-orm · error · IllegalStateException

no unique value

Error message

no unique value

What it means

MetaAttribute#getValue throws IllegalStateException when the attribute holds zero or more than one value - only a single-valued meta attribute has a unique value. Meta attributes come from hbm <meta value="..."> elements and may legitimately repeat, so asking for 'the' value is only valid when exactly one exists.

Source

Thrown at hibernate-core/src/main/java/org/hibernate/mapping/MetaAttribute.java:38

	public MetaAttribute(String name) {
		this.name = name;
	}

	public String getName() {
		return name;
	}

	public java.util.List<String> getValues() {
		return Collections.unmodifiableList(values);
	}

	public void addValue(String value) {
		values.add(value);
	}

	public String getValue() {
		if ( values.size()!=1 ) {
			throw new IllegalStateException("no unique value");
		}
		return values.get(0);
	}

	public boolean isMultiValued() {
		return values.size()>1;
	}

	public String toString() {
		return "[" + name + "=" + values + "]";
	}
}

View on GitHub (pinned to fad1729dce)

Solutions

Call isMultiValued() or check getValues().size() before getValue(), or just use getValues() when multiple values are legal.
Deduplicate the <meta> elements in the hbm file so the attribute is single-valued.
Update tooling that assumes uniqueness to handle the value list.

Example fix

// before
String v = metaAttribute.getValue(); // throws when 0 or 2+ values

// after
if (metaAttribute.getValues().size() == 1) {
    String v = metaAttribute.getValue();
} else {
    List<String> all = metaAttribute.getValues();
}

Defensive patterns

Strategy: type-guard

Type guard

static Optional<String> uniqueValue(MetaAttribute attr) {
    return attr.getValues().size() == 1
            ? Optional.of(attr.getValue())
            : Optional.empty();
}

Prevention

Prefer getValues() over getValue() unless the mapping schema guarantees exactly one value.
Validate hbm files for duplicate <meta> elements with the same attribute name.
When merging inherited meta attributes, concatenate values instead of assuming uniqueness.

When it happens

Trigger: The same <meta attribute="..."> declared multiple times in one mapping element; inheritable meta attributes duplicated across mapping levels; tooling (hbm2java, reverse engineering) reading a single value from a multi-valued attribute; calling getValue() without checking the value count.

Common situations: Hand-edited hbm files where meta tags were duplicated by copy-paste; templates emitting the same meta attribute more than once; merging mappings that each carry the same meta attribute.

Related errors

AI-assisted analysis of hibernate/hibernate-orm@fad1729dce (2026-08-22). Data as JSON: /api/errors/b36d37ae07d85dfe. Report an issue: GitHub.