hibernate/hibernate-orm · error · CoercionException

value must contain exactly one character: '" + string + "'

Error message

value must contain exactly one character: '" + string + "'

What it means

CharacterJavaType.fromString requires a CharSequence of length exactly 1; an empty string or a multi-character sequence throws CoercionException('value must contain exactly one character'). It is the parsing path used when a Character attribute is hydrated from string data.

Source

Thrown at hibernate-core/src/main/java/org/hibernate/type/descriptor/java/CharacterJavaType.java:38

	public CharacterJavaType() {
		super( Character.class );
	}

	@Override
	public boolean useObjectEqualsHashCode() {
		return true;
	}

	@Override
	public String toString(Character value) {
		return value.toString();
	}

	@Override
	public Character fromString(CharSequence string) {
		if ( string.length() != 1 ) {
			throw new CoercionException( "value must contain exactly one character: '" + string + "'" );
		}
		return string.charAt( 0 );
	}

	@Override
	public boolean isInstance(Object value) {
		return value instanceof Character;
	}

	@Override
	public Character cast(Object value) {
		return (Character) value;
	}

	@Override
	public <X> X unwrap(Character value, Class<X> type, WrapperOptions options) {
		if ( value == null ) {
			return null;

View on GitHub (pinned to fad1729dce)

Solutions

1. Use CHAR(1)/NCHAR(1) and make sure stored values are exactly one character.
2. Clean the data: UPDATE t SET c = SUBSTRING(c FROM 1 FOR 1) WHERE CHAR_LENGTH(c) <> 1, and handle empty rows explicitly.
3. Add a converter that trims and defaults empty input to a chosen character.

Example fix

-- before
UPDATE users SET initial = 'AB'; -- later hydrate throws CoercionException

-- after
UPDATE users SET initial = SUBSTRING(initial FROM 1 FOR 1) WHERE CHAR_LENGTH(initial) > 1;
DELETE-fallback or converter for '' rows:
@Converter
public class CharConverter implements AttributeConverter<Character, String> {
    public String convertToDatabaseColumn(Character c) { return c == null ? null : c.toString(); }
    public Character convertToEntityAttribute(String s) { return (s == null || s.isEmpty()) ? ' ' : s.trim().charAt(0); }
}

static boolean isSingleChar(String s) {
    return s != null && s.length() == 1;
}
// guard: if (!isSingleChar(col)) col = normalize(col); // trim or default

static Character toCharOrNull(String s) {
    if (s == null || s.isEmpty()) return null;
    String t = s.trim();
    return t.isEmpty() ? null : Character.valueOf(t.charAt(0));
}

When it happens

Trigger: A CHAR(n)/VARCHAR column feeding a Character attribute with values longer or shorter than one character; empty strings; string parameters bound to Character fields.

Common situations: DB CHAR columns whose padding survives the read (no trim) so values come back longer than 1; schema evolved from a wider string column without cleaning data; NOT NULL string columns defaulted to ''.

Related errors

• Cannot convert Character value '" + character + "' to Boolea
• value contains more than one character: '" + string + "'
• The INSERT statement for table [%s] contains no column, and
• cannot recreate collection while filter is enabled: " + coll
• cannot recreate collection while filter is enabled [%s : %s]

AI-assisted analysis of hibernate/hibernate-orm@fad1729dce (2026-08-22). Data as JSON: /api/errors/5fc29037a42be019. Report an issue: GitHub.