What causes "No wrapper for " in prestodb/presto?

Unwrap only to interfaces PrestoResultSetMetaData actually implements (e.g. java.sql.ResultSetMetaData) or the concrete PrestoResultSetMetaData class

prestodb/presto · error · SQLException

No wrapper for

Error message

No wrapper for

What it means

Standard JDBC Wrapper.unwrap() implementation: if isWrapperFor(iface) says this object does not implement or wrap the requested interface, the SQLException 'No wrapper for <iface>' is thrown. It means the caller requested a type this PrestoResultSetMetaData cannot expose.

Source

Thrown at presto-jdbc/src/main/java/com/facebook/presto/jdbc/PrestoResultSetMetaData.java:244

            case Types.BLOB:
                return Blob.class.getName();
            case Types.CLOB:
                return Clob.class.getName();
            case Types.ARRAY:
                return Array.class.getName();
        }
        return String.class.getName();
    }

    @SuppressWarnings("unchecked")
    @Override
    public <T> T unwrap(Class<T> iface)
            throws SQLException
    {
        if (isWrapperFor(iface)) {
            return (T) this;
        }
        throw new SQLException("No wrapper for " + iface);
    }

    @Override
    public boolean isWrapperFor(Class<?> iface)
            throws SQLException
    {
        return iface.isInstance(this);
    }

    private ColumnInfo column(int column)
            throws SQLException
    {
        if ((column <= 0) || (column > columnInfo.size())) {
            throw new SQLException("Invalid column index: " + column);
        }
        return columnInfo.get(column - 1);
    }
}

View on GitHub (pinned to 55bb57d202)

Solutions

Unwrap only to interfaces PrestoResultSetMetaData actually implements (e.g. java.sql.ResultSetMetaData) or the concrete PrestoResultSetMetaData class
Guard with isWrapperFor(iface) before calling unwrap
Use the JDBC-standard interfaces instead of vendor-specific types

Example fix

// before
MyVendorMeta m = meta.unwrap(MyVendorMeta.class); // throws
// after
if (meta.isWrapperFor(PrestoResultSetMetaData.class)) {
    PrestoResultSetMetaData m = meta.unwrap(PrestoResultSetMetaData.class);
}

Defensive patterns

Strategy: validation

Validate before calling

if (!meta.isWrapperFor(TargetType.class)) {
    throw new IllegalStateException("Metadata does not wrap " + TargetType.class.getName());
}

Type guard

boolean usable = iface != null && (iface.isInstance(meta));

Try / catch

try {
    T t = meta.unwrap(TargetType.class);
} catch (SQLException e) {
    if (e.getMessage() != null && e.getMessage().startsWith("No wrapper for")) {
        // use the standard java.sql.ResultSetMetaData interface instead
    } else { throw e; }
}

Prevention

Only unwrap to interfaces the object actually implements
Always call isWrapperFor before unwrap
Avoid vendor-specific wrapper types when writing driver-agnostic code

When it happens

Trigger: Calling metaData.unwrap(SomeClass.class) where SomeClass is not PrestoResultSetMetaData, not an interface it implements (ResultSetMetaData, Wrapper), and not assignable from the object.

Common situations: Unwrapping to a vendor-specific interface of a different driver (e.g. casting to another JDBC product's class); reflection-based framework code assuming a specific wrapper type; copy-pasted unwrap calls targeting the wrong driver's API class.

Related errors

AI-assisted analysis of prestodb/presto@55bb57d202 (2026-09-04). Data as JSON: /api/errors/7c3d162fb99ac92c. Report an issue: GitHub.