private ClassMetadata singleClassConstraint() { if (requiresSort()) { return null; } QConClass clazzconstr = classConstraint(); if (clazzconstr == null) { return null; } ClassMetadata clazz = clazzconstr._classMetadata; if (clazz == null) { return null; } if (clazzconstr.hasChildren() || clazz.isArray()) { return null; } return clazz; }