@Override
public Expression getAllowingNull(String attributeName) {
ObjectExpression exp = existingDerivedExpressionNamed(attributeName);
// The same (aliased) table cannot participate in a normal join and an outer join.
// To help enforce this, if the node already exists
if (exp != null) {
return exp;
}
ObjectExpression result = derivedExpressionNamed(attributeName);
result.doUseOuterJoin();
return result;
}
/** Defines a join between this expression and the target expression based on the ON clause. */
@Override
public Expression leftJoin(Expression target, Expression onClause) {
join(target, onClause);
((ObjectExpression) target).doUseOuterJoin();
return this;
}