Emit events while parsing

[labs20]

Hi.

It would be very helpful if events were emitted while the parser is working, like "onColumn(col, sqlObj)", "onSubSelect(subSql, parentNode)", etc...

One could then implement validation and transform routines on the fly, while the targets are founding by the parser, instead of having to traverse the parser result afterwards.

Thanks!

[oguimbal]

IMO this is equivalent to an AST visitor, which is more flexible and simpler to implement (if you dont know it already, check out "visitor pattern" on google).

Example base class implementation here, and an example on how to use it here (not specific to the AST generated by node-sql-parser, though). Make it able transform things on the fly is quite easy. Exemple of what visitMember would look like:

 visitMember(val: ExprMember) {
        return { type: 'member', member: val.member, operand: this.visit(val.operand) }
}

Transofrming a ref would be quite easy doing so:

const transformedAst = new (class extends AstVisitor {
          visitRef(val: ExprRef) {
                 if (some condition)  return whatever;
                 return val;
         }).visit(myAst);