Use TSL to generate TSL strings?

[cben]

One drawback of exposing an API accepting a pseudo-SQL query strings (parsed by TSL) is that it's tricky for clients to generate those strings with correct value quoting... We have some ad-hoc string-building code and I'm looking at more principled generation from something like an AST. In Go.

• I first looked at squirrel but turns out it can't generate a self-contained SQL string. It only emits ? placeholders, and returns a separte array of values, assuming you have a DB interface that safely takes separate template + args.
  This is good design but our API doesn't support that 😁, it takes a single TSL string.

• So my next idea was using TSL itself to generate a TSL string! 💡
  Ironically, currently sql walker uses squirrel as well, emitting ? and separate values 😁

Is this something you'd like like TSL to support — round trip from AST to a TSL string that parses to same AST? 🎋 -> 🔤 -> 🎋

• Note that for sending SQL queries to actual databases, it may still be best to emit placeholders + separate values. Emphasis on plural databases — one of the reasons Go stdlib haven't implemented string quoting is that quoting rules differ by database 🤦
  This probably means having separate SQL and TSL walkers. Maybe some clever polymorphism with Sqlizer interface is possible, not sure how.

[yaacov]

Interesting 👍

are you suggesting a builder that will help building tsl-tree from code, instead of parsing tsl-phrases ?

e.g. something to automate this ?

right := Node{Func: StringOp, Left: "Moki"}
left := Node{Func: StringOp, Left: "Not Moki"}

tslTreeRoot := Node(Func: EqOp, Right: right, Left: left}

[cben]

I'm suggesting a walker [or a flag on existing sql walker] that from the example you give above, would build the self-contained string "Moki" = "Not Moki".
My understading is that currently it builds ? = ? plus the args "Moki", "Not Moki", right?

[yaacov]

My understading is that currently it builds ? = ? plus the args "Moki", "Not Moki", right?

yes,

so filing in the args in a string with '?' place holders sounds like for each arg do strings.Replace of ? ?

[cben]

Interestingly, squirrel.Expr may provide the infrastructure to "smuggle" literals into squirrel:
https://github.com/Masterminds/squirrel/blob/master/expr.go#L31-L82
If any of the args supports .ToSql(), it inlines the result in place of the ?.

[yaacov]

sql walker return Sqlizer so it should supports .ToSql() out of the box ... !?

[cben]

OTOH, I don't understand how this now works:

	case tsl.StringOp:
		s = sq.Expr(n.Left.(string))

Isn't sq.Expr() supposed to take an SQL fragment (with possible placeholders)? Here you're feeding it the string as-is?
Playing with the tests, but I'm not managing to break it the way I expected 👍, so I guess it's time to call it a night :)