- (with-slots (operator sub-expressions)
- expr
- (let ((subs (if (consp (car sub-expressions))
- (car sub-expressions)
- sub-expressions)))
- (write-char #\( *sql-stream*)
- (do ((sub subs (cdr sub)))
- ((null (cdr sub)) (output-sql (car sub) database))
- (output-sql (car sub) database)
- (write-char #\Space *sql-stream*)
- (output-sql operator database)
- (write-char #\Space *sql-stream*))
- (write-char #\) *sql-stream*)))
+ (with-slots (operator sub-expressions) expr
+ ;; we do this as two runs so as not to emit confusing superflous parentheses
+ ;; The first loop renders all the child outputs so that we can skip anding with
+ ;; empty output (which causes sql errors)
+ ;; the next loop simply emits each sub-expression with the appropriate number of
+ ;; parens and operators
+ (flet ((trim (sub)
+ (string-trim +whitespace-chars+
+ (with-output-to-string (*sql-stream*)
+ (output-sql sub database)))))
+ (let ((str-subs (loop for sub in sub-expressions
+ for str-sub = (trim sub)
+ when (and str-sub (> (length str-sub) 0))
+ collect str-sub)))
+ (case (length str-subs)
+ (0 nil)
+ (1 (write-string (first str-subs) *sql-stream*))
+ (t
+ (write-char #\( *sql-stream*)
+ (write-string (first str-subs) *sql-stream*)
+ (loop for str-sub in (rest str-subs)
+ do
+ (write-char #\Space *sql-stream*)
+ (output-sql operator database)
+ (write-char #\Space *sql-stream*)
+ (write-string str-sub *sql-stream*))
+ (write-char #\) *sql-stream*))
+ ))))