Merge pull request #151 from fukamachi/do-for-dao

Rename `do-cursor` -> `do-select`, and make it work in all RDBMS

README.markdown

@@ -608,6 +608,24 @@ Since `insert-dao`, `update-dao` and `delete-dao` are defined as generic functio
 ;=> #<USER {100835FB33}>
 ```
 
+### Iteration (Experimental)
+
+`do-select` is a macro to iterate over results from SELECT one by one. It's the same as `cl:loop`, but it uses CURSOR for PostgreSQL, which can reduce memory usage since it won't load whole results on memory.
+
+```common-lisp
+(do-select (dao (select-dao 'user
+ (where (:< "2024-07-01" :created_at))))
+ ;; Can be a more complex condition
+ (when (equal (user-name dao) "Eitaro")
+ (return dao)))
+
+;; Same but without using CURSOR
+(loop for dao in (select-dao 'user
+ (where (:< "2024-07-01" :created_at)))
+ when (equal (user-name dao) "Eitaro")
+ do (return dao))
+```
+
 ## Installation
 
 ```common-lisp

src/core/dao.lisp

@@ -62,7 +62,7 @@
  #:recreate-table
  #:ensure-table-exists
  #:deftable
- #:do-cursor))
+ #:do-select))
 (in-package #:mito.dao)
 
 (defun foreign-value (obj slot)
@@ -453,16 +453,28 @@
  `((:conc-name ,(intern (format nil "~@:(~A-~)" name) (symbol-package name)))))
  ,@options))
 
-(defmacro do-cursor ((dao select &optional index) &body body)
- (with-gensyms (main cursor)
- `(flet ((,main ()
- (let* ((*want-cursor* t)
- (,cursor ,select))
- (loop ,@(and index `(for ,index from 0))
- for ,dao = (fetch-dao-from-cursor ,cursor)
- while ,dao
- do (progn ,@body)))))
- (if (dbi:in-transaction *connection*)
- (,main)
- (dbi:with-transaction *connection*
- (,main))))))
+(defmacro do-select ((dao select &optional index) &body body)
+ (with-gensyms (main main-body select-fn cursor i)
+ `(block nil
+ (labels ((,main-body (,dao ,(or index i))
+ ,@(and (not index)
+ `((declare (ignore ,i))))
+ ,@body)
+ (,select-fn () ,select)
+ (,main ()
+ (case (dbi:connection-driver-type *connection*)
+ (:postgres
+ (let ((,cursor (let ((*want-cursor* t))
+ (,select-fn))))
+ (loop ,@(and index `(for ,i from 0))
+ for ,dao = (fetch-dao-from-cursor ,cursor)
+ while ,dao
+ do (,main-body ,dao ,i))))
+ (otherwise
+ (loop ,@(and index `(for ,i from 0))
+ for ,dao in (,select-fn)
+ do (,main-body ,dao ,i))))))
+ (if (dbi:in-transaction *connection*)
+ (,main)
+ (dbi:with-transaction *connection*
+ (,main)))))))

t/dao.lisp

@@ -270,8 +270,8 @@
  (ok (null (mito.dao::fetch-dao-from-cursor cursor)))))
 
  (let ((records '()))
- (do-cursor (dao (mito.dao:select-dao 'user) i)
- (push (cons i dao) records)
+ (do-select (user (mito.dao:select-dao 'user) i)
+ (push (cons i user) records)
  (when (<= 1 i)
  (return)))
  (ok (= (length records) 2))