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improve Continue db code: use table-exists? instead of catch all exn?

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This commit is contained in:
Ryan Culpepper 2011-08-27 03:01:19 -06:00
parent a2f75e494d
commit 19774260f7
2 changed files with 8 additions and 5 deletions
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8
collects/web-server/scribblings/tutorial/continue.scrbl
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@ -975,7 +975,8 @@ following to the top of our model:
We will use the following bindings from the @racketmodname[db]
library: @racket[connection?], @racket[sqlite3-connect],
@racket[query-exec], @racket[query-list], and @racket[query-value].
@racket[table-exists?], @racket[query-exec], @racket[query-list], and
@racket[query-value].
The first thing we should do is decide on the relational structure of
our model. We will use the following tables:
@ -1011,7 +1012,7 @@ We can now write the code to initialize a @racket[blog] structure:
(define (initialize-blog! home)
(define db (sqlite3-connect #:database home #:mode 'create))
(define the-blog (blog db))
(with-handlers ([exn? void])
(unless (table-exists? db "posts")
(query-exec db
(string-append
"CREATE TABLE posts "
@ -1019,7 +1020,8 @@ We can now write the code to initialize a @racket[blog] structure:
(blog-insert-post!
the-blog "First Post" "This is my first post")
(blog-insert-post!
the-blog "Second Post" "This is another post")
the-blog "Second Post" "This is another post"))
(unless (table-exists? db "comments")
(query-exec db
"CREATE TABLE comments (pid INTEGER, content TEXT)")
(post-insert-comment!

5
collects/web-server/scribblings/tutorial/examples/model-3.rkt
View File

@ -14,7 +14,7 @@
(define (initialize-blog! home)
(define db (sqlite3-connect #:database home #:mode 'create))
(define the-blog (blog db))
(with-handlers ([exn? void])
(unless (table-exists? db "posts")
(query-exec db
(string-append
"CREATE TABLE posts "
@ -22,7 +22,8 @@
(blog-insert-post!
the-blog "First Post" "This is my first post")
(blog-insert-post!
the-blog "Second Post" "This is another post")
the-blog "Second Post" "This is another post"))
(unless (table-exists? db "comments")
(query-exec db
"CREATE TABLE comments (pid INTEGER, content TEXT)")
(post-insert-comment!