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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] We will use the following bindings from the @racketmodname[db]
library: @racket[connection?], @racket[sqlite3-connect], 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 The first thing we should do is decide on the relational structure of
our model. We will use the following tables: 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 (initialize-blog! home)
(define db (sqlite3-connect #:database home #:mode 'create)) (define db (sqlite3-connect #:database home #:mode 'create))
(define the-blog (blog db)) (define the-blog (blog db))
(with-handlers ([exn? void]) (unless (table-exists? db "posts")
(query-exec db (query-exec db
(string-append (string-append
"CREATE TABLE posts " "CREATE TABLE posts "
@ -1019,7 +1020,8 @@ We can now write the code to initialize a @racket[blog] structure:
(blog-insert-post! (blog-insert-post!
the-blog "First Post" "This is my first post") the-blog "First Post" "This is my first post")
(blog-insert-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 (query-exec db
"CREATE TABLE comments (pid INTEGER, content TEXT)") "CREATE TABLE comments (pid INTEGER, content TEXT)")
(post-insert-comment! (post-insert-comment!

5
collects/web-server/scribblings/tutorial/examples/model-3.rkt
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@ -14,7 +14,7 @@
(define (initialize-blog! home) (define (initialize-blog! home)
(define db (sqlite3-connect #:database home #:mode 'create)) (define db (sqlite3-connect #:database home #:mode 'create))
(define the-blog (blog db)) (define the-blog (blog db))
(with-handlers ([exn? void]) (unless (table-exists? db "posts")
(query-exec db (query-exec db
(string-append (string-append
"CREATE TABLE posts " "CREATE TABLE posts "
@ -22,7 +22,8 @@
(blog-insert-post! (blog-insert-post!
the-blog "First Post" "This is my first post") the-blog "First Post" "This is my first post")
(blog-insert-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 (query-exec db
"CREATE TABLE comments (pid INTEGER, content TEXT)") "CREATE TABLE comments (pid INTEGER, content TEXT)")
(post-insert-comment! (post-insert-comment!