# Default to when missing **URL:** \ **Category:** Ruby\ **Created:** [February 6, 2007, 11:50pm UTC](https://www.ruby-forum.com/t/default-to-when-missing/84684 "2007-02-06T23:50:27Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![jerryjj](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9d8465/32.png) [@jerryjj](https://www.ruby-forum.com/u/jerryjj)\ **Post date:** [February 6, 2007, 11:50pm UTC](https://www.ruby-forum.com/t/default-to-when-missing/84684/1 "2007-02-06T23:50:27Z")
On my website, I have a field in the sql server that lists the image location/name to display for an item. All is wonderful. How can I have the site select an ‘image is no available’ image if the file name it is looking for does not exist? Right now, it is just showing the alternate text, which is the image file name it is looking for. Would it be a big hit on performance to have it check the images dir for the file name prior to rendering the page, or should it keep an index somewhere of the files that are there, or am I complete off base in how to approach this? ---
**Author:** ![jerryjj](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9d8465/32.png) [@jerryjj](https://www.ruby-forum.com/u/jerryjj)\ **Post date:** [February 7, 2007, 12:01am UTC](https://www.ruby-forum.com/t/default-to-when-missing/84684/2 "2007-02-07T00:01:27Z")
On Wed, Feb 07, 2007 at 07:49:20AM +0900, Jerry J. wrote: > On my website, I have a field in the sql server that lists the image > location/name to display for an item. All is wonderful. How can I have > the site select an ‘image is no available’ image if the file name it > is looking for does not exist? By configuring your webserver appropriately. You don’t even mention what webserver you use, so you’re not going to get a more specific answer than that here. However, as an example, if you are running Apache httpd then you can ask this question on the Apache httpd mailing list. > Right now, it is just showing the > alternate text, which is the image file name it is looking for. > Would it be a big hit on performance to have it check the images dir > for the file name prior to rendering the page Web servers don’t render pages - web browsers do. Web servers response to HTTP requests, and send back the HTML for the page. What the browser does with it is its own responsibility. If the HTML contains a reference to an image, a separate HTTP request is made by the browser to retrieve the image. If the image doesn’t exist (web server returns 404 Not Found) then it’s up to the browser what to do next. Many display a “broken image” icon. Brian. ---
**Author:** ![jerryjj](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9d8465/32.png) [@jerryjj](https://www.ruby-forum.com/u/jerryjj)\ **Post date:** [February 7, 2007, 3:01am UTC](https://www.ruby-forum.com/t/default-to-when-missing/84684/3 "2007-02-07T03:01:39Z")
I understand that browsers render the page, I could have worded that better. What I was meaning was when a request is sent, would it be a serious hit on performance to check for the image file, and if not present, default to the ‘no image available’ image. Or would it be best to have an index of the image file names and when a request is sent to the server, it checks the index, and if the image file is not listed, default to the ‘no image available’ image. At the moment, I am running Webrick. I am trying to get IIS to work with RoR. ---
**Author:** ![jerryjj](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9d8465/32.png) [@jerryjj](https://www.ruby-forum.com/u/jerryjj)\ **Post date:** [February 7, 2007, 9:41am UTC](https://www.ruby-forum.com/t/default-to-when-missing/84684/4 "2007-02-07T09:41:04Z")
On Wed, Feb 07, 2007 at 11:00:38AM +0900, Jerry J. wrote: > I understand that browsers render the page, I could have worded that > better. What I was meaning was when a request is sent, would it be a > serious hit on performance to check for the image file, and if not > present, default to the ‘no image available’ image. You mean: when the webserver gets a request for /images/foo.png, and foo.png does not exist, it returns a default image instead? Yes this is possible. Under Apache you would use mod\_rewrite, using the -f test to check if a file exists. > Or would it be > best to have an index of the image file names and when a request is > sent to the server, it checks the index, and if the image file is not > listed, default to the ‘no image available’ image. I think you are talking about testing the existence of a file in the filesystem, versus testing the existence of a key in a hash. The hash lookup will be a bit faster, but I don’t think you’ll see much difference in practice; if lots of clients are accessing non-existent files, then the directory will be cached by the O/S anyway. > At the moment, I am running Webrick. Then I guess you can serve /images/ from a small piece of Ruby which implements either of the above strategies. > I am trying to get IIS to work with RoR. No idea how you would do this with IIS, apart from continuing to map /images/\* to a piece of Ruby. ---
**Author:** ![jerryjj](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9d8465/32.png) [@jerryjj](https://www.ruby-forum.com/u/jerryjj)\ **Post date:** [February 7, 2007, 3:37pm UTC](https://www.ruby-forum.com/t/default-to-when-missing/84684/5 "2007-02-07T15:37:48Z")
On Tue, 06 Feb 2007 23:49:20 +0100, Jerry J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Right now, it is just showing the > alternate text, which is the image file name it is looking for. > Would it be a big hit on performance to have it check the images dir > for the file name prior to rendering the page, or should it keep an > index somewhere of the files that are there, or am I complete off base > in how to approach this? An index will probably flat-out outperform a system call on access, with the cost being in recomputation of said. However, benchmark. A few stat()s per request probably won’t be a bottleneck anyway. David V.