Grabbing next id before saving to the db?

[crazeinc]

I'd like to be able to grab the next primary key id (or maybe the last id used + 1) from a table so I can set an image name that corresponds with that id (and subsequent row information). Is there something that HibernateDaoSupport provides to do this?

[crazeinc]

This is the solution I've come up with so far. It works, but I'm sure it could be better. I'm doing this because I've been told to store the images in the file system and not the database. I think that storing the pictures by their picture id should make displaying them trivial and eliminate any funky naming problems. Of course I could be wrong, so I look forward to any comments.

        MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;
        CommonsMultipartFile file = (CommonsMultipartFile) multipartRequest.getFile("file");

        //all of this just to grab the image extension
        String name = file.getOriginalFilename();
        int extIndex;
        for&#40;extIndex=0;extIndex<name.length&#40;&#41;;extIndex++&#41;&#123;
        	if&#40;name.charAt&#40;extIndex&#41;=='.'&#41;&#123;
        		break;
        	&#125;
        &#125;
        String imageExt = name.substring&#40;extIndex&#41;;
        
        synchronized&#40;this&#41;&#123;
	        //make dummy picture
	        Picture blankPicture = new Picture&#40;&#41;;
	        blankPicture.setLocation&#40;"notset"&#41;;
	        pictureManager.savePicture&#40;blankPicture&#41;;
	        
	        //grab dummy picture and rename image
	        Picture picture = pictureManager.getPictureByLocation&#40;"notset"&#41;;
	        String picId = String.valueOf&#40;picture.getId&#40;&#41;&#41;;       
	        String uploadDir = getServletContext&#40;&#41;.getRealPath&#40;"/uploads"&#41; + "/" + picId + imageExt;
	        
	        //save real picture
	        picture.setId&#40;picture.getId&#40;&#41;&#41;;
	        picture.setLocation&#40;uploadDir&#41;;
	        pictureManager.savePicture&#40;picture&#41;;
	        
	        File dirPath = new File&#40;uploadDir&#41;;
	        InputStream stream = file.getInputStream&#40;&#41;;
	        OutputStream bos = new FileOutputStream&#40;uploadDir&#41;;
	        int bytesRead = 0;
	        byte&#91;&#93; buffer = new byte&#91;8192&#93;;
	
	        while &#40;&#40;bytesRead = stream.read&#40;buffer, 0, 8192&#41;&#41; != -1&#41; &#123;
	            bos.write&#40;buffer, 0, bytesRead&#41;;
	        &#125;
	        bos.close&#40;&#41;;
	        stream.close&#40;&#41;;
        &#125;

[Costin Leau]

In HB it depends a lot on the type of strategy you use for your id fields
when mapping each POJO. See file:///c:/work/study/hibernate-2.1.7/doc/reference/en/html_single/index.html#mapping-declaration-id

AFAIK HibernateDaoSupport doesn't support such a feature. In your case you can either work with an 'identity' id - you can keep the counter in a helper class and increment it yourself - however you have to make sure that no one else writes inside the table or your counter will be wrong.

Another alternative would be to use a HB interceptor to write again on PostFlush or (PreFlush) but I don't know if that will work as there are some restricition (like not being able to modify the information that is going to be written).

Ofc, you can always work with assign keys or write the information twice - first to get the id, second time to update the name field.

[Costin Leau]

Don't forget to take this problem with the HB forums (do a search first). For sure you'll find there some good solutions to this problem.

[irbouho]

PJ,
Let's refactor this code a little bit; the picture path is : getServletContext().getRealPath("/uploads") + id + ext:

1. getServletContext().getRealPath("/uploads"):
First of all, getServletContext().getRealPath("/uploads") is quite constant. So you can take it out, and inject it using Spring IoC. If this value, really, really does not change, there should be no need to save it any more in the database.

2. id:
id is, I guess, the primary key for the images table. So let just take it out from the image path column.

3. ext:
well, we have to keep this data, and perhaps just rename the table column to extention.

Solution:
now we can solve the initial "problem" as follows:
1. save the picture row into the database and get the id returned by hibernate
2. build the picture path: constant injected by Spring + id + extension
3. save the uploaded file to the disk

transactions you can refactor your code a bit to wrap 1., 2. and 3. in the same transaction. That way, if 3. fails, 1. will be rolled back.
HTH