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Politics doesn't really effect us does it?

May 8th, 2012

Full transcript of the a television advertisement on the BBC for their coverage of politics, with the tag line: Everything is Politics. Making politics make sense..

Politics doesn’t really effect us does it? Oh, apart from the cost of our heating; and the fat content of our food; how often our streets are cleaned; the minimum wage, the maximum wage; cycle lanes, care homes, first homes, Sherlock Holmes, oh and the air we breathe. Yeh, apart from all that!

Hibernate exception - attempted to assign id from null one-to-one property

April 26th, 2012

I wrote this 3 years ago and never really got around to finishing it properly. I’m not doing this kind of work at the moment so there’s no incentive to complete it. I’m posting it now so that it might help others and to fulfil my 4 articles a month target!

This was a tricky one to solve! Tricky because the exception doesn’t happen at the point of error - it happens down the line at the time you try to commit a transaction. This is one of those error messages you just need to know. Here is the top of the exception’s stack trace. Almost all of the rest of the stack trace is inside hibernate and doesn’t give you any kind of clue as to the cause.

org.springframework.orm.hibernate3.HibernateSystemException:
attempted to assign id from null one-to-one property: clip; nested exception is org.hibernate.id.IdentifierGenerationException:
attempted to assign id from null one-to-one property: clip

The error message we are concerned with is:

attempted to assign id from null one-to-one property: clip

Where clip is the name of property. The exception is caused by trying to save a cascading object, without persisting the entity your object is referring to.

In my case I have the classes: Clip and Aaf. A Clip has one Aaf, so I need a one-to-one relationship. My Aaf object contains a blob but unfortunately hibernate doesn’t let you do lazy initialisations on one-to-one relationships, so I’ve had to use a Set even though there is only ever one entry.

The situation is made slightly more complicated by the fact that I’m using a UUID as my primary key. Hibernate doesn’t currently support UUID so I need a custom type along with a custom key generator.

XML

<class name="uk.co.bigsoft.bus.Aaf" table="aafs">
  <id name="id" type="uuid">
    <generator class="foreign">
      <param name="property">clip</param>
    </generator>
  </id>
  :
</class>

The Aaf’s hibernate ("hbm") file above says to use a uuid identifier that is generated from the primary key of the clip property. So if we look at the Aaf class you can see that the clip property has type Clip

Code

public class Aaf
  {
 
  private UUID id ;
  private Clip clip ;
  :

As you can see above id is the record identifier but clip (mentioned in the exception) is the relationship object that is used to set the record identifier. That is id is never explicitly set by us, we set the clip property.

The first example is *wrong*.

Code

Aaf aaf = new Aaf (aafInputStream);
aafs = new HashSet<aaf> ();
aafs.add (aaf);
clip.setAaf (aafs);

I was expecting that saving the Clip would do a cascade save on the Aaf object, but is doesn’t. We need the an intermediate step of persisting the Aaf object first. In order to do this we need to fill in all the details of the Aaf record.

Code

Aaf aaf = new Aaf (aafInputStream) ;
aaf.setClip (clip) ;
aafManager.set (aaf) ;
 
aafs = new HashSet<aaf> () ;
aafs.add (aaf) ;
clip.setAaf (aafs) ;
 
sc = new AafUpdateStatechange () ;
sc.setClipId (isaClip.getId ()) ;
remoteEventQueue.send (sc) ;

XML

<class name="uk.co.bigsoft.dino.bus.Aaf" table="aafs">
 
  <id name="id" type="dinouuid">
    <generator class="foreign">
      <param name="property">clip</param>
    </generator>
  </id>
 
  <many-to-one
    name="clip"
    column="id"
    insert="false"
    update="false"
    unique-key="true"
    class="uk.co.bigsoft.dino.bus.Clip"/>
 
  <property name="content" column="content" type="uk.co.bigsoft.dino.db.types.BlobUserType"/>
        
</class>

We need to persist Aaf object, before saving the clip relationship.

It's simple you can just merge main\LATEST into your private branch...

April 24th, 2012

Everyone keeps saying “It’s simple you can just merge [Clearcase] main\LATEST into your private branch” but I’m pretty sure that almost no one understands what this involves. In fact several people have spoken to me with problems relating to just that. Hence this article!

Let’s take a typical scenario. Create a private branch and check in a couple of new versions. Wait for your feature to get the go-ahead for main\LATEST check in. Merge main latest into your private branch. What will you end up with? Clearcase will check out every single file and directory in your view that has changed (in main) since you created your private view. Clearcase will then merge all those files into your branch; for the most part this will be a trivial merge because the version on your private branch won’t have changed. If your code has been on a branch for a while there may be thousands of files across the VOB that have nothing to do with you that will be merged. Each merge will create merge lines from one branch to the other.

There is a simpler and quicker way which involves a lot less hassle (and scary merge lines):

  1. When you have finished your new feature and checked everything in on to your [private] branch.
  2. Make a note of the private branch’s name.
  3. Go into Clearcase explorer, right click on the view and select “Finish private branch".
  4. Clearcase pops up a merge box so select “Leave my changes on Private branch".
  5. Clearcase will kick off an “Update". If you’re on a dynamic view this will be instant whereas if you’re using a snapshot view then get yourself a coffee.
  6. When the update has finished, go back into Clearcase Explorer and right click on the view name and click “Set up private branch".
  7. The dialogue will pop up asking for a branch name, so enter the branch name you wrote down earlier.
  8. Clearcase will pop up a warning about reusing the branches so click “OK” to say that’s fine.
  9. Clearcase will kick off another update, so if you’re on a snapshot view you can go to the toilet to get rid of that coffee and dynamic view users can move to the next step. The update process will copy the items on your branch into the local view.
  10. You are now on your private branch again only the private branch timestamp has moved forward. All the files that have not been modified by you (i.e. don’t have a version on your branch) will be updated to the latest version. Your view will also contain the files on your branch.
  11. Now if you merge main latest into your private branch only the files that have changed on main latest AND your branch will be merged together.
  12. Now you are free to continue working with the latest code base. If you decide to check in your code (i.e. merge your private branch into main) then all the merges will be trivial.

NRA Open Day Ticket Sales

April 23rd, 2012

Each year I organise a Beer and Guns day. We meet in the morning and drive to Bisley and take part in the NRA Open Day. After a day of shooting we leave, drive back to Reading and go to the CAMRA Real Ale and Cider Festival.

One particular year I delayed buying my tickets and they sold out. I am a member of the NRA [ NRA-UK not to be confused with the American NRA, which has done more damage to itself than any government could have done :) ] so I phoned the organiser and begged them to create an extra place for me. They said that’s a bit cheeky but as I was actively promoting the sport by getting friends to come, they would make an exception for me.

The Open Day registration page displays the number of tickets remaining so I thought I’d put some of my super skills together to produce a graph of how quickly the tickets are sold, so I and others won’t get caught out again.

5 May 2012 NRA Open Day 5 May 2012 Ticket Sales

It’ll be interesting to find out if the sales behaviour changes year-on-year… yay more graphs for another day.

Creating a mail list inside Lotus Notes

April 16th, 2012

Mail lists are called mail groups inside Lotus Notes.

  1. Go to Lotus Note desktop.
  2. Double click on MrN Address Book on MyServer (MrN = your name, MyServer = probably Local).
  3. From the tool bar, Action -> New -> Group.
  4. Fill in group name.
  5. Fill in Members.
  6. From the window tabs, click Save & Close.