About Hibernate Save and Delete parent children again

I want to add new child object into children collections and remove 'selected' existing child object from the same children collections.

1. First, i get the collection from 'attached' parent. For e.g Set children = parent.getChildren()
2. Add the new Child object. Of course please save the Child object first. children.add(newChild).
3. Remove the 'selected' existing Child object. children.remove(removedChild)
4. Finally, save the Parent object.

It is kind of fundamental. However sometimes we may get confused due to whatever reasons.

OpenOffice mail merge problems

I need to merge document B to document A(master document) using OpenOffice SDK.

My font in document B is 'Arial' and there are 3 paragrahs in it.

After merging, the font of the last paragrah somehow changed to 'Times New Roman'!

Another problem is, document A is formatted with numbering, document B is supposed to be inserted at the first line of the numbering. However, the 2nd paragraph from document B ends up a new number within the numbering format! To be more specific, document B's content should be positioned at number 5.1, but right now document B's content has been splited into 2: 5.1 which is the 1st paragraph from document B and 5.2 which is the 2nd paragraph from document B. My intention is to put all paragraphs from document B into 5.1!

After few days of searching, i discovered that it is actually a bug in OpenOffice!

1. http://qa.openoffice.org/issues/show_bug.cgi?id=60475



2. http://www.oooforum.org/forum/viewtopic.phtml?t=60268&highlight=insertdocumentfromurl+format

My solution:

1. To solve the numbering problem, document B must always have an extra paragraph break after the last paragraph! (If you are using OpenOffice, click View from menu and choose to show "Nonprinting Characters")
   
   


2. To solve the style problem, i adjust the styles in document A again after the merging is done.
   
   

Differences between response.sendRedirect & response.forward methods

Came across one good explanation below, share with you guys out there:

Forwarding the Request and Re-Directing URL are two totally different animal. Your server gets the request from the browser..job of server is to send back the response. How how that response is generated is totally up to your server..you can process that request in one servlet or can process the same request using multiple sevlet...To process request using multiple servlet, you need to pass the request to another servlet...and ofcouse we do not want to loose the parameters/data set into the request otherwise that request does not make sense anymore.....This is all request forwarding!...Request forwarding is done during one HTTP request-response cycle..Once you return the response, you are done!

Now, In the response, you can tell your browser to do URL redirect to any other URL..this is HTTP header thing and browser will interprete the HTTP header and will send brand new request...

Delete procedure of One to One relationship in Hibernate

I found out that Cascading does not work for 1-to1 relationship. We have to cater for it specifically.

The story is, i mapped 2 entities with each of them having a "many-to-one" relationship to represent a 1-to-1 relationship. I did not use the "1-to-1" mapping because it caused some problems which i now can not remember anymore.

Let's call the 2 entities as "parent" and "friend". 1 parent has 1 friend.

Now, I want to just delete "parent" and hope that its children will get deleted automatically.

1. Therefore i will do a "session.delete(parent)". However this will throw an exception saying that "parent" is referencing another entity "friend".


2. So, I will now get the "friend" from "parent" first by doing "Friend friend = parent.getFriend()".


3. Then, i do a "parent.setFriend(null)" and saved the parent by doing "session.save(parent)". The "parent-friend" 1-to-1 relationship is being removed now.


4. Next i delete the friend by doing "session.delete(friend)".


5. Lastly, i will do a "session.delete(parent)". The parent will now be removed together with its children!

Hibernate Dialect

Today one problem arose. User complaint that one of the screen's query process takes too long time! I spent hours trying to figure out why. In the end found out that the Hibernate Dialect should be changed to MySQL instead of MSSQl one!

That is funny because my system is running on a MSSQL database! How can i just put MySQL dialect for Hibernate!

Well, it really speeds up the searching process.

Hell....

Funny Unix Symbolic Link to Windows Server issue

I faced this while doing deployment of one system to a unix server.

There is a folder/directory which is the symbolic link to a folder hosts at a windows NT server.

It is meant for clustering. The idea is 2 servers put the files/documents at the same folder at one location.

So, everytime i build my source code and deploy the war file at the unix server, i will run a program which runs the data migration. During the process the program will make use of the "open office service" that resides behind the operating system to create document such as Word and put at that particular folder as mentioned above.

Nightmare came. System kept throwing errors. The error message said it has something to do with "wrong code blar..".

I thought it was due to my code. Then I spent days to investigate the problem and to examine my code. It was a wrong move, a waste of time because in the end i found out that it is actually the program failed to create new directory! Ok reason found. The funny thing is, i tried to create the directory using unix shell command manually but failed! I did a list files command and found out that there is no such folder! But why did Unix say the folder is there? Ain't it funny!

Later i discovered that the folder is actually hidden. However i still did not manage to remove the folder by using the "rm -f ." command. From the net i know that this command works all the time to remove hidden directory. Clearly it did not work out in my case. So how now?

Finally i recreated the directory that the Unix claimed exist at the Windows Server, which is the "parent" cluster machine that holds the folder. After that i removed the folder again from the Shell at the Unix server. Yahoo! This time everything is back to normal! My program ran successfully!

What a waste of time. Was in the wrong direction. The Open Office Service should throw a more "exact" or "meaningul" message.

Nevertheless, I still do not know WHY and HOW did this problem happen! I only know the solution so far!

Somthing about Set in Java

Well, if you read about the Java API, you will know that Set will only add object that does not exist in the Set itself. You must be aware of this especially when working with Hibernate! Here's my experience:

I was trying to add a few objects in a Set and set this Set. Then I found out from the database that there is always only ONE object added. I did a debug and found the size of the Set is always > 1 !!!

What happened? Here is my answer from torough checking:

Only the 1st object had been added to the Set. It is because the rest are actually "equal" to the first object so Set does not take them anymore! Bear in mind that each object differs from each other using their ID field. They do have their own ID yet when they are being added into the Set so they are rejected by the Set!

Thus, i have to save each object first before adding them into the Set. The reason is the ID will be generated by Hibernate for each object. The Set knows that they are NOT EQUAL right now then they will be added.