Sudhanshu Mishra

hey all,

I tried finding it out myself and understood that NAN is printed because when first time giveLife is called, there is no 'life' property in Jay, but then
inside giveLife function, it actually gets created.Now since we added 1 to it without giving it any initial value, we got NaN. Now as a side- effect, Jay has a property life with value 'NaN'.prototyping it does not
override it.

Is this understanding correct?

Hi all,

I want to understand the behavior of 'prototype' in JS.
I have written below code:

function User() { this.name=""; this.life = 100; this.giveLife = function(targetUser){ targetUser.life +=1; } } function Users(){} var Barry = new User(); var Jay = new Users(); Barry.name="Barry"; Users.prototype.life = 60; Barry.giveLife(Jay); /*Users.prototype.life = 60;*/ console.log(Barry.life + " :::giveLife::: "+Jay.life); Users.prototype.takeLife = function takeLife(targetPlayer){ targetPlayer.life -=1; } Jay.takeLife(Barry); console.log(Barry.life + " :::takeLife::: "+Jay.life);

Output is :

100 :::giveLife::: 61
99 :::takeLife::: 61

However, if I comment out line 16 and uncomment line 20, what I get is below:

100 :::giveLife::: NaN
99 :::takeLife::: NaN

I get the "100 :::giveLife::: NaN" part, but I was expecting "99 :::takeLife::: 61" as I added 'life' for Users to be initialized, via prototype.

Please suggest what I am doing wrong.

Thanks in advance

Hi Ranchers

I am aware that Hibernate uses JDBC API for persistece.
However, I have one query regarding JDBC transactions in Hibernate. I am posting the below snippet and have written what I understand from each line of code:

Session sess = factory.openSession(); --> This starts a Hibernate session, but still does not fetch any Connection from Connection pool(assuming it is configured) Transaction tx = null; try { tx = sess.beginTransaction(); --> This fetches the Connection object from Connection pool, sets autocommit as true, and starts a database transaction. // do some work ... tx.commit();--> This commits all the changes to the database and marks the database transaction as complete. } catch (RuntimeException e) { if (tx != null) tx.rollback(); throw e; // or display error message } finally { sess.close(); --> This closes the session and returns the Connection object to the pool. }

Could you please verify and correct my understanding, before I study further?

Thanks

Thanks Fritz.

Hi Ranchers,

Today I cleared OCEJPA Exam - 1Z0-898 with 83% marks.
First of all a big thanks to all the ranchers who helped me with all my queries while preparation.

I would summarize my method of preparation for this exam, which could benefit others preparing for the exam.

1:Most important - Get the basics right. Be sure of what is guaranteed and what is dependent on the provider.("May be /might be/Must be" kind of stuff).
2:I chose Apress-Pro JPA2 for my preparation and prepared till chapter 13. It is a very good book and gets you familiar with the concepts easily.
3:When in doubt , CODE. Write lots of code snippets to understand the concepts with clarity.
4:Last but not the least, do give a read to JSR-317.It would give you a clear picture of what the Spec says, and the exam questions might have exactly same lines from the spec.
5:Enthuware - Great exam taking tool. This helped me a lot to identify with the exam pattern and my weak/strong areas.

I had a very little experience in JPA. I used to prepare 2-3 hours each day and it took me a month to be ready for the exams.

My Exam Experience:
The questions were a bit difficult and had really close answers.The time, however, was sufficient.
The questions came in a sequential order .i.e. a set of questions from Entity basic mappings, then a set of questions on locking, then a set on Criteria API and so on.
No question on automatic key generation.
Many questions on transactions, Criteria API , locking and caching.

Please let me know if any further information required.
I would be glad to help.

Thanks,
Sudhanshu

Please help.

Hi ,
Why does a persist method on a removed instance makes it managed , while a merge operation on a removed instance throws an exception.
I am confused as the spec says that a removed instance is still associated with the persistence context.
So why different behavior from persist and merge on a removed entity?
Basic confusion is how to decide when a particular operation will throw an exception.Can we decide it on the basis of an ID conflict , or on the basis of presence of a persistence context?

Thanks

Hi All,
I am a bit confused after reading JSR-317 Section 3.2.8(Managed Instances).

As far as I understand, if an entity is associated with a persistence context, it is managed.
And as per the spec: A managed entity instance is an instance with a persistent identity that is currently associated
with a persistence context.

Then why invoking contains on a removed entity will return false?

Please help me understand the concepts.

Many thanks in advance.

Hi All,
I was going through the JSR-317 and I stumbled across this statement:

Such schema-level mapping annotations must be specified on the owning side of the relationship. Any
overriding of mapping defaults must be consistent with the relationship modeling annotation that is
specified. For example, if a many-to-one relationship mapping is specified, it is not permitted to specify
a unique key constraint on the foreign key for the relationship.

But Many-to-One side IS the owner, then why can it not modify the uniqueness of Foreign Key?

I am new to JPA .Please help me with the basic concepts.

Thanks

HI All,
I am a bit confused regarding the concept of Directionality in JPA.
Why is it important to consider the directionality?
I understand that an entity having a reference to other entity accounts for a direction, but is it all to it?
Do my mapping annotations have any thing to do with directionality, or they simply indicate the cardinality?

Help me get the basics straight.

Thanks in advance.

Thanks for the reply,Rafael de Sousa
If you read the question completly, I also referred that it was mentioned in the Pro JPA 2 book.
Thanks for helping me get this straight though.

Hi all,
Is my question missing any details?
If not, why no answers yet?

Any replies?
I think I have provided the complete details, still if further information required please reply.

HI,
I am learning JPA from book Pro JPA 2- and I have a doubt in the topic - ID Generation using the Table
My doubt is regarding @TableGenerator
When I used

@Id @TableGenerator(name="XYZ") @Id@GeneratedValue(generator="XYZ" )
it behaved like AUTO strategy.(Did it happen because I missed the strategy? But no such mention in the book :S)

When I gave the table name as below:
@TableGenerator(name = "Emp_gen",table = "ID_GEN" , pkColumnName="id_gen" ,pkColumnValue="Employee_GEN", valueColumnName="key_value", initialValue=150) @GeneratedValue(generator="Emp_gen")
it still behaved like AUTO, even though I have the table this time in my database as

+-----------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+-------+
| id_gen | varchar(100) | NO | PRI | | |
| key_value | int(11) | YES | | NULL | |
+-----------+--------------+------+-----+---------+-------+

Please clarify as the behavior is not clear to me.
I came across this while trying to code the examples in the book and when they did not work as expected (Used Hibernate and MySQL) .

Please help me with the problem and let me know if further details required.

Thanks

HI
Does server uses JNDI under the hood to perform a dependency injection of EJBs ?
Please reply.

Thanks,
Sudhanshu