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Written By : Amit
Title :
mapping class hierarchy table per subclass
Description :
Example
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Title :
ways create Hibernate SessionFactory
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ORM Hibernate Best FIT
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Written By : Amit
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Interview questions answer
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| Hibernate Tutorial,Interview-Questions,On-Hibernate
Author : Amit
Date (Year/Month/Date): 2009-01-28
Hibernate interview question 1:
When or How will the Persistent objects become Transient Objects?
Hibernate Interview answer :
Persistent objects are those, that are having database/ persistence value
with primary key value present in the domain object in memory.
Transient objects are those, that are never associated with persistence
and not having corresponding record / row in database table.
Now when persistent object turns to Transient object? this situation
may arise normally when the record is deleted from the database.
In this case there is no way the domain object in memory be mapped to any
particular persistence context.
* Note from Author:
If anybody has any difference of opinion, please write it by replying
to this question.
Hibernate interview question 2 :
Can you use final class as domain class for making the instances as
persistent object?
Hibernate interview answer :
Yes, one can use final classes for instantiating to become persistent
object.
Hibernate interview question 3 :
What is the difference between Java identity and Persistence entity
from Hibernate perspective?
Hibernate interview answer :
While a domain object is in memory, then the equals() and hasCode() methods
can be used for identifying domain object in memory, this way Java identity
of domain object can be established. While Persistence identity is related
to the primary key column and its value present in database table.
Hibernate interview question 4 :
Under what circumtances, is it required to implement equals and hasCode methods?
Hibernate interview answer :
There are two situations, where it is required that equals() and hasCode()
methods should be implemented are as follows:
1. When there is one to many or many to one or many to many mapping, and the
many part is contained in java.util.Set for holding all the mapped
objects. As implementing class for Set interface, like java.util.HashSet
uses equals and hasCode for operating certain methods like containsKey etc.
2. When any detached object is to be added back another Hibernate Session
for converting the detached object to persistent object.
Hibernate interview question 5 :
Can you have a final class implementing an interface and use it with
lazy="true" ?
Hibernate interview answer :
Yes, it is quite possible.
* Note from Author:
If anybody has any difference of opinion, please write it by replying
to this question.
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Commented By ->
Guddu | Hibernate Question :
Can the strategy of LAZY load for the dependent domain classes,
be change once SessionFactory is created?
Answer to the Best of my knowledge:
No, as SessionFactory is loaded/created once for the entire
lifecycle of the application,and while creating Hibernate
SessionFactory, appropriate HBM XML file is read and these
configuration are used for creating or instantiating Hibernate
SessionFactory, so it is logically not possible as,
SessionFactory is not going to refresh but destroyed and
recreated. And for different modules from the same
application, if requires LAZY as true / false, then using a single
Hibernate SessionFactory won't be able to serve both these
Persistent Object loading strategies. |
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Commented By ->
Girish | Hibernate Interview question :
Is it possible to change LAZY loading strategy of persistent dependent object?
Like changing Lazy value from true to false.
Answer to the best of my knowledge on Hibernate
No, while Hibernate SessionFactory is getting instantiated by using configuration
parameters those are specified in HBM XML file, so once Hibernate SessionFactory
is created, it will have to be destroyed and re-created to be able to take any
changes in configuration, such as lazy value changed from true to false or
vice versa.
|
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Commented By ->
Girish | Thanks for these Hibernate interview questions.
Can you provide some more questions, based on practical
questions from projects? |
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Commented By ->
Girish | Hibernate Interview question :
Is it possible to change LAZY loading strategy of persistent dependent object?
Like changing Lazy value from true to false.
Answer to the best of my knowledge on Hibernate
No, while Hibernate SessionFactory is getting instantiated by using configuration
parameters those are specified in HBM XML file, so once Hibernate SessionFactory
is created, it will have to be destroyed and re-created to be able to take any
changes in configuration, such as lazy value changed from true to false or
vice versa.
|
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Commented By ->
Amit | Hibernate Question
what are the differences between Projections and Restrictions in Hibernate?
Answer to Hibernate Question
In Hibernate, Projections can be used to manipulate groups functions, like
in SQL we have group functions like COUNT, MAX, MIN, AVG, SUM, DISTINCT etc.
While Restrictions can be used with conditional operations such as in SQL
we have like, greater than (>), less than (<), equals to, in, between, is null or
not null and many more.
|
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Commented By ->
Amit | Hibernate Question
What is the difference between Component mapping and association mapping
in Hibernate Mapping?
Answer
To the best of my understanding,
Component mapping between two class files, such as for example
company class file and department class file, can have a composition
relationship. So this means that class department should be mapped
within the company class definition. So this is the way component mapping
is done, such as shown below:
<class name="company" table="company">
....
....
<component name="department" class="Department">
....
....
<component>
<class>
One thing to note here that Department component mapping does not take
table name as attribute, thus department class is not mapped as an Entity
in component mapping. So attributes of company and department
class files should have corresponding column defined in the common table,
for example in this case it is company table.
As Department is not having any independent identity in database, so this
is not an Entity that can be deleted alone. If company Entity is deleted,
then corresponding Department will be deleted as well. Thus Object-oriented
composition relationship/notation among different objects can be achieved.
But in case of association mapping, both the objects will have different
class tags in Hibernate mapping file, and having different tables, and
in this case these objects are having different identity and are Entities.
This is one of the different I can remember as of now, if anyone having
any comments on this, please write it here.
|
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Commented By ->
sourav | Association Mapping is usually happen between parent-child related tables,where
both the tables are dependent on each other with one-to-one or one-to-many or
many-to-many relationship. |
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