Hibernate Interview questions Part2

16.What’s
the difference between load() and get()?

load() vs. get() :-

load()	get()
Only use the load() method if you are sure that the object exists.	If you are not sure that the object exists, then use one of the get() methods.
load() method will throw an exception if the unique id is not found in the database.	get() method will return null if the unique id is not found in the database.
load() just returns a proxy by default and database won’t be hit until the proxy is first invoked.	get() will hit the database immediately.

17.What is the difference
between and merge and update ?

Use
update() if you are sure that the session does not contain an already
persistent instance with the same identifier, and

merge()
if you want to merge your modifications at any time without consideration of the
state of the session.

19.Define cascade and inverse
option in one-many mapping?



cascade - enable operations to cascade to child entities.

cascade="allnonesave-updatedeleteall-delete-orphan"



inverse - mark this collection as the "inverse" end of a bidirectional
association.

inverse="truefalse"

Essentially "inverse" indicates which end of a relationship should be ignored,
so when persisting a parent who has a collection of children, should you ask the
parent for its list of children, or ask the children who the parents are?



20.What does it mean to be inverse?



It informs hibernate to ignore that end of the relationship. If the one–to–many
was marked as inverse, hibernate would create a child–>parent relationship (child.getParent).
If the one–to–many was marked as non–inverse then a child–>parent relationship
would be created.



23.Explain Criteria API

Criteria is a simplified API for retrieving entities by
composing Criterion objects. This is a very convenient approach for
functionality like "search" screens where there is a variable number of
conditions to be placed upon the result set.

Example :

List employees = session.createCriteria(Employee.class)

          .add(Restrictions.like("name", "a%") )

          .add(Restrictions.like("address", "Boston"))

   .addOrder(Order.asc("name") )

   .list();

24.Define HibernateTemplate?



org.springframework.orm.hibernate.HibernateTemplate
is a helper class which provides different methods for querying/retrieving data
from the database. It also converts checked HibernateExceptions into unchecked
DataAccessExceptions.

25.What are the benefits does
HibernateTemplate provide?

The benefits of HibernateTemplate are :

• 
  
HibernateTemplate, a Spring
  Template class simplifies interactions with Hibernate Session.


• 
  Common functions are simplified to single
  method calls.


• 
  Sessions are automatically closed.
  


• 
  Exceptions are automatically caught and
  converted to runtime exceptions.

26.How do you switch between
relational databases without code changes?



Using Hibernate SQL Dialects , we can switch databases. Hibernate will generate
appropriate hql queries based on the dialect defined.



27.If you want to see the Hibernate generated SQL statements on console, what
should we do?



In Hibernate configuration file set as follows:

true




28.What are derived properties?



The properties that are not mapped to a column, but calculated at runtime by
evaluation of an expression are called derived properties. The expression can be
defined using the formula attribute of the element.



29.What is component mapping in
Hibernate?

• 
  A component is an object saved as a value,
  not as a reference


• 
  A component can be saved directly without
  needing to declare interfaces or identifier properties


• 
  Required to define an empty constructor
  


• 
  Shared references not supported

Example:

30.What is the difference
between sorted and ordered collection in hibernate? sorted collection
vs. order collection :-

sorted collection	order collection
A sorted collection is sorting a collection by utilizing the sorting features provided by the Java collections framework. The sorting occurs in the memory of JVM which running Hibernate, after the data being read from database using java comparator.	Order collection is sorting a collection by specifying the order-by clause for sorting this collection when retrieval.
If your collection is not large, it will be more efficient way to sort it.	If your collection is very large, it will be more efficient way to sort it .