Hibernate Interview Questions Part 2

1.What is 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.

2.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.

3.How do you define sequence generated primary key in hibernate?

Using <generator> tag.
Example:-

<id column="USER_ID" name="id" type="java.lang.Long"> 
   <generator class="sequence"> 
     <param name="table">SEQUENCE_NAME</param>
   <generator>
</id>

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

cascade - enable operations to cascade to child entities.
cascade="all|none|save-update|delete|all-delete-orphan"

inverse - mark this collection as the "inverse" end of a bidirectional association.
inverse="true|false"
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?

5.What do you mean by Named � SQL query?

Named SQL queries are defined in the mapping xml document and called wherever required.
Example:

<sql-query name = "empdetails">
   <return alias="emp" class="com.test.Employee"/>
      SELECT emp.EMP_ID AS {emp.empid},
                 emp.EMP_ADDRESS AS {emp.address},
                 emp.EMP_NAME AS {emp.name} 
      FROM Employee EMP WHERE emp.NAME LIKE :name
</sql-query>

Invoke Named Query :

List people = session.getNamedQuery("empdetails")
       .setString("TomBrady", name)
       .setMaxResults(50)
       .list();

6.How do you invoke Stored Procedures?

<sql-query name="selectAllEmployees_SP" callable="true">
 <return alias="emp" class="employee">
   <return-property name="empid" column="EMP_ID"/>       

   <return-property name="name" column="EMP_NAME"/>       
   <return-property name="address" column="EMP_ADDRESS"/>
    { ? = call selectAllEmployees() }
 </return>
</sql-query>

7.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();

8.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.

9.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.

10.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.

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

In Hibernate configuration file set as follows:
<property name="show_sql">true</property>

12.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.

13.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:

14.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. source:http://www.developersbook.com/	If your collection is very large, it will be more efficient way to sort it .