Hibernate

Introduction:-

Hibernate is a free tool used in Java programming that allows data to be  inserted, removed or changed in a  database without paying a lot of attention to how it gets there. So SQL is used—Hibernate does that.

Hibernate was founded by Mr. Gavin King, an Australian developer who needed to solve a problem and ended up creating Hibernate, an open source tool that is amazingly useful. 

When Can I Use Hibernate: 

• Hibernate can be used in any Java program that needs to access a relational database. 
• Hibernate does not need an application server to run in. 
• Hibernate can be used in any Java class with really no other dependencies other than on a single Hibernate JAR file and one configuration file.

When Should I Use Hibernate:

According to The Man himself [Gavin King], you should only consider using Hibernate if:

• You have a non-trivial application. 
• You have more than 10 tables in your relational DB. 
• Your application uses an object-oriented Domain Model.
• If your application does a lot of business logic—and does much more than just display tables of data on a webpage—then it is a good candidate for Hibernate.
• Hibernate is best in applications with complex data models, with hundreds of tables and complex inter-relationships. 
• In a normal JDBC application, you deal with populating a List of POJOs with data you manually pulled from a ResultSet.

How Hibernate Works:

• Hibernate does not force you to change your POJOs.
• Hibernate does not force you to implement any interface.
• Hibernate works on any POJO.
• Hibernate requires 1 overall configuration file.
• That 1 configuration file tells Hibernate
• à Which classes you want to store in the database.
• Each mapped class needs an additional configuration file.
• à How each class relates to the tables and columns
•      in the database.

BigData/Hadoop

Pagination with BC4J

There are two ways to to do pagination in BC4J.

There is one in build pagination is available in BC4J.

Create you VO object.
then
vo.setAccessmode(RowSet.PAGING_MODE);
vo.setWhereClauseParam(0,25);//for ROWNUM <= section
vo.setWhereClauseParam(1,0);//for ROWNUM> SECTION


Other-way to do this is.

Have one method like below

setPagingQuery(ViewObjectImpl vo){
vo.setQuery("SELECT * FROM (SELECT /*+ FIRST_ROWS */ IQ.*, ROWNUM AS Z_R_N FROM(" + 
                             vo.getQuery() + ")IQ  WHERE ROWNUM < " + end + 
                             ") WHERE Z_R_N >" + start);
}

then before your do execute your query. just call
setPagingQuery(this);
excecuteQuery();

How to get the five highest-paid people—a top- N query

SELECT *   FROM (SELECT *             FROM emp         ORDER BY sal DESC)  WHERE ROWNUM <= 5;