Types of hibernate bean states

As of we know hibernate follows the ORM features, Java bean class maps with database table. While mapping java bean class with database table it traverse through different types of states. That are Transient, Persistent and Detached states. 

Different states of POJO class object:
1. Transient state:
  • Object is created by programmer with data. But is doesn't represent any table row.
  • This object does not contains any primary key value.
  • The object which is created for POJO class and which is not under control of hibernate application resides in transient state.
2. Persistent state:
  • The object that represents table row with primary key and managed under control of hibernate software is called as persistent state.
  • This object will be in synchronization with table row. 
  • Hibernate application developer's uses this kind of object in persistent logic development.
3. Detached state:
  • when session is closed persistent context will be destroyed and all the objects which are in persistent state will be thrown to detached state.
  • when table row of persistent state object is deleted then object becomes detached state.
How the hibernate program is able to perform synchronization between java object and table rows?
Ans: Every POJO class object that is representing table row will contain primary key value which is one of the number variables of the object. Based up on this primary key value synchronization works.

Hibernate software uses this primary key value as a criteria to update row data using select query and object data with row by using update query.

Note: Programmer configures one or more of the member variables of POJO class as primary key field in hibernate mapping file.

What is Primary Key? What are different types of Primary key's are there?

Primary Key: Every record of a table should be identified uniquely. To do this we can configure primary key.

Single field primary key: If only one member variable of POJO class is configured as primary key field then it is called singular field configuration. To configure this we can use <id> tag in mapping file.

Composite primary key: If more than one member variable of POJO class is configured as primary key field then it is called as composite primary key. To configure this we can use <composite-id> tag in mapping file.

How synchronization will work when there is no primary key declared in database table?

If database table primary key is not specified then we can prefer unique key field to configure as a primary key in hibernate mapping file.
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