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|What is Hibernate?|
Hibernate is an Object/Relational Mapping solution for Java environments.
Hibernate not only takes care of the mapping from Java classes to database tables, but also provides data query and retrieval facilities.
|What is Object Relational Mapping (ORM)?|
Object/Relational Mapping refers to the technique of mapping data from an object model representation (Java Object) to a relational data model (database tables) representation.
|Explain advantage and disadvantage of ORM model?|
Advantages of ORM frameworks:
Database vendor independence: An ORM is abstracts layer for an application and gives you the portability to support multiple databases.
Reduction in development effort: An ORM frameworks manage metadata and API for database access and management,that increases productivity and speed up in coding.
Maintainability: An ORM work through configuration which allow sharing, reusability and fewer lines codes for DB operation that requires less maintenance.
Disadvantages of ORM frameworks:
Overhead: For simple and small applications, ORM framework can be overhead which required configuration, mapping and object management.
Performance impact: An ORM API do extra work to support efficient object state management with database table.
|What are the advantage of Hibernate?Or Difference between JDBC and Hibernate?|
Hibernate is database independent, same code will work for all kind of database like Oracle,MySql,SQLServerDerby, DB2PostGreSQL etc.
There is no need to create connection pools in case of Hibernate. Where in JDBC, connection pools need to be created.
Hibernate Supports Caching(1st level & 2nd level cache), that improve application’s performance andretains the objects in cache that reduce repeated hits to the database.While in JDBC you need to implement your java cache.
Development become fast,you don’t need to be an expert of writing complex and tune queries, as Hibernate take care of Query writing and tuning process .While in case of JDBC, its job of developer to write queries and tune them.
Hibernate support Lazy loading and Load objects only when required.
|Explain hibernate architecture? Or Basic Hibernate APIs?|
Hibernate architecture has following components:
Configuration (org.hibernate.cfg.Configuration):It represents database connection and O/R mapping setup. It will be used to build SessionFactory.
SessionFactory (org.hibernate.SessionFactory):It’s a Singleton, thread-safe and immutable cache of compiled mappings for a single database. SessionFactory instantiate Session object.
Session (org.hibernate.Session): A single-threaded, lightweight, short-lived object and designed to be instantiated on an interaction with database for persistent store.
Persistent objects and collections: Short-lived, single threaded objects containing persistent state and business function.These can be ordinary JavaBeans/POJOs and associated with org.hibernate.Session.
Transient objects and collections: Instances of persistent classes that are not currently associated with an org.hibernate.Session.
Transaction (org.hibernate.Transaction): A single-threaded, short-lived object used by the application to specify units of work and to maintain integrity in the database.
Query (org.hibernate.Query):It is an object oriented representation of Hibernate query that help w to retrieve data from database. A query instance is obtained by calling session.createQuery().
|What is hibernate SessionFactory and Session?|
SessionFactory: The SessionFactory is a heavyweight object, and there would normally be a single instance of this per application. It is thread-safe as it is created one per database and can be concurrently accessed by multiple threads. It is created using Configuration object and used to create session object.
Session: The Session is used to communicate between application and persistent store (database). This is factory for org.hibernate.Transaction. As it is not thread-safe, application should create and destroy it once a unit of work done though it may be used to multiple units as per requirement. It also represents a transaction in a database.
|Is hibernate SessionFactory thread safe?|
|Is hibernate Session thread safe?|
|What is POJOs?|
POJO (Plain Old Java Objects) is a simple Java Bean class with some properties. This class uses standard Java Bean naming conventions with private visibility of properties and getter and setter methods of that.
|What is caching and define it for ORM perspective?|
Caching is one of the important features implemented by an application for better Performance. an ORM perspective, data retrieved from a database is cached in memory or to disk, so there is no need to hit database for every request.
Cached data is available at three different scopes in an application:
Transaction scope: data is fetched in one session, and the same query is executed again in that same session before that unit of work is completed. This data is stored in memory/disk by default, so the call to the database for the second query is avoided. Because a unit of work is for one request, this data isn't shared or accessed concurrently.
Process scope: Data is cached across sessions or across units of work. If a query is executed in one session, and the same query is executed in a second session after closing the first, this data is cached so that the second call to the database is avoided. Because two requests can access the same data in these two sessions, this data is accessed concurrently. You should use this scope with caution.
Cluster scope: Data is shared between multiple processes on the same machine or on different machines in a cluster.
|Explain different caching strategies are in Hibernate?|
Hibernate have following three different caching strategies:
First-level cache: It is at the transaction level and enabled by default in Hibernate. Caching at the first level is associated with a session. If the same query is executed multiple times in the same session, the data associated with the query is cached.
Second-level cache: It is configured at the process level or the cluster level. In Hibernate, you can configure it for a particular class or for a collection to improve performance. You can use the second-level cache with large and complex object graphs that may be loaded often. It is associated with one SessionFactory and can be reused in more than one Session created from the same SessionFactory.
Query result sets cache: It is useful when you run a particular query often with the same parameters. By default, the queries aren't cached and requires two additional physical cache regions that hold the cached query result sets and the timestamp when a table was last updated.
|What is difference between transient,persistent and detached object in hibernate? Or Explain life cycle of an object in Hibernate?|
Object in hibernate has following states:
Transient - Objects instantiated using the new operator are called transient objects.
An object is transient if it has just been instantiated using the new operator, and it is not associated with a Hibernate Session. It has no persistent representation in the database and no identifier value has been assigned. Transient instances will be destroyed by the garbage collector if the application does not hold a reference anymore.
Persistent - An object that has a database identity associated with it is called a persistent object.
A persistent instance has a representation in the database and an identifier value. It might just have been saved or loaded; however, it is by definition in the scope of a Session. Hibernate will detect any changes made to an object in persistent state and synchronize the state with the database when the unit of work completes.
Detached - A detached instance is an object that has been persistent, but its Session has been closed.
A detached instance can be reattached to a new Session at a later point in time, making it persistent again. This feature enables a programming model for long running units of work that require user think-time. We call them application transactions, i.e., a unit of work from the point of view of the user.
|General Knowledge of India|
In 1897, the Birsa Movement supporters raised which colour flag as a symbol of Birsa Raj?
|Ratio and Proportion|
The cost of 10 books is Rs. 80/-. Find the value of 15 books?
The cost of 48 bags of paddy is Rs. 16,800/-. What is the cost of 36 bags of paddy?
Monthly expenditure of a family of 4 members is Rs 2800/-. What is the expenditure if there are 3 members in the family?
Annual incomes of the families of Sita and Latha are in the ratio 4:3 and their annual expenditure are in the ratio 3:2. What is their annual income if they save Rs. 3000/- in a year?
A certain sum of money is divided between A and B in the ratio of 5/4 : 5/3 and A got Rs. 360/-. Find the total sum of money and B’s share?
In an office, the ratio of the salaries of an officer and a clerk is 15:7. If the salary of a clerk is Rs. 720/- less than the salary of the officer, find the salary of each?
In an election to a municipal council, the votes secured by two candidates are in the ratio 13:19. The elected candidates gets 312 votes more than the second candidate. How many votes are secured by the second candidate?
A certain sum of money is divided between Murthy and Prasad in the ratio 22/7 : 8/3. If Murthy gets Rs. 120/- more than Prasad, find the share of each?
In a cricket test series, the runs made by Raju and Tendulkar are in the ratio 5:9 and Tendulkar and Azar are in the ratio 6:7. What are the runs made by them if Azar makes 187 runs more than Raju?
If A:B = 2:3 and B:C = 9:5 find A:B:C?
If A:B = 3/5:5/7 and B:C = 3/4:2/5, find A:B:C?
If R:S = 0.01:0.11 and S:T = 2.2:1, Find R:S:T?
In a school, Under a Saving Scheme, Rekha saves 3/2 times the savings of Bindu, Geeta saves 4 times the savings of Rekha. Find the ratio of the savings of all the three in least terms?
A man left 1/3 rd of his property to his wife and 3/5 th of the remainder to his daughter. He gave the rest to his son who received Rs. 6400/-. How much was his original property worth?
|Ratio and Proportion|
In a school 4/9 of the pupils are boys. There are 125 girls. How many boys are there?
If A:B = 3:4 and B:C = 5:6, find A:C?
IF X:Y = 3:4 AND Y:Z = 4:5, FIND X:Y:Z?
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