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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.
What is the value of cot 4π/3 ?
Article-24 of the Indian Constitution ‘Prohibition of employment of children in factories, etc’ deals with?
Article-134A of the Indian Constitution ‘Certificate for appeal to the Supreme Court’ deals with?
Who invented Aspirin?
A larger force on a rotating body results in larger?
What is the unit of the physical quantity, magnetic flux density?
The system of equations 2x + 4y = 6 and 4x + 8y = 8 is ?
|Time and Distance|
A thief is spotted by a policeman from a distacne of 100 m. When the policeman starts the chase, the thief also starts running. If the speed of the theif is 8 km / hour and that of the policeman is 10 km/hour, then how far will the theif have to run before he is overtaken?
Aman and Alok attempted to solve a quadratic equation. Aman made a mistake in writing down the constant term and ended up in roots (4, 3). Alok made a mistake in writing down the coefficient of x to get roots (3, 2). The correct roots of the equation are?
The effective annual rate of interest corresponding to a nominal rate of 22% per annum payable half-yearly is?
|Volume and Surface Area|
If the volume of a cylinder is 2156 cubic cm and height is 14 cm, find its radius?
What is the equation of the line which passes through the points (2, 3) and (- 4, 1)?
In △ABC, the angle bisector of ∠A cuts BC at E. Find length of AC, if lengths of AB, BE and EC are 9 cm, 3.6 cm and 2.4 cm?
In a triangle, the length of the opposite side of the angle which measures 45° is 8√2 cm, what is the length of the side opposite to the angle which measures 90°?
|General Knowledge of India|
The boundary line between India and Pakistan is called?
Which city is located on the banks of the river Mahanadi?
When was the battle of Haldighati fought?
In 1498, which Portuguese explorer discovered a new sea route from Europe to India?
|General Knowledge of India|
Chapchar Kut is a festival of which State?
In chemistry, soap is a salt of a ?
Which of the following is a Direct tax?
Sauria lacertidae is the scientific name of?
Which of the following is a primary function of haemoglobin?
A factory buys 8 machines.3 Machine A, 2 Machine B and rest Machine C. Prices of the machines are 100000, 80000 and 45000 respectively.Calculate the average cost of these machines?
Ticket for an adult is 500 and a child is 200. 1 child goes free with two adults. If a group has 20 adults and 8 children what will be the discount the group get?