When we talk about java, we also come across this term Hibernate. It is an object-related mapping or ORM framework that implements JPA ((Java Persistence API) like many other ORMs available in the market. In, Hibernate you create units, a unit and nothing else, a Java class that will create a table for you in the database.
Below, we have given hibernate interview questions to provide fundamental conceptual data at the beginning and later, with particular significance to the topic. The information you provide will brush your mind and contribute significantly to impressing the interviewer.
What does Hibernate do in
Java in simple language?
Hibernate is a tool which handles easy interaction of the application with the database. When said ‘database’, it involves multiple tables, and each table might be inter-related with one another. This inter-relation between the tables in terms of Java can be said as entity-relationship (the relationship between entities). Having said this, I mean that for every table in the database, we have a corresponding entity in our Java application as well.
Hibernate eases out the effort of Java developers, by asking them to just create an entity mapping XML for each of the entities available in the application
What is Hibernate Framework?
Hibernate is an Object-Relational Mapping (ORM) solution for JAVA. It is mainly an open-source structure which was developed by Gavin King in 2001. It is light and high performing and powerful framework for any java application.
It allows users to avoid writing complex manual JDBC logic. You can say it’s a wrapper over JDBC. It also facilitates lazy loading which in term improves application performance as to avoid unnecessary DB hits.
How Hibernate framework works?
Hibernate is an ORM framework. Which creates an abstraction on top of any SQL supporting database. This abstraction is represented as Object (in hibernate or ORM terms ENTITY).
You create entities to map to a Table or Multiple tables. You can run SQL or hql on in hibernate.
Query query = session.createSQLQuery(“your SQL query”);
Query query = session.createQuery(“your HQL query”);
It maintains a Persistence context and Persistence unit where objects are maintained. It is kind of a container.
What the main components are of hibernate?
The primary components of hibernating are:-
- Session: it is used to connect a physical network to a database.
- Transaction: constitutes the working unit of the database.
- Query: SQL and HQL string are used to collect information from the database and to generate items.
- Criteria: Create and implement object-oriented queries and recover items.
- Configuration: reflects the correct configuration
What are the main features of Hibernate Framework?
The main features are: –
- Save items to a database
- Loading data into an object
- Navigating through objects without writing queries
- Data Caching (optional)
What is hibernate mapping?
In the hibernate mapping file hibernate application developer specify the mapping from entity class name to database table name and entity property names to the database table column names i.e., mapping object-oriented data to relational data is done in this files. standard name for this file is <domain-object-name.hbm.xml> In General, for each domain object we create one mapping file Number of Entity classes = that number of mapping XML files Mapping can be done through annotations also. If we are using annotations then no need for mapping XML files
How does hibernate search works internally?
First hibernate create configuration with annotations or mapping file internally.
Second it creates the instance of SessionFactory which is just like a engine for running other activities.
Third we create the session by using session factory instance and session is responsible for all work like insert, update, delete etc.
Where should the hibernate framework be used?
Hibernate is mainly used to access an RDBMS from your Java code. It maps your objects to database objects, and in a way reduces the effort required at the DAO layer. Databases become table objects, fields become class attributes, and CRUD operations become functions
What are the benefits of using Hibernate ORM?
Hibernate is a persistent layer that is used to develop a persistent component. Here are some benefits of Hibernate ORM
- It is a database-independent that can work on any database you want. It provides HQL (Hibernate Query Language) which is compatible with any database server.
- Hibernate to provide coaching mechanisms means that you do not need to hit the database for similar queries, you can use it from buffered memory to improve and improve performance.
- It efficiently supports Lazy loading which is also called n + 1 problem in Hibernate.
What is the use of annotations in hibernates?
Annotation is a new technique for ORM without using the .hbm.xml file. But compared to XML bcz XML file the annotation can change the configuration without creating less object and Hibernate prefers the first XML file but reduces the time for annotation mapping and table and field mapping.
Is a Hibernate session object thread-safe?
No, the Hibernate session object thread is not protected. Each thread must find its session instance to close things.
What is the difference between getting () and Load () methods in Hibernate?
Session. This is executed by lazy loading by default when working in the load () method, which means that the Hibernate Framework retrieves the records for the domain class object from the DB table, as long as it returns the proxy object to the application As shown below
EmployeeDetails emp = session.load (EmployeeDates.class, 6011);
The load () method generates 1 for the proxy object and one for the real object.
The dummy object that represents the presence of a real object until the real object arrives is called a proxy object.
The load () method is suitable for checking whether a record is available or not.
The get () method should be available using the record we assume, otherwise, it throws ObjectNotFoundException
The get () method performs eager loading that cannot generate any proxy objects. This is a direct hit to the database. Whether or not this check record is available, this application may terminate normally.
What is the main and most important between save and saveOupdate method in Hibernate?
The difference is b / w Save and SaveOrUpdate:
When you stop the save method it erases existing data and replaces the current data you are inserting.
And saveOrUpdate ():
This is the method when you first hit the method it goes into the database then check the data. If there is a data change then only those fields that have the same remaining things are the same.
What is the difference between saving and maintaining Hibernate?
Here is the difference between save () and persist () of Hibernate:
(1) The primary difference between save () and persist (save) (save) is used outside the transaction limits, where the transistor () must be used within the transaction limits.
If I am calling save () multiple times in the same session, then the duplicate rows in the database may end.
If we are calling Persist () multiple times in different sessions that may end up with a unique row in the database. Note that the use of persisting () should only be in the scope of the transaction.
(2) save () returns nothing. Remain anywhere () returns the specific identifier associated with the transaction provided. Although both methods change the state of the hibernate unit from transient to permanent state.
Suppose call, save () call multiple times with the same transaction scope will not be able to understand the save () of hibernate, is it for the same identifier or different ones. Every time a call to save () is the result of a new row in the database. (). No one can control the duplicity of records.
When calling Persist () returns the unique identifier associated with the particular entity object. For this, the inserted query will be removed. The duplicity of records can be controlled.
(3) Save () return type is zero where Persist () is long type value
What is the Hibernate Cache mechanism?
Hibernate is much more than an ORM tool as it can be used to implement caching.
Cache is used to minimize the number of db round trips & resource consumption
Hibernate supports different types of cache:
First Level Cache: Hibernate first level cache is associated with a session object or known as a session cache. It is enabled by default and is a mandatory cache through which all requests must pass. Any object placed in a session will not be visible in other sessions and when the session is closed, all the cached objects of the session will also be lost.
Second Level Cache: Hibernate second level cache is an optional cache and we can enable it through configuration. Hibernate has not yet implemented the second level cache. But we can use Cache providers such as EHCache or Infinispan, etc. which implement this cache.
The query cache is provided with a combination of queries and values as keys, and caching the list of identifiers of objects returned by the execution of the query as values. Note that Hibernate will load objects using cached identifiers from another level.
Why hibernate over JDBC?
Because the JDBC have a lot of problems like all exceptions are checked exceptions so we need to take care of all those things i.e using try and catch block or by throwing the exception as well as we need to take care of creating the Connection and closing the connection so like there are a lot of benefits are there.
What are the options to disable second level cache in Hibernate?
This is a trick question. By default, Second level cache is already disabled in Hibernate.
In case, your project is using a second-level cache you can use one of the following options to disable second level cache in Hibernate:
You can set hibernate.cache.use_second_level_cache to false.
You can use CacheMode.IGNORE to stop interaction between the session and second-level cache. The session will interact with cache only to invalidate cache items when updates occur.
What are some of the databases supported by Hibernate?
Hibernate supports almost all of the databases whether it is SQL DB such as Oracle SQL or NoSQL DB such as MySQL, Cassandra, Maria DB, Mongo DB, etc
All you need to do is mapping with your existing application and rest will be taken care of by Hibernate framework itself.
Can we add multiple databases in one configuration file in Hibernate?
Yes. But it cannot be done using one hibernate configuration file. You need to have two configurations files for it.
What is Dialect in the configuration file in hibernate?
It simply tells the database to hibernate is going to connect you to. Hibernate needs to be aware of this in advance in order to produce an appropriate type of SQL statements on database type.
What is lazy initialization in hibernate?
Lazy loading” means that an entity will be loaded only when you actually access the entity for the first time. This method is used to load the dependent components of some Java beans just when needed. It helps in saving a lot of memory and computational resources and improves the overall performance. Which components to lazy load is a designers choice and it boils down to different factors, like what is the frequency of usage of the part, how long it takes to actually load to the memory, etc.
What are main hibernate Interfaces?
The following is a list of Hibernate’s main interfaces:
Session Interface: Basic interface for all Hibernate applications. Examples are lightweight and can be built and destroyed without costly procedures.
SessionFactory Interface: The distribution of session objects is done by this interface to hibernate applications. For the entire application, there will usually be one session factory and can be shared by all application threads.
Configuration interface: The Hibernate bootstrap operation is configured by this interface. The location specification is specified by specific mapping documents, followed by an example of this interface.
Transaction Interface: This is an optional interface. This interface is used to intercept transactions from code that is implemented as JDBC / JTA transactions.
Query and Criteria Interface: In addition to controlling the flow of query execution, queries from the user are allowed by this interface.
How to create a SQL query in Hibernate?
Hibernate provides a SQL inspired language called Hibernate Query Language (HQL) to write SQL-like queries against Hi Byrne’s data objects. HQL is an object-oriented version of SQL. You can see this in Hibernate’s documentation (Chapter 15. HQL: The Hibernate Query Language). To start at a more basic level and one that is more example oriented, use the tutorial from Tutorial Tutorial (Hibernate Query Language).
Will using hibernate slow down the application performance?
Yes slightly, because hibernate is an ORM framework has its own APIs and programmer uses the hibernate’s APIs which further uses the JDBC, but it provides DBMS independent platform.
What is the dialect in Hibernate’s configuration file?
It simply states that you will be connected to the Hibernate database. Hibernate must be conscious of it in advance to generate the suitable SQL declaration on the database type. What is hibernate lazy initialization?
Can we add multiple databases to a configuration file in Hibernate?
Yes. But this cannot be done using a hibernate configuration file. For this you must have two configuration files.
Why is Hibernate so complex?
It is quite simple to use for particular use cases and quite complex for others. Like any piece of technology, it is simple for use cases it was designed to address initially. It becomes complex as it is used to cover other use cases not part of its original design considerations. You can’t please everyone.
What are pitfalls or difficulties in using Hibernate as ORM?
With the increased complexity in the business logic, Hibernate is becoming difficult to handle. The main issue with Hibernate (or any other ORM) is that it violates the encapsulation principle of OOP. Other pitfall are with Transactions and complex queries are definitely challenging. But the most common mistake that is commonly seen people doing is using ORM for the batch processing. Apart from that Hibernate multitenant support which got added recently is little tricky.