On Hibernate Interview Questions Hibernate Tutorial Example

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Hibernate Tutorials: Hibernate Case Study Class Hierarchy Persist Example Using Hibernate Interceptor Hibernate Questions with Answer Hibernate Many-to-Many Mapping Example Hibernate one-to-many Mapping Example Hibernate and ORM tools Spring Hibernate Example Hibernate SessionFactory Example Hibernate Mapping Class Hierarchy Hibernate Questions Hibernate SessionFactory Questions Spring Hibernate Example: Spring Hibernate Case Study

Tags/Keywords : On-Hibernate - Interview-Questions - Hibernate-Tutorial Example
Author : Amit
Date (Year/Month/Date): 2009-01-28 Hibernate interview question 1: When or How will the Persistent objects become Transient Objects? Hibernate Interview answer : Persistent objects are those, that are having database/ persistence value with primary key value present in the domain object in memory. Transient objects are those, that are never associated with persistence and not having corresponding record / row in database table. Now when persistent object turns to Transient object? this situation may arise normally when the record is deleted from the database. In this case there is no way the domain object in memory be mapped to any particular persistence context. * Note from Author: If anybody has any difference of opinion, please write it by replying to this question. Hibernate interview question 2 : Can you use final class as domain class for making the instances as persistent object? Hibernate interview answer : Yes, one can use final classes for instantiating to become persistent object. Hibernate interview question 3 : What is the difference between Java identity and Persistence entity from Hibernate perspective? Hibernate interview answer : While a domain object is in memory, then the equals() and hasCode() methods can be used for identifying domain object in memory, this way Java identity of domain object can be established. While Persistence identity is related to the primary key column and its value present in database table. Hibernate interview question 4 : Under what circumtances, is it required to implement equals and hasCode methods? Hibernate interview answer : There are two situations, where it is required that equals() and hasCode() methods should be implemented are as follows: 1. When there is one to many or many to one or many to many mapping, and the many part is contained in java.util.Set for holding all the mapped objects. As implementing class for Set interface, like java.util.HashSet uses equals and hasCode for operating certain methods like containsKey etc. 2. When any detached object is to be added back another Hibernate Session for converting the detached object to persistent object. Hibernate interview question 5 : Can you have a final class implementing an interface and use it with lazy="true" ? Hibernate interview answer : Yes, it is quite possible. * Note from Author: If anybody has any difference of opinion, please write it by replying to this question.

Hibernate Question : Can the strategy of LAZY load for the dependent domain classes, be change once SessionFactory is created? Answer to the Best of my knowledge: No, as SessionFactory is loaded/created once for the entire lifecycle of the application,and while creating Hibernate SessionFactory, appropriate HBM XML file is read and these configuration are used for creating or instantiating Hibernate SessionFactory, so it is logically not possible as, SessionFactory is not going to refresh but destroyed and recreated. And for different modules from the same application, if requires LAZY as true / false, then using a single Hibernate SessionFactory won't be able to serve both these Persistent Object loading strategies.

Hibernate Interview question : Is it possible to change LAZY loading strategy of persistent dependent object? Like changing Lazy value from true to false. Answer to the best of my knowledge on Hibernate No, while Hibernate SessionFactory is getting instantiated by using configuration parameters those are specified in HBM XML file, so once Hibernate SessionFactory is created, it will have to be destroyed and re-created to be able to take any changes in configuration, such as lazy value changed from true to false or vice versa.

Hibernate Question what are the differences between Projections and Restrictions in Hibernate? Answer to Hibernate Question In Hibernate, Projections can be used to manipulate groups functions, like in SQL we have group functions like COUNT, MAX, MIN, AVG, SUM, DISTINCT etc. While Restrictions can be used with conditional operations such as in SQL we have like, greater than (>), less than (<), equals to, in, between, is null or not null and many more.

Hibernate Question What is the difference between Component mapping and association mapping in Hibernate Mapping? Answer To the best of my understanding, Component mapping between two class files, such as for example company class file and department class file, can have a composition relationship. So this means that class department should be mapped within the company class definition. So this is the way component mapping is done, such as shown below: <class name="company" table="company"> .... .... <component name="department" class="Department"> .... .... <component> <class> One thing to note here that Department component mapping does not take table name as attribute, thus department class is not mapped as an Entity in component mapping. So attributes of company and department class files should have corresponding column defined in the common table, for example in this case it is company table. As Department is not having any independent identity in database, so this is not an Entity that can be deleted alone. If company Entity is deleted, then corresponding Department will be deleted as well. Thus Object-oriented composition relationship/notation among different objects can be achieved. But in case of association mapping, both the objects will have different class tags in Hibernate mapping file, and having different tables, and in this case these objects are having different identity and are Entities. This is one of the different I can remember as of now, if anyone having any comments on this, please write it here.

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