1. What is ORM?
ORM stands for object/relational mapping. ORM is the automated persistence of objects in a Java application to the tables in a relational database.
2. What does ORM consists of?
An ORM solution consists of the following four pieces:
v It should have an API for performing basic CRUD (Create, Read, Update, Delete) operations on objects of persistent classes
v Should have a language or an API for specifying queries that refer to the classes and the properties of classes
v Ability for specifying mapping metadata
v It should have a technique for ORM implementation to interact with transactional objects to perform dirty checking, lazy association fetching, and other optimization functions
3. What are the ORM levels?
The ORM levels are:
* Pure relational (stored procedure.)
* Light objects mapping (JDBC)
* Medium object mapping
* Full object Mapping (composition, inheritance, polymorphism, persistence by reachability)
4. What is Hibernate?
Hibernate is a pure Java object-relational mapping (ORM) and persistence framework that allows you to map plain old Java objects to relational database tables using (XML) configuration files. Its purpose is to relieve the developer from a significant amount of relational data persistence-related programming tasks.
5. Why do you need ORM tools like hibernate?
The main advantage of ORM like hibernate is that it shields developers from messy SQL. Apart from this, ORM provides following benefits:
* Improved productivity
6. What Does Hibernate Simplify?
Hibernate simplifies:
* Saving and retrieving your domain objects
* Making database column and table name changes
* Centralizing pre save and post retrieve logic
* Complex joins for retrieving related items
* Schema creation from object model
7. What is the need for Hibernate xml mapping file?
Hibernate mapping file tells Hibernate which tables and columns to use to load and store objects.
8. What are the most common methods of Hibernate configuration?
The most common methods of Hibernate configuration are:
* Programmatic configuration
* XML configuration (hibernate.cfg.xml)
9. What are the Core interfaces are of Hibernate framework?
The five core interfaces are used in just about every Hibernate application. Using these interfaces, you can store and retrieve persistent objects and control transactions.
* Session interface
* SessionFactory interface
* Configuration interface
* Transaction interface
* Query and Criteria interfaces
10. What role does the Session interface play in Hibernate?
The Session interface is the primary interface used by Hibernate applications. It is a single-threaded, short-lived object representing a conversation between the application and the persistent store. It allows you to create query objects to retrieve persistent objects.
Session session = sessionFactory.openSession();
Session interface role:
* Wraps a JDBC connection
* Factory for Transaction
* Holds a mandatory (first-level) cache of persistent objects, used when navigating the object graph or looking up objects by identifier
11. What are the important tags of hibernate.cfg.xml?
12. What role does the SessionFactory interface play in Hibernate?
The application obtains Session instances from a SessionFactory. There is typically a single SessionFactory for the whole application—created during application initialization. The SessionFactory caches generate SQL statements and other mapping metadata that Hibernate uses at runtime. It also holds cached data that has been read in one unit of work and may be reused in a future unit of work
SessionFactory sessionFactory = configuration.buildSessionFactory();
13. What is the general flow of Hibernate communication with RDBMS?
The general flow of Hibernate communication with RDBMS is:
* Load the Hibernate configuration file and create configuration object. It will automatically load all hbm mapping files
* Create session factory from configuration object
* Get one session from this session factory
* Create HQL Query
* Execute query to get list containing Java objects
14. What is Hibernate Query Language (HQL)?
Hibernate offers a query language that embodies a very powerful and flexible mechanism to query, store, update, and retrieve objects from a database. This language, the Hibernate query Language (HQL), is an object-oriented extension to SQL.
15. How do you map Java Objects with Database tables?
* First we need to write Java domain objects (beans with setter and getter). The variables should be same as database columns.
* Write hbm.xml, where we map java class to table and database columns to Java class variables.
<hibernate-mapping>
<class name="com.test.User" table="user">
<property column="USER_NAME" length="255"
name="userName" not-null="true" type="java.lang.String"/>
<property column="USER_PASSWORD" length="255"
name="userPassword" not-null="true" type="java.lang.String"/>
</class>
</hibernate-mapping>
16. What’s the difference between load() and get()?
load() vs. get() :-
<return-property name="address" column="EMP_ADDRESS"/>
{ ? = call selectAllEmployees() } </return>
</sql-query>
ORM stands for object/relational mapping. ORM is the automated persistence of objects in a Java application to the tables in a relational database.
2. What does ORM consists of?
An ORM solution consists of the following four pieces:
v It should have an API for performing basic CRUD (Create, Read, Update, Delete) operations on objects of persistent classes
v Should have a language or an API for specifying queries that refer to the classes and the properties of classes
v Ability for specifying mapping metadata
v It should have a technique for ORM implementation to interact with transactional objects to perform dirty checking, lazy association fetching, and other optimization functions
3. What are the ORM levels?
The ORM levels are:
* Pure relational (stored procedure.)
* Light objects mapping (JDBC)
* Medium object mapping
* Full object Mapping (composition, inheritance, polymorphism, persistence by reachability)
4. What is Hibernate?
Hibernate is a pure Java object-relational mapping (ORM) and persistence framework that allows you to map plain old Java objects to relational database tables using (XML) configuration files. Its purpose is to relieve the developer from a significant amount of relational data persistence-related programming tasks.
5. Why do you need ORM tools like hibernate?
The main advantage of ORM like hibernate is that it shields developers from messy SQL. Apart from this, ORM provides following benefits:
* Improved productivity
o High-level object-oriented API
o Less Java code to write
o No SQL to write
* Improved performance o Sophisticated caching
o Lazy loading
o Eager loading
* Improved maintainability o A lot less code to write
* Improved portability o ORM framework generates database-specific SQL for you
6. What Does Hibernate Simplify?
Hibernate simplifies:
* Saving and retrieving your domain objects
* Making database column and table name changes
* Centralizing pre save and post retrieve logic
* Complex joins for retrieving related items
* Schema creation from object model
7. What is the need for Hibernate xml mapping file?
Hibernate mapping file tells Hibernate which tables and columns to use to load and store objects.
8. What are the most common methods of Hibernate configuration?
The most common methods of Hibernate configuration are:
* Programmatic configuration
* XML configuration (hibernate.cfg.xml)
9. What are the Core interfaces are of Hibernate framework?
The five core interfaces are used in just about every Hibernate application. Using these interfaces, you can store and retrieve persistent objects and control transactions.
* Session interface
* SessionFactory interface
* Configuration interface
* Transaction interface
* Query and Criteria interfaces
10. What role does the Session interface play in Hibernate?
The Session interface is the primary interface used by Hibernate applications. It is a single-threaded, short-lived object representing a conversation between the application and the persistent store. It allows you to create query objects to retrieve persistent objects.
Session session = sessionFactory.openSession();
Session interface role:
* Wraps a JDBC connection
* Factory for Transaction
* Holds a mandatory (first-level) cache of persistent objects, used when navigating the object graph or looking up objects by identifier
11. What are the important tags of hibernate.cfg.xml?
12. What role does the SessionFactory interface play in Hibernate?
The application obtains Session instances from a SessionFactory. There is typically a single SessionFactory for the whole application—created during application initialization. The SessionFactory caches generate SQL statements and other mapping metadata that Hibernate uses at runtime. It also holds cached data that has been read in one unit of work and may be reused in a future unit of work
SessionFactory sessionFactory = configuration.buildSessionFactory();
13. What is the general flow of Hibernate communication with RDBMS?
The general flow of Hibernate communication with RDBMS is:
* Load the Hibernate configuration file and create configuration object. It will automatically load all hbm mapping files
* Create session factory from configuration object
* Get one session from this session factory
* Create HQL Query
* Execute query to get list containing Java objects
14. What is Hibernate Query Language (HQL)?
Hibernate offers a query language that embodies a very powerful and flexible mechanism to query, store, update, and retrieve objects from a database. This language, the Hibernate query Language (HQL), is an object-oriented extension to SQL.
15. How do you map Java Objects with Database tables?
* First we need to write Java domain objects (beans with setter and getter). The variables should be same as database columns.
* Write hbm.xml, where we map java class to table and database columns to Java class variables.
<hibernate-mapping>
<class name="com.test.User" table="user">
<property column="USER_NAME" length="255"
name="userName" not-null="true" type="java.lang.String"/>
<property column="USER_PASSWORD" length="255"
name="userPassword" not-null="true" type="java.lang.String"/>
</class>
</hibernate-mapping>
16. What’s the difference between load() and get()?
load() vs. get() :-
load() | get() |
Only use the load() method if you are sure that the object exists. | If you are not sure that the object exists, then use one of the get() methods. |
load() method will throw an exception if the unique id is not found in the database. | get() method will return null if the unique id is not found in the database. |
load() just returns a proxy by default and database won’t be hit until the proxy is first invoked. | get() will hit the database immediately. |
17.What is the difference between and merge and update ?
Use update() if you are sure that the session does not contain an already persistent instance with the same identifier, and merge() if you want to merge your modifications at any time without consideration of the state of the session.
18. How do you define sequence generated primary key in hibernate?
Using <generator> tag.
<id column="USER_ID" name="id" type="java.lang.Long">
<generator class="sequence">
<param name="table">SEQUENCE_NAME</param>
<generator>
</id>
<generator class="sequence">
<param name="table">SEQUENCE_NAME</param>
<generator>
</id>
19. Define cascade and inverse option in one-many mapping?
cascade - enable operations to cascade to child entities.
cascade="all|none|save-update|delete|all-delete-orphan"
inverse - mark this collection as the "inverse" end of a bidirectional association.
inverse="true|false"
Essentially "inverse" indicates which end of a relationship should be ignored, so when persisting a parent who has a collection of children, should you ask the parent for its list of children, or ask the children who the parents are?
20. What does it mean to be inverse?
It informs hibernate to ignore that end of the relationship. If the one–to–many was marked as inverse, hibernate would create a child–>parent relationship (child.getParent). If the one–to–many was marked as non–inverse then a child–>parent relationship would be created.
21. What do you mean by Named – SQL query?
Named SQL queries are defined in the mapping xml document and called wherever required.
Example:
<sql-query name = "empdetails">
<return alias="emp" class="com.test.Employee"/>
SELECT emp.EMP_ID AS {emp.empid},
emp.EMP_ADDRESS AS {emp.address},
emp.EMP_NAME AS {emp.name}
FROM Employee EMP WHERE emp.NAME LIKE :name
</sql-query>
<return alias="emp" class="com.test.Employee"/>
SELECT emp.EMP_ID AS {emp.empid},
emp.EMP_ADDRESS AS {emp.address},
emp.EMP_NAME AS {emp.name}
FROM Employee EMP WHERE emp.NAME LIKE :name
</sql-query>
Invoke Named Query:
List people = session.getNamedQuery("empdetails")
.setString("TomBrady", name)
.setMaxResults(50)
.list();
22. How do you invoke Stored Procedures?
<sql-query name="selectAllEmployees_SP" callable="true">
<return alias="emp" class="employee">
<return-property name="empid" column="EMP_ID"/>
<return-property name="name" column="EMP_NAME"/> <return alias="emp" class="employee">
<return-property name="empid" column="EMP_ID"/>
<return-property name="address" column="EMP_ADDRESS"/>
{ ? = call selectAllEmployees() } </return>
</sql-query>
Posts
0 comments:
Post a Comment