Explain about session interface
This represents hibernate session which perform the manipulation on the database entities. Some of the activities performed by session interface are as follows they are managing the persistence state, fetching persisted ones and management of the transaction demarcation.
What is Lazy Loading In Hibernate
Lazy setting decides whether to load child objects while loading the Parent Object.You need to do this setting respective hibernate mapping file of the parent class.lazy = true (means not to load child)By default the lazy loading of the child objects is true. This make sure that the child objects are not loaded unless they are explicitly invoked in the application by calling getChild()method on parent.In this case hibernate issues a fresh database call to load the child whengetChild() is actully called on the Parent object.But in some cases you do need to load the child objects when parent is loaded. Just make the lazy=false and hibernate will load the child when parent is loaded from the database.
Example: lazy=true (default)Address child of User class can be made lazy if it is not required frequently. lazy=false but you may need to load the Author object for Book parent whenever you deal with the book for online bookshop.
Lazy fetching means for example in hibernate if we use load() method then load() is lazy fetching i.e it is not going to touch the database until we write empobject.getString(eno); So when we write above statement in that instance it touch the database and get all the data from database. It is called as lazy loading.If we see another example i.e session.get(…) method is used then at that instance it is going to touch the database and get the data and place the data in session object it is called as eager loading.
How do you get an immutable collection
This functionality is provided by the Collections class, which is a wrapper implementation using the decorator design pattern.
public class ReadOnlyExample {
public static void main(String args[ ]) {
Set<string> set = new HashSet<string>( );
set.add(“Java”);
set.add(“JEE”);
set.add(“Spring”);
set.add(“Hibernate”);
set = Collections.unmodifiableSet(set);
set.add(“Ajax”); // not allowed.
}
}
Explain the steps involved in creating database applications with Java using Hibernate
Creating Database applications with Java is made simpler with Hibernate. First Plain old java object needs to be written, XML mapping file should be created which shows relationship between database and class attributes. Hibernate APIs can be used to store persistent objects.
Explain about Hibernate
Hibernate solves problems such as Object Relational impedance mismatch, etc. It is commonly used for object and query service. It helps data base developers develop classes which include inheritance, association, composition and polymorphism. A developer or user can express queries either in HQL or SQL
How does Hibernate distinguish between transient (i.e. newly instantiated) and detached objects
Hibernate uses the “version” property, if there is one.
If not uses the identifier value. No identifier value means a new object. This does work only for Hibernate managed surrogate keys. Does not work for natural keys and assigned (i.e. not managed by Hibernate) surrogate keys.
How will you configure Hibernate
The configuration files hibernate.cfg.xml (or hibernate.properties) and mapping files *.hbm.xml are used by the Configuration class to create (i.e. configure and bootstraphibernate) the SessionFactory, which in turn creates the Session instances. Session instances are the primary interface for the persistence service.hibernate.cfg.xml (alternatively can use hibernate.properties): These two files are used to configure the hibernate sevice (connection driver class, connection URL,connection username, connection password, dialect etc). If both files are present in the classpath then hibernate.cfg.xml file overrides the settings found in the hibernate.properties file.Mapping files (*.hbm.xml): These files are used to map persistent objects to a relational database. It is the best practice to store each object in an individual mapping file (i.e mapping file per class) because storing large number of persistent classes into one mapping file can be difficult to manage and maintain. The naming convention is to use the same name as the persistent (POJO) class name.
For example Account.class will have a mapping file named Account.hbm.xml. Alternatively, hibernate annotations can be used as part of your persistent class code instead of the *.hbm.xml files.
State some advantages of hibernate
Some of the advantages which a developer can get from Hibernate are as follows:
Mapping of one POJO table to one table is not required in hibernate.
It supports inheritance relationships and is generally a fast tool. Portability is necessary the greater benefit from hibernate. POJOs can be used in other applications where they are applicable.
Explain about hibernate.cfg.xml
Hibernate can be configured with two types of files out of which hibernate.cfg.xmlis widely used and popular feature. Hibernate consults hibernate.cfg.xml file for its operating properties such as database dialect, connection string and mapping files. These files are searched on class path.
Explain about the primary feature of Hibernate
Primary feature of hibernate is to java classes to database tables. Data query and retrieval is also possible with Hibernate. Application portability is a key feature in Hibernate it allows developers to port applications to almost all SQL databases.