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18 Cards in this Set
- Front
- Back
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What is ORM ?
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ORM stands for object/relational mapping. ORM is the automated persistence of objects in a Java application to the tables in a relational database.
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What does ORM consists of ?
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* API for performing basic CRUD operations
* API to express quries refering to classes * Facilities to specify metadata * Optimization facilities : dirty checking,lazy associations fetching |
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What is Hibernate?
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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.
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What is the need for Hibernate xml mapping file?
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Hibernate mapping file tells Hibernate which tables and columns to use to load and store objects.
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What are the most common methods of Hibernate configuration?
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* Programmatic configuration
* XML configuration (hibernate.cfg.xml) |
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What are the important tags of hibernate.cfg.xml?
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* JDBC connection configuration
* SQL variant to generate * Size of connection pool * Automation generation of schema * Mapping files |
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What are the Core interfaces are of Hibernate framework?
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* Session interface
* SessionFactory interface * Configuration interface * Transaction interface * Query and Criteria interfaces |
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What role does the Session interface play in Hibernate?
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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.
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What role does the SessionFactory interface play in Hibernate?
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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.
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How do you map Java Objects with Database tables?
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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. |
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How do you define sequence generated primary key in hibernate?
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Using <generator> tag.
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Define HibernateTemplate?
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org.springframework.orm.hibernate.HibernateTemplate is a helper class which provides different methods for querying/retrieving data from the database. It also converts checked HibernateExceptions into unchecked DataAccessExceptions.
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How do you switch between relational databases without code changes?
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Using Hibernate SQL Dialects , we can switch databases. Hibernate will generate appropriate hql queries based on the dialect defined.
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What are derived properties?
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The properties that are not mapped to a column, but calculated at runtime by evaluation of an expression are called derived properties. The expression can be defined using the formula attribute of the element.
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What is component mapping in Hibernate?
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* A component is an object saved as a value, not as a reference
* A component can be saved directly without needing to declare interfaces or identifier properties * Required to define an empty constructor * Shared references not supported |
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What do you mean by fetching strategy ?
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A fetching strategy is the strategy Hibernate will use for retrieving associated objects if the application needs to navigate the association. Fetch strategies may be declared in the O/R mapping metadata, or over-ridden by a particular HQL or Criteria query.
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What is automatic dirty checking?
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Automatic dirty checking is a feature that saves us the effort of explicitly asking Hibernate to update the database when we modify the state of an object inside a transaction.
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What are the types of inheritance models in Hibernate?
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* Table per class hierarchy
* Table per subclass * Table per concrete class |
