Hibernate mapping is a core part of Object-Relational Mapping (ORM), which defines the relationships between Java objects (entities) and database tables to enable seamless communication between them. Here are some of the main uses of hibernate mapping.
1. Entity Persistence: Mapping allows Java classes to be marked as persistent entities using annotations or XML definitions. These items can be stored, retrieved, updated and deleted from the database without writing raw SQL queries.
2. Database Schema Creation: Hibernate can automatically create a database schema based on entity. This simplifies database installation and maintenance because developers do not have to manually create tables.
3. Column Mapping: You can specify how individual fields or properties of Java classes are mapped to database columns. This includes data types, constraints, and naming conventions. For example, you can map a Java string field to a VARCHAR database column.
. 4.Primary Key Generation: Hibernate provides mechanisms to generate primary key values, such as auto-incrementing values or sequences that can be defined using mappings.
5. Mapping relationships: You can use mapping to define relationships between entities, such as one-to-one, one-to-many ,many-to-many & many-to-one. This allows Hibernate to manage foreign-key constraints and simplify relational data queries.
6.Inheritance Mapping: Hibernate supports various inheritance strategies (eg, single table, join, table-by-table hierarchy) to map Java class hierarchies to database tables. It allows modelling complex class structures.
7. Lazy Loading: A map can configure lazy loading of related entities, improving performance by loading data only when it is actually being used.
8. Custom Queries: Mapping can define custom SQL queries or Hibernate Query Language (HQL) queries for complex database operations.
9. Caching: Hibernate can be configured to cache objects and queries, reducing the number of database queries and improving application performance.
10. Validation and Constraints: The mapping can include validation rules and data integrity constraints at the application level, ensuring that only valid data is stored.
Hibernate offers the following mapping types.
@OneToOne Mapping
One-to-one mapping in hibernate framework is a way to create a connection between two entities in a database so that one entity maps to exactly one instance of another entity. Both entities can connect unidirectionally or bidirectionally. we can treat it as a special relationship where each entity has a unique partner. You can create a one-to-one mapping in Hibernate using the @OneToOne annotation.
Imagine you have two tables in a database: Question and Answer. Each Question has only one Answer, and each Answer belongs to only one Question. This is called one-to-one relationship.
@OneToMany Mapping
In one-to-many mapping one entity is associated with multiple instances of another entity. It is mostly used to model a parent-child or master-detail relationship in a database. You can create a one-to-many mapping in Hibernate using the @OneToMany annotation.
For example, suppose we have two entities: Employee and Department. Each Department can have multiple Employees, but each Employee belongs to only one Department.
@ManytoMany
a many-to-many mapping represents a relationship between two entities, where each entity can be associated with multiple instances of the other entity. In a many-to-many relationship between two tables, an intermediate table (common table) that stores the relationship between the two entities.
Hibernate create a junction table (intermediary table) while establishing many-to-many relationship between two entities & this junction table store the relationship between two entities. You can create a many-to-many mapping in Hibernate using the @ManyToMany annotation.
In summary, Hibernate mapping is necessary to define the structure, relationships and behaviour of Java objects in a relational database context. It abstracts the complexity of database interaction, making it easy to use databases in Java applications.
