Overview of JPA and in-depth explanation of common annotations.
JPA (Java Persistence API) is a part of the Java persistence specification, which offers a way to access, manage, and persist Java objects into a relational database. It simplifies the tasks of developers in persisting data by providing a standardized set of APIs and annotations, making database operations easier and more convenient for developers.
Common annotations:
- @Entity: Used to map Java classes to database tables. Classes marked with this annotation will be recognized by the JPA framework as entity classes, and the properties of this class will be mapped to fields in the database table.
- @Table: Specifies the name of the database table and other attributes corresponding to the entity class. It can specify the table’s name, indexes, constraints, and so on.
- @Id: Used to define the primary key field of an entity class. It can be used on a property or a getter method.
- @GeneratedValue is used to define the strategy for generating primary keys. It can specify strategies such as auto-incrementing or using UUID for primary keys.
- @Column: is used to define the mapping relationship between entity class attributes and database table fields. It can specify the field’s name, length, constraints, and more.
- @Transient: Used to specify that a certain property does not need to be persisted in the database. Properties marked with this annotation will not be stored in the database by the JPA framework.
- @OneToMany: Used to define a one-to-many relationship. A property marked with this annotation indicates a relationship between one entity class and multiple other entity classes.
- @ManyToOne: Used to define a many-to-one relationship, where a property marked with this annotation indicates a relationship between one entity class and another entity class.
- @OneToOne is used to define a one-to-one relationship. The property marked with this annotation represents a relationship between one entity class and another entity class.
- @ManyToMany: Used to define a many-to-many relationship. An attribute marked with this annotation represents a relationship between an entity class and multiple other entity classes.
These annotations can assist developers in simplifying database operation code, thereby improving development efficiency. Additionally, JPA also offers a range of query operations that can be used for database querying through annotations or JPQL (Java Persistence Query Language).
