A one-to-one mapping means one record in a table is linked to exactly one record in another table, such as one student and one student profile. In the database, one table holds a foreign key (here profile_id in students) that points to the other table, and a UNIQUE constraint makes sure it is never shared. […]
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An entity relationship describes how two tables are connected in the database, and JPA lets you show that connection as a link between two Java classes. A Student belongs to a Department, and a Department has many students. In the database this is a foreign key column (department_id) in the students table. In Java, you
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A native query is a plain SQL query, written with @Query(value = “…”, nativeQuery = true), that Spring Data sends to the database exactly as written. It uses real table and column names (students, marks), unlike JPQL, which uses entity and field names (Student, s.marks). It is used when JPQL is not suitable, such as
A custom query is a query you write yourself with the @Query annotation above a repository method, for needs that a method name alone cannot express. The default language is JPQL, which looks like SQL but uses entity and field names (Student, s.department) instead of table and column names. When you need database-specific SQL, you
A derived query method is a method you declare in a Spring Data repository interface, where Spring reads the method name and generates the SQL query for you. You write only the method signature, such as List<Student> findByDepartment(String department);, with no SQL and no method body. Spring splits the name into parts: the action (findBy),
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JPA Repository is a Spring Data JPA feature that provides ready-made database operations for JPA entities without requiring developers to write boilerplate SQL, JDBC connection, or EntityManager code. By extending JpaRepository, a repository interface automatically receives methods for common CRUD operations such as saving, retrieving, updating, and deleting records. Spring Data JPA creates the required
Entity Mapping is the process of mapping Java classes and their fields to relational database tables and columns using JPA annotations. A Java class is marked as an entity using @Entity, while @Table can be used to specify the database table name. The @Id annotation identifies the primary key, and @GeneratedValue can be used to
DatabaseMetaData is a JDBC interface used to obtain information about the database, JDBC driver, tables, columns, and supported database features. It is obtained from a Connection object using the getMetaData() method. Using DatabaseMetaData, a Java program can dynamically inspect database information without directly querying system tables. This is useful for database administration, debugging, database migration
Multiple database support means one Spring Boot application can run on different relational databases (H2, MySQL, PostgreSQL) without changing its Java code. Spring Boot picks the database from configuration: the driver on the classpath, the spring.datasource.* settings, and the active profile. Each database has its own settings file (application-h2.yml, application-mysql.yml, application-postgres.yml), and you switch between
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A database query returns rows of columns, but your Java code works with objects like Student. Row mapping is the step that converts each row into an object. In JdbcTemplate, a RowMapper does this: Spring runs the query, calls your mapper once per row, and collects the objects into a List. It is used so
