@Id and @GeneratedValue for primary keys in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the @Id annotation in Spring Boot?

The @Id annotation marks a field as the primary key of an entity. It tells Spring Boot which field uniquely identifies each record in the database.

beginner

What does the @GeneratedValue annotation do?

The @GeneratedValue annotation tells Spring Boot to automatically generate a value for the primary key when saving a new entity. It helps avoid manually setting unique IDs.

intermediate

Which strategy options can you use with @GeneratedValue?

Common strategies include AUTO (default, lets the provider choose), IDENTITY (database auto-increment), SEQUENCE (uses a database sequence), and TABLE (uses a table to generate IDs).

beginner

Why is it important to use @Id and @GeneratedValue together?

Using @Id identifies the primary key field, and @GeneratedValue automates its value creation. Together, they ensure each entity has a unique, automatically assigned ID.

beginner

Show a simple example of an entity with @Id and @GeneratedValue annotations.

Example:
<pre>
@Entity
public class User {
  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Long id;
  private String name;
  // getters and setters
}</pre>

What does the @Id annotation specify in a Spring Boot entity?

A The primary key field

B A foreign key field

C A regular column

D A database table name

The @Id annotation marks the field as the primary key of the entity.

Which annotation automatically generates the primary key value?

A @GeneratedValue

B @Column

C @Entity

D @Table

@GeneratedValue tells Spring Boot to generate the primary key value automatically.

What is the default strategy for @GeneratedValue if none is specified?

A IDENTITY

B AUTO

C SEQUENCE

D TABLE

AUTO lets the persistence provider choose the best strategy automatically.

Which strategy uses a database sequence to generate IDs?

A IDENTITY

B AUTO

C SEQUENCE

D TABLE

SEQUENCE uses a database sequence object to generate unique IDs.

Why should you not manually assign values to a field annotated with @GeneratedValue?

A Because the field is read-only

B Because the database will ignore manual values

C Because it will cause duplicate keys

D Because the value is automatically generated and manual assignment can cause errors

Manual assignment can conflict with automatic generation and cause errors.

Explain how @Id and @GeneratedValue work together in a Spring Boot entity.

Think about how the database knows which field is the unique identifier and how it gets its value.

Describe the different strategies available for @GeneratedValue and when you might use each.

Consider how different databases handle ID generation.