JPA entity with @Entity annotation in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a JPA entity class with the correct annotation.

Spring Boot

import jakarta.persistence.[1];

@[1]
public class User {
    private Long id;
    private String name;
}

Drag options to blanks, or click blank then click option'

AEntity

BTable

CColumn

DId

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Table instead of @Entity

Forgetting to import the annotation

Using @Id instead of @Entity

The @Entity annotation marks the class as a JPA entity, which means it maps to a database table.

2fill in blank

medium

Complete the code to mark the primary key field with the correct annotation.

Spring Boot

import jakarta.persistence.Entity;
import jakarta.persistence.[1];

@Entity
public class Product {
    @[1]
    private Long id;
    private String name;
}

Drag options to blanks, or click blank then click option'

ATable

BColumn

CGeneratedValue

DId

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Column instead of @Id

Not annotating the primary key field

Using @Table on a field

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

3fill in blank

hard

Fix the error in the code by choosing the correct annotation to generate the primary key value automatically.

Spring Boot

import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import jakarta.persistence.[1];

@Entity
public class Order {
    @Id
    @[1]
    private Long id;
    private String product;
}

Drag options to blanks, or click blank then click option'

AColumn

BTable

CGeneratedValue

DEntity

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Column instead of @GeneratedValue

Forgetting to add @GeneratedValue for auto-generation

Using @Table on a field

The @GeneratedValue annotation tells JPA to generate the primary key value automatically.

4fill in blank

hard

Fill both blanks to complete the JPA entity with a primary key and a column annotation.

Spring Boot

import jakarta.persistence.Id;
import jakarta.persistence.[1];
import jakarta.persistence.[2];

@[1]
public class Customer {
    @Id
    private Long id;
    @[2](name = "customer_name")
    private String name;
}

Drag options to blanks, or click blank then click option'

AEntity

BTable

CColumn

DId

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Table instead of @Entity

Using @Id instead of @Column on the name field

Forgetting to import the annotations

@Entity marks the class as a JPA entity. @Column customizes the mapping of the field to the database column.

5fill in blank

hard

Fill all three blanks to complete the JPA entity with @Entity, @Id, and @GeneratedValue annotations.

Spring Boot

import jakarta.persistence.[1];
import jakarta.persistence.[2];
import jakarta.persistence.[3];

@[1]
public class Invoice {
    @[2]
    @[3]
    private Long id;
    private Double amount;
}

Drag options to blanks, or click blank then click option'

AEntity

BId

CGeneratedValue

DColumn

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up @Column with @Id or @GeneratedValue

Forgetting to annotate the primary key

Not importing the correct annotations

@Entity marks the class as a JPA entity. @Id marks the primary key field. @GeneratedValue tells JPA to generate the key automatically.

Practice

1. What is the main purpose of the @Entity annotation in a Spring Boot application?

easy

A. To mark a class as a database table for JPA

B. To create a REST API endpoint

C. To configure application properties

D. To define a service component

Solution

1. Step 1: Understand the role of @Entity

   The @Entity annotation tells Spring Boot and JPA that this class represents a table in the database.

2. Step 2: Differentiate from other annotations

   Other annotations like @RestController or @Service serve different purposes unrelated to database tables.

3. Final Answer:

   To mark a class as a database table for JPA -> Option A

4. Quick Check:

   @Entity marks database tables [OK]

Hint: Remember: @Entity means database table class [OK]

Common Mistakes:

• Confusing @Entity with @Service
• Thinking @Entity creates REST endpoints
• Assuming @Entity configures app settings

2. Which of the following is the correct way to declare a JPA entity class with an ID field?

easy

A. @Entity public class User { private Long id; }

B. public class User { private Long id; }

C. @Entity public class User { @Id private Long id; }

D. @Service public class User { @Id private Long id; }

Solution

1. Step 1: Check for @Entity annotation

   The class must have @Entity to be recognized as a JPA entity.

2. Step 2: Verify presence of @Id on a field

   Every entity needs a unique identifier marked with @Id to map the primary key.

3. Final Answer:

   @Entity public class User { @Id private Long id; } -> Option C

4. Quick Check:

   Entity + Id field = correct syntax [OK]

Hint: Entity needs @Entity and @Id on ID field [OK]

Common Mistakes:

• Missing @Entity annotation
• Forgetting @Id on the ID field
• Using @Service instead of @Entity

3. Given this entity class:

@Entity
public class Product {
  @Id
  private Long id;
  private String name;

  public Product() {}
  public Product(Long id, String name) {
    this.id = id;
    this.name = name;
  }
  public String getName() { return name; }
}

What will happen if you save a Product with id=1 and name="Book" using JPA repository and then retrieve it?

medium

A. The Product is not saved because of missing @Column

B. You get a Product object with id=1 and name="Book"

C. You get a runtime error because no setter for name

D. You get a Product object with id=1 but name is null

Solution

1. Step 1: Understand JPA entity saving and retrieval

   JPA uses the @Entity class and its fields to save and load data. The constructor and getter allow access to fields.

2. Step 2: Check if missing setter affects retrieval

   JPA can set fields via reflection even without setters, so name will be loaded correctly.

3. Final Answer:

   You get a Product object with id=1 and name="Book" -> Option B

4. Quick Check:

   JPA loads fields even without setters [OK]

Hint: JPA sets fields directly; getters needed to read [OK]

Common Mistakes:

• Assuming missing setter causes runtime error
• Thinking @Column is mandatory for saving
• Believing name will be null without setter

4. Identify the error in this entity class:

@Entity
public class Customer {
  private Long id;
  private String email;

  public Long getId() { return id; }
  public String getEmail() { return email; }
}

medium

A. Missing @Entity annotation

B. Missing default constructor

C. Fields should be public

D. Missing @Id annotation on the id field

Solution

1. Step 1: Check for @Entity annotation

   The class has @Entity, so it is recognized as an entity.

2. Step 2: Verify presence of @Id annotation

   The id field lacks @Id, so JPA cannot identify the primary key, causing errors.

3. Final Answer:

   Missing @Id annotation on the id field -> Option D

4. Quick Check:

   Every entity needs @Id on primary key [OK]

Hint: Always put @Id on the primary key field [OK]

Common Mistakes:

• Assuming default constructor is mandatory (JPA provides one)
• Thinking fields must be public
• Ignoring missing @Id annotation

5. You want to create a JPA entity Order with a composite primary key made of orderId and productId. Which approach correctly applies the @Entity annotation and primary key setup?

hard

A. Use @Entity on Order and create a separate @Embeddable class for the composite key with @EmbeddedId in Order

B. Use @Entity on Order and mark both fields @Id without extra class

C. Use @Entity on Order and mark only one field @Id, ignore the other

D. Use @Entity on Order and define composite key in application.properties

Solution

1. Step 1: Understand composite keys in JPA

   JPA requires a separate class annotated with @Embeddable to represent composite keys.

2. Step 2: Use @EmbeddedId in the entity

   The entity class uses @EmbeddedId to include the composite key class as its primary key.

3. Final Answer:

   Use @Entity on Order and create a separate @Embeddable class for the composite key with @EmbeddedId in Order -> Option A

4. Quick Check:

   Composite key needs @Embeddable + @EmbeddedId [OK]

Hint: Composite keys need @Embeddable class + @EmbeddedId field [OK]

Common Mistakes:

• Marking multiple fields with @Id without composite key class
• Ignoring one key field in composite key
• Trying to configure keys in properties file