@Id and @GeneratedValue for primary keys in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to mark the primary key field in a Spring Boot entity.

Spring Boot

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

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

A@Id

B@Entity

C@Column

D@Table

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Entity instead of @Id for the primary key.

Forgetting to annotate the primary key field.

Using @Column or @Table which are for other purposes.

The @Id annotation marks the field as the primary key in a Spring Boot entity.

2fill in blank

medium

Complete the code to automatically generate the primary key value.

Spring Boot

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

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

A@Transient

B@Column(nullable = false)

C@Table(name = "users")

D@GeneratedValue(strategy = GenerationType.AUTO)

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Column instead of @GeneratedValue for key generation.

Omitting the strategy parameter.

Using @Transient which excludes the field from persistence.

The @GeneratedValue annotation with strategy AUTO tells Spring Boot to generate the primary key automatically.

3fill in blank

hard

Fix the error in the code to correctly generate the primary key using identity strategy.

Spring Boot

public class Product {
    @Id
    @GeneratedValue(strategy = [1])
    private Long productId;
}

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

AGenerationType.IDENTITY

BGenerationType.AUTO

CGenerationType.SEQUENCE

DGenerationType.TABLE

Attempts:

3 left

💡 Hint

Common Mistakes

Using AUTO instead of IDENTITY when the database requires identity strategy.

Confusing SEQUENCE with IDENTITY.

Omitting the strategy parameter.

GenerationType.IDENTITY tells Spring Boot to use the database identity column for key generation.

4fill in blank

hard

Fill both blanks to define a primary key with sequence generation in a Spring Boot entity.

Spring Boot

public class Order {
    @Id
    @GeneratedValue(strategy = [1], generator = [2])
    private Long orderId;
}

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

AGenerationType.SEQUENCE

B"order_seq"

CGenerationType.IDENTITY

D"seq_order"

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing IDENTITY with sequence generator name.

Using generator name without quotes.

Using wrong GenerationType for sequence.

Use GenerationType.SEQUENCE for sequence strategy and specify the sequence generator name as a string.

5fill in blank

hard

Fill all three blanks to define a primary key with sequence generation and sequence generator annotation.

Spring Boot

public class Invoice {
    @Id
    @SequenceGenerator(name = [1], sequenceName = [2], allocationSize = 1)
    @GeneratedValue(strategy = [3], generator = [1])
    private Long invoiceId;
}

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

A"invoice_seq"

B"seq_invoice"

CGenerationType.SEQUENCE

DGenerationType.IDENTITY

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for generator and sequence generator.

Using IDENTITY strategy with sequence generator.

Omitting quotes around string names.

The sequence generator name is "invoice_seq", the sequence name is "seq_invoice", and the strategy is GenerationType.SEQUENCE.

Practice

1. What is the main purpose of the @Id annotation in a Spring Boot entity?

easy

A. To specify a foreign key relationship

B. To generate unique values automatically

C. To define a database table name

D. To mark the primary key field of the entity

Solution

1. Step 1: Understand the role of @Id

   The @Id annotation marks a field as the primary key in a database entity.

2. Step 2: Differentiate from other annotations

   @GeneratedValue generates values, but @Id specifically identifies the primary key field.

3. Final Answer:

   To mark the primary key field of the entity -> Option D

4. Quick Check:

   @Id marks primary key [OK]

Hint: Remember: @Id means 'this is the primary key' [OK]

Common Mistakes:

• Confusing @Id with @GeneratedValue
• Thinking @Id generates values automatically
• Using @Id to name tables

2. Which of the following is the correct way to use @GeneratedValue with GenerationType.IDENTITY in a Spring Boot entity?

easy

A. @GeneratedValue(strategy = GenerationType.AUTO)

B. @GeneratedValue(strategy = GenerationType.SEQUENCE)

C. @GeneratedValue(strategy = GenerationType.IDENTITY)

D. @GeneratedValue(strategy = GenerationType.TABLE)

Solution

1. Step 1: Identify the correct strategy for identity generation

   GenerationType.IDENTITY is used to let the database auto-increment the primary key.

2. Step 2: Match the annotation syntax

   The correct syntax is @GeneratedValue(strategy = GenerationType.IDENTITY).

3. Final Answer:

   @GeneratedValue(strategy = GenerationType.IDENTITY) -> Option C

4. Quick Check:

   Use GenerationType.IDENTITY with strategy = GenerationType.IDENTITY [OK]

Hint: Use strategy = GenerationType.IDENTITY for auto-increment keys [OK]

Common Mistakes:

• Using AUTO instead of IDENTITY for auto-increment
• Omitting the strategy parameter
• Confusing SEQUENCE with IDENTITY

3. Given the entity code below, what will be the value of user.getId() after saving a new user to the database?

 @Entity
 public class User {
   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   private Long id;
   private String name;

   // getters and setters
 }

medium

A. A unique auto-generated Long value

B. null

C. The name of the user

D. An exception will be thrown

Solution

1. Step 1: Understand @GeneratedValue with IDENTITY

   This strategy lets the database generate a unique primary key value automatically when saving.

2. Step 2: Predict the value after saving

   After saving, user.getId() will hold the generated unique Long value assigned by the database.

3. Final Answer:

   A unique auto-generated Long value -> Option A

4. Quick Check:

   @GeneratedValue with IDENTITY creates unique IDs [OK]

Hint: After save, IDENTITY generates a unique Long ID automatically [OK]

Common Mistakes:

• Expecting id to be null after save
• Confusing id with other fields
• Assuming an error occurs without database setup

4. Consider this entity code snippet:

 @Entity
 public class Product {
   @Id
   @GeneratedValue
   private Long productId;

   private String name;
 }

What is the likely problem with this code?

medium

A. Missing strategy in @GeneratedValue may cause unexpected ID generation

B. The field productId should not be private

C. The @Id annotation is missing

D. The entity class must implement Serializable

Solution

1. Step 1: Check @GeneratedValue usage

   The @GeneratedValue annotation without specifying a strategy defaults to AUTO, which may behave differently depending on the database.

2. Step 2: Understand impact of missing strategy

   This can cause unexpected ID generation behavior if the database does not support the default strategy well.

3. Final Answer:

   Missing strategy in @GeneratedValue may cause unexpected ID generation -> Option A

4. Quick Check:

   Always specify strategy to avoid surprises [OK]

Hint: Always specify strategy in @GeneratedValue to avoid surprises [OK]

Common Mistakes:

• Thinking private fields cause errors
• Believing @Id is missing
• Assuming Serializable is mandatory

5. You want to create a Spring Boot entity with a primary key that uses a database sequence named user_seq. Which is the correct way to annotate the ID field?

hard

A. @Id @GeneratedValue(strategy = GenerationType.IDENTITY)

B. @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "user_seq") @SequenceGenerator(name = "user_seq", sequenceName = "user_seq", allocationSize = 1)

C. @Id @GeneratedValue(strategy = GenerationType.TABLE)

D. @Id @GeneratedValue(strategy = GenerationType.AUTO)

Solution

1. Step 1: Identify sequence generation requirements

   Using a database sequence requires GenerationType.SEQUENCE and a matching @SequenceGenerator annotation.

2. Step 2: Match annotations to sequence name

   The @SequenceGenerator defines the sequence name and allocation size, linked by the generator name in @GeneratedValue.

3. Final Answer:

   @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "user_seq") @SequenceGenerator(name = "user_seq", sequenceName = "user_seq", allocationSize = 1) -> Option B

4. Quick Check:

   Use SEQUENCE with @SequenceGenerator for DB sequences [OK]

Hint: Use @SequenceGenerator with SEQUENCE strategy for DB sequences [OK]

Common Mistakes:

• Using IDENTITY instead of SEQUENCE for sequences
• Omitting @SequenceGenerator annotation
• Confusing TABLE and AUTO strategies