Custom query methods by naming convention in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Spring Data JPA method return?

Given the method List findByAgeGreaterThan(int age); in a repository interface, what will it return when called with findByAgeGreaterThan(30)?

A All users with age less than 30

B All users with age exactly 30

C All users with age greater than 30

D All users with age greater than or equal to 30

💡 Hint

Think about the meaning of 'GreaterThan' in the method name.

The method name 'findByAgeGreaterThan' tells Spring Data JPA to find all users whose age is strictly greater than the given value.

📝 Syntax

intermediate

Which method signature is valid for finding users by last name and active status?

You want to create a method in a Spring Data JPA repository to find users by their last name and whether they are active. Which method signature is valid?

A List<User> findByLastName_And_Active(String lastName, boolean active);

B List<User> findByLastNameAndActive(String lastName, boolean active);

C List<User> findByLastNameActive(String lastName, boolean active);

D List<User> findByLastNameOrActive(String lastName, boolean active);

💡 Hint

Use 'And' to combine conditions in method names.

Spring Data JPA supports 'And' and 'Or' keywords to combine conditions. The method name must follow camel case with these keywords.

🔧 Debug

advanced

Why does this method cause a runtime error?

Consider this method in a Spring Data JPA repository:
List findByEmailContainingIgnoreCaseOrderByAgeDesc(String emailPart);
At runtime, calling this method causes an error. What is the most likely cause?

A The method name is valid but the entity does not have an 'age' field

B The method name is too long and exceeds Spring Data limits

C The method name uses unsupported keywords 'ContainingIgnoreCase' and 'OrderBy' together

D The method should return a single User, not a list

💡 Hint

Check if all fields in the method name exist in the entity.

If the entity lacks the 'age' field, Spring Data cannot create the query and throws an error at runtime.

🧠 Conceptual

advanced

What is the effect of using 'Distinct' in method names?

In Spring Data JPA, what does adding 'Distinct' to a query method name do?
For example: List findDistinctByCity(String city);

A It removes duplicate users from the result list

B It filters users with distinct cities

C It sorts the users by city

D It returns only one user from the city

💡 Hint

Think about what 'distinct' means in database queries.

'Distinct' ensures the query returns unique results without duplicates.

❓ state_output

expert

What is the size of the result list after calling this method?

Given a User entity with fields id, name, age and a repository method:
List findByAgeBetween(int start, int end);
Assume the database has users with ages: 20, 25, 30, 35, 40.
What is the size of the list returned by findByAgeBetween(25, 35)?

A 2

B 5

C 4

D 3

💡 Hint

The 'Between' keyword includes both start and end values.

Ages 25, 30, and 35 are included, so the list size is 3.

Practice

1. What does a Spring Data JPA method named findByLastName do?

easy

A. Counts records where the lastName matches the given value

B. Deletes records where the lastName matches the given value

C. Checks if any record exists with the given lastName

D. Finds all records where the lastName matches the given value

Solution

1. Step 1: Understand the method prefix

   The prefix findBy in Spring Data JPA means it will search and return matching records.

2. Step 2: Analyze the property name

   The method uses LastName as the property to filter by, so it finds records with that lastName.

3. Final Answer:

   Finds all records where the lastName matches the given value -> Option D

4. Quick Check:

   findBy + property = find matching records [OK]

Hint: findBy means search and return matching records [OK]

Common Mistakes:

• Confusing findBy with deleteBy or countBy
• Thinking it returns a boolean instead of records
• Ignoring the property name after findBy

2. Which of the following is the correct syntax for a method that counts users by their age in Spring Data JPA?

easy

A. findCountByAge(int age);

B. countUsersByAge(int age);

C. countByAge(int age);

D. countAgeBy(int age);

Solution

1. Step 1: Identify the correct prefix for counting

   The correct prefix to count records is countBy.

2. Step 2: Check method naming pattern

   The method should be countByAge to count users filtered by age.

3. Final Answer:

   countByAge(int age); -> Option C

4. Quick Check:

   countBy + property = count matching records [OK]

Hint: Use countBy + property to count records [OK]

Common Mistakes:

• Adding extra words like Users in method name
• Using findCountBy which is invalid
• Placing property name after count instead of after By

3. Given the method existsByEmailAndStatus(String email, String status), what will it return if a user with email "[e-mail]" and status "active" exists?

medium

A. A list of users matching the email and status

B. true

C. false

D. The count of users matching the email and status

Solution

1. Step 1: Understand the method prefix

   The prefix existsBy returns a boolean indicating if any record matches the criteria.

2. Step 2: Analyze the condition

   The method checks if a user exists with the given email and status combined with And.

3. Final Answer:

   true -> Option B

4. Quick Check:

   existsBy + conditions returns boolean [OK]

Hint: existsBy returns true if matching record exists [OK]

Common Mistakes:

• Expecting a list instead of boolean
• Confusing existsBy with findBy
• Ignoring the combined conditions with And

4. Identify the error in this Spring Data JPA method declaration: List<User> findByNameOr(int age, String name);

medium

A. The method name is missing the property after 'Or'

B. The method should use 'And' instead of 'Or' for combining conditions

C. The order of parameters does not match the method name conditions

D. The return type should be boolean for 'findBy' methods

Solution

1. Step 1: Analyze the method name structure

   The method name uses 'Or' but does not specify the property after 'Or'. It should be like 'findByNameOrAge'.

2. Step 2: Check parameter order and names

   Parameters should match the properties in the method name order, but the main error is missing property after 'Or'.

3. Final Answer:

   The method name is missing the property after 'Or' -> Option A

4. Quick Check:

   Method names must specify property after 'Or' [OK]

Hint: After 'Or' or 'And', always specify property name [OK]

Common Mistakes:

• Leaving out property name after 'Or' or 'And'
• Mixing parameter order with method name order
• Using wrong return type for findBy methods

5. You want to create a method that finds all orders where the customer's city is "New York" and the order total is greater than 100. Which method name correctly follows Spring Data JPA naming conventions?

hard

A. findByCustomerCityAndOrderTotalGreaterThan(String city, double total);

B. findOrdersByCityAndTotalGreater(String city, double total);

C. findByCityAndOrderTotalGreaterThan(String city, double total);

D. findByCustomerCityAndOrderTotalGreater(String city, double total);

Solution

1. Step 1: Identify the correct property names

   The properties are nested: customer.city and orderTotal. The method name must reflect this exactly.

2. Step 2: Use correct keywords for comparison

   For 'greater than', the keyword is 'GreaterThan' in Spring Data JPA method names.

3. Step 3: Combine conditions with 'And'

   The method name should combine both conditions with 'And' and use full property paths.

4. Final Answer:

   findByCustomerCityAndOrderTotalGreaterThan(String city, double total); -> Option A

5. Quick Check:

   Use full property names + GreaterThan + And [OK]

Hint: Use full property names and 'GreaterThan' for > comparisons [OK]

Common Mistakes:

• Using incomplete property names
• Using 'Greater' instead of 'GreaterThan'
• Omitting 'By' after 'find'