Custom query methods by naming convention in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom query method by naming convention in Spring Boot?

It is a method in a Spring Data repository interface whose name follows a pattern that Spring Data understands to create a database query automatically without writing SQL.

intermediate

How does Spring Boot know what query to run from a method name?

Spring Data parses the method name to identify keywords like findBy, countBy, and conditions like And, Or, GreaterThan, then builds the query based on the entity's fields.

beginner

Example: What does the method name findByLastNameAndAgeGreaterThan mean?

It means find all records where the lastName field matches the given value AND the age field is greater than the given number.

intermediate

Can you use custom query methods for sorting and limiting results?

Yes, by adding keywords like OrderBy and using Pageable parameters, you can sort and limit results using naming conventions.

beginner

What happens if a method name does not follow Spring Boot's naming conventions?

Spring Data will throw an error or fail to create the query because it cannot understand how to translate the method name into a database query.

Which prefix is used to create a method that returns a list of entities matching a condition?

A updateBy

B deleteBy

C insertBy

D findBy

The prefix 'findBy' tells Spring Data to find and return entities matching the condition.

What does the method name countByStatus do?

A Deletes entities with a given status

B Counts entities with a given status

C Finds entities with a given status

D Updates entities with a given status

'countBy' counts how many entities match the condition.

Which keyword would you use to combine two conditions in a method name?

A And

B Or

C Not

D Between

'And' combines two conditions that both must be true.

How do you specify sorting in a custom query method name?

A Add 'GroupBy' followed by the field name

B Add 'SortBy' followed by the field name

C Add 'OrderBy' followed by the field name

D Add 'FilterBy' followed by the field name

'OrderBy' is used to specify sorting in the method name.

What will happen if you name a method findAllUsers in a Spring Data repository?

A Spring Data will not recognize it as a query method

B It will find all users

C It will delete all users

D It will update all users

The method name does not follow the naming convention for queries, so Spring Data cannot create a query.

Explain how Spring Boot creates database queries from custom method names in repositories.

Think about how the method name tells Spring Boot what to look for in the database.

Describe how you would write a method name to find all records where age is greater than 30 and status is 'active'.

Combine conditions with 'And' and use comparison keywords.

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'