JPARepository findAllByUsername Return Null but Data Exist

As a developer, we’ve all been there - pouring over our code, trying to figure out why a method that should be returning data is instead spitting out null. In this case, we’re looking at a particularly frustrating issue with JPA’s findAllByUsername method in Spring Boot.

Background: JPA and Repositories

For those unfamiliar with JPA (Java Persistence API), it’s a standard Java library for accessing database resources in an application. When using Spring Boot, repositories are used to interact with the database - they encapsulate the CRUD (Create, Read, Update, Delete) operations that we perform on our data.

In this case, we have a CustomerRepo interface that extends JpaRepository, which provides us with the basic CRUD functionality for our Customer entity. We’ve also defined a custom query method in CustomerRepo using the @Query annotation:

@Query(
    value = "SELECT * FROM Customer c WHERE username = ':username' ORDER BY username ASC LIMIT 1",
    nativeQuery = true
)
public Customer findAllByUsername(@Param("username") String username);

This query is supposed to return us a single Customer instance with the matching username. However, when we call repo.findAllByUsername(usernameToFind), it’s returning null.

The Issue

The problem here is that JPA’s native queries can be tricky to get right, especially when using bind parameters. In our custom query method, we’ve used a single colon (:) followed by the username parameter name - this is how Spring Boot expects us to pass bind parameters in native queries.

However, in our findAllByUsername method, we’re wrapping the username parameter inside quotes:

value = "SELECT * FROM Customer c WHERE username = ':username' ORDER BY username ASC LIMIT 1",

This isn’t actually binding the value of the usernameToFind variable to the :username parameter - instead, it’s treating the string literal 'username' as the actual SQL identifier.

The Fix

So what’s going on here? Well, when we pass a bind parameter in a native query, we need to remove any quotes from its name. In this case, we should change our custom query method to use an underscore (_) instead of a colon:

@Query(
    value = "SELECT * FROM Customer c WHERE username = '_username' ORDER BY username ASC LIMIT 1",
    nativeQuery = true
)
public Customer findAllByUsername(@Param("_username") String username);

By doing this, we’re telling JPA to bind the usernameToFind variable directly to the _username parameter in our SQL query.

Why It Matters

You might be wondering why it’s such a big deal - after all, if we just use an underscore instead of a colon, doesn’t that solve the problem? Not quite. The issue here is more about how Spring Boot interprets bind parameters in native queries than it is about the actual SQL syntax.

When using @Query, Spring Boot can automatically generate an equivalent Java method signature for us - this is called “query method name generation”. In our case, when we use a colon (:) followed by a parameter name, Spring Boot expects us to pass that value as a string literal. By wrapping it in quotes, we’re effectively telling Spring Boot to expect the parameter value to be a string.

However, in JPA’s native query language (which is based on SQL), bind parameters are not surrounded by quotes. They’re simply the colon (:) followed by the parameter name - no quotes required.

So while using an underscore (_) instead of a colon does solve our immediate problem, it’s also worth understanding the underlying mechanics of how Spring Boot and JPA handle bind parameters in native queries.

Conclusion

When working with JPA repositories and native queries, it’s essential to understand how bind parameters work - especially when using @Query methods. By following best practices for naming your bind parameters and removing quotes from their names, we can avoid frustrating issues like the one we’ve encountered here.

Example Use Cases

Here are a few more examples of custom query methods that might be useful in your own applications:

// Finding customers by country
@Query(
    value = "SELECT * FROM Customer c WHERE country = :country ORDER BY username ASC LIMIT 1",
    nativeQuery = true
)
public Customer findAllByUsernameCountry(@Param("country") String country);

// Finding customers by city
@Query(
    value = "SELECT * FROM Customer c WHERE city = :city ORDER BY username ASC LIMIT 1",
    nativeQuery = true
)
public Customer findAllByUsernameCity(@Param("city") String city);

By defining custom query methods like these, you can encapsulate your database access logic in a more convenient and readable way.

Step-by-Step Solution

To fix the issue with findAllByUsername returning null, follow these steps:

1. Check your custom query method for bind parameters - make sure that any colon (:) followed by a parameter name is not surrounded by quotes.
2. Update your custom query method to use an underscore (_) instead of a colon when binding its parameter values.

@Query(
    value = "SELECT * FROM Customer c WHERE username = '_username' ORDER BY username ASC LIMIT 1",
    nativeQuery = true
)
public Customer findAllByUsername(@Param("_username") String username);

By following these steps and best practices, you can avoid frustrating issues with JPA repositories and native queries.

Last modified on 2024-03-04