Spring Data JPA repository methods don't recognize property names with underscores

Question

I have underscores in the entity property names, and when Spring tries to create the JPA repository implementation, it results in an exception trying to resolve the name of the property.

Entity:

@Entity
public class Student {
      @Id
      private String s_id;
      private String s_name;
      ...
}

Repository:

 @Repository
 @Transactional
 public interface StudentRepository extends CrudRepository<Student, String> {

       List<Student> findByS__name(String name);

}

Exception:

org.springframework.data.mapping.PropertyReferenceException: 
No property s found for type Student

It is said here http://docs.spring.io/spring-data/jpa/docs/current/reference/html/

If your property names contain underscores (e.g. first_name) you can escape the underscore in the method name with a second underscore. For a first_name property the query method would have to be named findByFirst__name(…).

I just did as document said, but I still got the exception. I dont want write @Query by myself, and I need underscore in my property name, how to fix this problem?

I use Spring data jpa 1.8.0.RELEASE + hibernate 4.3.9.Final

Answer 1

Avoid using underscores in the entity property names if you have control over the property naming. This will resolve your repository woes, and will result in a cleaner code-base. Developers dealing with the code after you will thank you.

Note, it's not just my opinion: Spring specifically discourages using underscores.

As we treat underscore as a reserved character we strongly advise to follow standard Java naming conventions (i.e. not using underscores in property names but camel case instead).

this JIRA issue shows why the documentation was updated with this reccomendation, and the part describing the double underscore option were removed.

I suspect your root problem is that Spring/Hibernate is not mapping camel case property names to the snake case names you have for your columns in the database. What you really need is for your property name to be interpreted in the SQL that hiberate generates as S_NAME.

Is that why underscores in your property name are "required"? If so, there are a few solutions:

Option 1: @Column annotation

To get JPA/Hibernate to map to the correct column names you can tell it the names explicitly. Use the annotation @Column(name="...") to tell it what column names to use in SQL. Then the field names are not constrained by the column names.

@Entity
public class Student {
     @Id
     @Column(name="s_id")
     private String sId;
     @Column(name="s_name")
     private String sName;

     //...getters and setters...
}

Option 2: Improved Naming Strategy
Or if your application has a large number of entities, rather than adding @Column to every property, change the default naming strategy in your configuration file to the hibernate improved naming strategy.

<prop key="hibernate.ejb.naming_strategy">org.hibernate.cfg.ImprovedNamingStrategy</prop>

This naming strategy will convert camelCase to SNAKE_CASE. Then your class could look as simple as this:

@Entity
public class Student {
     @Id
     private String sId;
     private String sName;

     //...getters and setters...
}

Using either of those options, when it creates the SQL it will resolve the column names to:

 S_ID
 S_NAME

Note: If you are using, or can use Spring Boot, the auto-configuration default will use SpringNamingStrategy, which is a slightly modified version of the hibernate improved strategy. You won't have to do anything to get this improved naming strategy.

The finish line:

Using camel case in your property names you can write your repository method name using camel case, and you can stop trying to wrangle the double underscore:

@Repository
@Transactional
public interface StudentRepository extends CrudRepository<Student, String> {  
       List<Student> findBySName(String name);   
}

Answer 2

Writing double underscore i.e. writing findByS__Name() for property name s_name just does not work. I have tried and tested it. Go by the above answer and change the name of existing instance variables in your entity class. Just dont change getters and setters as they might be used in the existing code.