How to Resolve Hibernate @JoinFormula Error: Casting Issue Between Formula and Column

What causes the error 'org.hibernate.mapping.Formula cannot be cast to org.hibernate.mapping.Column' when using @JoinFormula in Hibernate?

The error message 'org.hibernate.mapping.Formula cannot be cast to org.hibernate.mapping.Column' typically occurs when there is a mismatch in the expected types in Hibernate's ORM mapping. This commonly happens when you attempt to use the @JoinFormula annotation improperly or when the underlying mapping logic has conflicts.

@Entity
public class Employee {
    @Id
    private Long id;

    @JoinFormula("(SELECT d.name FROM Department d WHERE d.id = department_id)"
    private String departmentName;
}

Causes

• Using @JoinFormula with an incorrect SQL expression.
• Misconfiguring the entity relationships leading to type mismatches.
• Not aligning the expected and actual types in entity mappings.

Solutions

• Ensure that the SQL expression used in @JoinFormula is returning the correct data type.
• Check the entity relationship configurations to ensure they are set up correctly for expected types.
• Review the Hibernate entity mappings and adjust them to prevent conflicts.

Mistake: Using an invalid SQL expression in @JoinFormula.

Solution: Verify that the SQL is syntactically correct and logically returns a valid type.

Mistake: Incorrectly assuming the mapped type from @JoinFormula will match Column types.

Solution: Confirm that the type returned by the @JoinFormula reflects the field it is assigned to.