\"Hibernate One-To-Many Mapping Error: \\\"Could not Determine Type for: java.util.List\\\" - Why and How to Fix It?\"

Hibernate One-To-Many Mapping Error: "Could not Determine Type for: java.util.List"

In Hibernate, handling One-To-Many relationships requires careful mapping configurations. This error typically occurs when the mapping annotations are incorrectly placed or configured.

Analyzing the provided code, we encounter the below error:

org.hibernate.MappingException: Could not determine type for: java.util.List, at table: College, for columns: [org.hibernate.mapping.Column(students)]

This error indicates that Hibernate is unable to determine the type of the students property in the College class. According to the provided mapping, the students property is annotated with @OneToMany and is of type List, but the annotation is placed incorrectly.

Correct Annotation Placement

In field access strategy, which is determined by the @Id annotation, JPA annotations should be placed right above each field instead of getter properties. In this case, the correct annotation placement for the students property is:

@OneToMany(targetEntity=Student.class, mappedBy="college", fetch=FetchType.EAGER)
private List<Student> students;

Modified College Class

With the annotation placement corrected, the modified College class looks like this:

@Entity
public class College {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int collegeId;
private String collegeName;

@OneToMany(targetEntity=Student.class, mappedBy="college", fetch=FetchType.EAGER)
private List<Student> students; // Annotation is now placed above the field

// Other getters and setters omitted
}

Conclusion

By correctly placing the @OneToMany annotation above the students field, Hibernate can now properly determine the type of the property and map the One-To-Many relationship between College and Student. This adjustment resolves the "Could not determine type for: java.util.List" error.

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