Creating a Reusable Column Type Annotation for JPA to Set Size and Nullability

Question

I'm working with several tables that have multiple fields sharing common characteristics, such as attributes like length and nullability. For instance, the field Username remains consistent across various tables.

Is it possible to create a custom annotation that automatically sets the size and nullability of these fields? For instance, an annotation like @DescriptionColumn could imply a default length of 255 characters and a non-nullable constraint.

In T-SQL, I would typically create a custom SQL type and apply it to all relevant fields. However, it seems that JPA doesn't directly support custom SQL types. Therefore, I'm exploring the idea of creating a reusable column type annotation to address this requirement.

Has anyone successfully implemented a similar solution or can provide guidance on creating such a custom annotation in JPA? Any insights or examples would be greatly appreciated.

Answer 1

I don't know about custom annotation, but I can offer an example with @CompositeType:

@CompositeType(StringCompositeUserType.class)
String userName;

and type definition:

public class StringCompositeUserType implements CompositeUserType<String> {
    public static class StringMapper {
        @Column(name = "user_name", length = 120, nullable = false)
        String name = "";
    }

    @Override
    public Class<?> embeddable() {
        return StringMapper.java;
    }

    ...
}