Confusion NotNull vs Column nullable false with JPA and Hibernate

Question

When they appear on a field getter of an  Entity  what is the difference between them   I persist the Entity through Hibernate   What framework and or specification each one of them belongs to   NotNull is located within javax validation constraints  In the javax validation constraints NotNull javadoc it says     The annotated element must not be null   but it does not speak of the element s representation in the database  so why would I add the constraint nullable false to the column

User · Accepted Answer

NotNull is a JSR 303 Bean Validation annotation  It has nothing to do with database constraints itself  As Hibernate is the reference implementation of JSR 303  however  it intelligently picks up on these constraints and translates them into database constraints for you  so you get two for the price of one   Column nullable   false  is the JPA way of declaring a column to be not-null  I e  the former is intended for validation and the latter for indicating database schema details  You re just getting some extra  and welcome   help from Hibernate on the validation annotations

User · Answer

The most recent versions of hibernate JPA provider applies the bean validation constraints  JSR 303  like  NotNull to DDL by default  thanks to hibernate validator apply to ddl property defaults to true   But there is no guarantee that other JPA providers do or even have the ability to do that   You should use bean validation annotations like  NotNull to ensure  that bean properties are set to a none-null value  when validating java beans in the JVM  this has nothing to do with database constraints  but in most situations should correspond to them    You should additionally use the JPA annotation like  Column nullable   false  to give the jpa provider hints to generate the right DDL for creating table  columns with the database constraints you want  If you can or want to rely on a JPA provider like Hibernate  which applies the bean validation constraints to DDL by default  then you can omit them

User · Answer

The JPA  Column Annotation The nullable attribute of the  Column annotation has two purposes   it s used by the schema generation tool it s used by Hibernate during flushing the Persistence Context  Schema Generation Tool The HBM2DDL schema generation tool translates the  Column nullable   false  entity attribute to a NOT NULL constraint for the associated table column when generating the CREATE TABLE statement   As I explained in the Hibernate User Guide   it s better to use a tool like Flyway instead of relying on the HBM2DDL mechanism for generating the database schema   Persistence Context Flush When flushing the Persistence Context  Hibernate ORM also uses the  Column nullable   false  entity attribute  new Nullability  session   checkNullability  values  persister  true     If the validation fails  Hibernate will throw a PropertyValueException  and prevents the INSERT or UPDATE statement to be executed needesly  if    nullability i   amp  amp  value    null           check basic level one nullablilty     throw new PropertyValueException               quot not-null property references a null or transient value quot               persister getEntityName                persister getPropertyNames   i                    The Bean Validation  NotNull Annotation The  NotNull annotation is defined by Bean Validation and  just like Hibernate ORM is the most popular JPA implementation  the most popular Bean Validation implementation is the Hibernate Validator framework  When using Hibernate Validator along with Hibernate ORM  Hibernate Validator will throw a ConstraintViolation when validating the entity

User · Answer

Interesting to note  all sources emphasize that  Column nullable false  is used only for DDL generation    However  even if there is no  NotNull annotation  and hibernate check nullability option is set to true  Hibernate will perform validation of entities to be persisted    It will throw PropertyValueException saying that  not-null property references a null or transient value   if nullable false attributes do not have values  even if such restrictions are not implemented in the database layer    More information about hibernate check nullability option is available here  http   docs jboss org hibernate orm 5 0 userguide html single Hibernate User Guide html configurations-mapping

[java] Confusion: @NotNull vs. @Column(nullable = false) with JPA and Hibernate

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