Using MySQL, why doesn't Hibernate/JPA create foreign key constraints for me?

Question

Documenting this here because I just wasted an hour trying to figure this out.

I have an entity Foo with:

@ManyToOne(optional = false)
@JoinColumn(name = "barId")
private Bar bar;

Why does Hibernate not create a foreign key constraint on foo.bar -> bar.id ?

Answer 1

As suggested here Hibernate: Create Mysql InnoDB tables instead of MyISAM you can also change Hibernate dialect to use

org.hibernate.dialect.MySQL5InnoDBDialect

which is less invasive.

Just wanted to add this as an alternative solution.

Answer 2

It's because MySQL does not support foreign key constraints on tables created with ENGINE=MyISAM. You need to create (both!) tables with ENGINE=InnoDB. You can do so by tweaking my.cnf, and adding a default, or by using a special variable in your JDBC URL:

jdbc:mysql://localhost/dbname?characterEncoding=utf8&sessionVariables=storage_engine=InnoDB

Answer 3

With SpringBoot you can set application.properties to:

spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5InnoDBDialect   

and it should work fine.