DataIntegrityViolationException: could not execute statement. When perform save operation for @OneToOne JPA mapping

I am getting "org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement" exception while saving the object into the repository.

Requirement: Plan will have only one Cpricing Object so I have added @OneToOne mapping. Below is the expected table structure.

Plan table
-------------
id | planname

Cpricing table
----------
id | cdata | plan_id(fk)

I have below code changes in Entity classes:

Plan {
    @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "pl")//created one to one mapping between the cPricing
  	private CPricing priceInfo;
}
    
CPricing {       
    @OneToOne(fetch = FetchType.LAZY) //created one to one mapping between the plan
    @JoinColumn(name = "plan_id", nullable = false, unique = true)
    private Plan pl;
}

An Exception is thrown when trying to save Plan object containing CPricing object.

Is the mapping correct ?

Here you put @JoinColumn on CPricing side, so CPricing is the owner of relation you should also set plan for CPricing when you save object in db.
You should do something like Cpricing.setPl(plan) before save.