A one-to-one relationship is identical to a many-to-one association, except that the column is specified to be unique. An address object, for example, can be linked to a single employee object.
In a relational database, a one-to-one connection occurs when a parent table record has zero or one child record in the child table. In this tutorial, we'll use XML configuration to build one-to-one mapping in Hibernate (relationship).
In basic words, a One-to-One connection is identical to a Many-to-One relationship with the exception that the column will be set to unique, i.e. two entities are said to be in a One-to-One relationship if one entity has just one occurrence in the other entity. An address object, for example, can be linked to a single employee object. On the other hand, these relationships are infrequently utilised in relational table models, and therefore we won't require this mapping very often.
To define a One to One relationship using hibernate, annotation @OneToOne needs to be placed before the class reference variable declaration or before the getter method of this reference variable.
Now, we must call the setter method for the department reference variable into the OneToOneMapping class bypassing the department class object.