The most frequent type of relationship is a many-to-one association, in which one Object can be connected with numerous objects. A single address object, for example, can be linked to many employee objects.
Consider the following scenario: We need to keep track of our employees in the EMPLOYEE table, which will have the following structure:
build a table called EMPLOYEE (
auto increment id INT NOT NULL,
default NULL, first name VARCHAR(20),
VARCHAR(20) default NULL, last name
INT default on salary NULL,
address INT NOT NULL,,,,,,,,,,,,,,,
Furthermore, because several employees may have the same address, this link might be portrayed as a many-to-one relationship. We'll keep track of address information in a separate table with the following structure:
make a table called ADDRESS (
auto increment id INT NOT NULL,
VARCHAR(40) default NULL, street name
VARCHAR(40) default NULL, city name
VARCHAR(40) default NULL, state name
VARCHAR(10) default NULL, zipcode
THE MAIN KEY (id)
);
A many-to-one connection occurs when one entity includes values that refer to a different entity (a column or collection of columns) with unique values. These many-to-one links are frequently enforced via foreign key/primary key relationships in relational databases. The linkages are generally between fact and dimension tables and between levels in a hierarchy.
A many-to-one connection arises in relational database systems when numerous child entries in one table can refer to a single record in the parent table. This example shows you how to use Hibernate to map a many to one relationship.
To map entities having many to one connections in Hibernate, we must first describe their relationship. The parent class dependence (parent class reference variable) must be defined in the child class.
Only the child class should do the actions (Save, Update, and Delete).The appropriate parent class will be automatically affected using multiple map configurations in the hibernate map file.
Hibernate one to many mapping is a relationship between two entities in which the first entity can have numerous instances of the second entity. Still, the second entity can only have one example of the first Object, and it's a one-to-one correspondence.
An employee, for example, can register several bank accounts in any firm, but each bank account will be connected with just one employee. We will learn how to build such a mapping in the database using hibernate in these hibernate to many mapping annotations in the following topics.
