Table Per Concrete

Benefits and Drawbacks 

The benefits and drawbacks of Table per Concrete Class Mapping are listed below.

Benefits

• This inheritance mapping approach is very easy to use.
   
• It makes the program very clear and easy to understand.

Drawbacks

• A parent class's data is dispersed throughout several subclass tables representing concrete classes.
   
• A significant number of tables reflect changes a/c to the parent class.

Example

Assume for a moment that you want to convert the entire hierarchy shown below into a meaningful relational database schema. Both the PartTime_Employee and FullTime_Employee classes are subclasses of the Employee class.

The DB schema illustrated in the following diagram is the result of using the pattern just described:

that(one on top) turns to this(image below):

This hierarchy's corresponding mapping file should be:

<?xml version='1.0' encoding='UTF-8'?>  
<!DOCTYPE hibernate-mapping PUBLIC 
   "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
   "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">


<hibernate-mapping>
    <class name="Employee" table="EMPLOYEE">
        <id name="id" column="id">
            <generator class="increment"></generator>
        </id>


        <property name="name"  column="name"></property>


        <union-subclass name="PartTime_Employee"
            table="REGULAR EMPLOYEE">
            <property name="salary" column="salary"></property>
            <property name="bonus" column="bonus"></property>
        </union-subclass>


        <union-subclass name="FullTime_Employee"
            table="CONTRACT EMPLOYEE">
            <property name="payPerHour" column="pay_per_hour"></property>
            <property name="contractDuration" column="contract_duration"></property>
        </union-subclass>
    </class>
</hibernate-mapping>

If the DB has relationships with multi-levels of inheritance, you must reflect them in the ORM file by recursively nesting each definition.

Frequently Asked Questions

What is the Table per concrete class in hibernate?

Hibernate maintains each derived class object of the hierarchy in a different database table using the Table per Concrete Class technique. A parent class's data is dispersed throughout several subclass tables, which stand in for actual courses.

When a Table per concrete class is used, will three tables be present?

I am using an XML file, one Table per concrete class. Three tables with no relationships to one another will be present in the Table Per Concrete class database. The Table with Table per concrete class technique may be mapped in two different ways.

What is the Table per subclass in hibernate?

A main key column that connects two different tables by acting as a foreign key is specified by this annotation. In the JOINED mapping approach, it is used to link the primary Table of an entity subclass to the primary Table of its superclass.

What is the Table per concrete class mapping?

In the inheritance hierarchy, for each concrete class, a table is established in the "Table Per Concrete Class" approach, containing all of the attributes of the course and its superclasses. This tactic is optional in certain ORM technologies (like JPA), and querying root or branch classes might be time-consuming and ineffective.

What is dirty checking in hibernate?

Hibernate tracks all permanent objects. It is aware of which items have undergone modification after a work unit. The update statement is then executed on all updated things. In hibernation, this procedure of keeping track of and updating only modified items is known as automated dirty checking.

Conclusion

So that's the end of the article. Table Per Concrete

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