Explain About Mapping Description File

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Mapping description file is the second file which Hibernate uses to configure its functions. This mapping file has an extension *.hbm which instructs mapping between Java class and database tables. The usage of mapping description file rests entirely upon the business entity.

In the context of advanced Java, it seems like you might be referring to Hibernate, a popular Java-based framework for object-relational mapping (ORM). In Hibernate, the mapping description file typically refers to the Hibernate Mapping file (hbm.xml).

Hibernate Mapping files are XML files used to define the mapping between Java objects and database tables. They provide a declarative way to specify how the fields and properties of Java classes are mapped to the columns of database tables. The mapping file contains information about the class-to-table mapping, property-to-column mapping, associations, and other metadata necessary for Hibernate to interact with the database.

Here’s a brief overview of what you might find in a Hibernate mapping description file:

  1. Class-to-Table Mapping:
    • Specifies the mapping between a Java class and a database table.
    • Includes information about the table name, schema, and catalog.
  2. Property-to-Column Mapping:
    • Defines how the fields or properties of a Java class map to the columns of a database table.
    • Specifies the column name, data type, and other attributes.
  3. Primary Key Mapping:
    • Describes how the primary key of a table is mapped to the corresponding field or property in the Java class.
  4. Association Mapping:
    • Deals with relationships between different classes/entities.
    • Defines how to represent associations like one-to-many, many-to-one, and many-to-many in the database.
  5. Inheritance Mapping:
    • If the Java classes use inheritance, the mapping file specifies how the inheritance hierarchy is mapped to the database tables.

An example of a simple Hibernate mapping description file (hbm.xml) might look like this:

xml
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.example.model">
<class name="Person" table="people">
<id name="id" type="int">
<generator class="increment"/>
</id>
<property name="firstName" column="first_name" type="string"/>
<property name="lastName" column="last_name" type="string"/>
</class>
</hibernate-mapping>

In this example, the mapping file describes a simple Person class mapping to a table named “people” with three columns: “id,” “first_name,” and “last_name.”

Please note that the specifics may vary depending on the ORM framework or technology you are using, and the term “mapping description file” may have different meanings in other contexts.