---
title: "Object Relational Mapping"  
description: "ORM is acronym for Object Relational Mapping, it is a programming technique for converting data between relational database and object"  
author: "Anonymous User"  
published: 2015-10-20  
updated: 2019-11-27  
canonical: https://www.mindstick.com/articles/11881/object-relational-mapping  
category: "java"  
tags: ["database", "java", "orm", "hibernate"]  
reading_time: 4 minutes  

---

# Object Relational Mapping

When we are working with an object –oriented systems, chances are that there may be a mismatch of object model and the relational database.

Since RDBMS represents data in a tabular format whereas object oriented languages like Java, C++, C# represents it as an interconnected graph of objects.

For instance consider the case of Person class here, it consist of private properties, constructors and public methods.

```
public class Person {      private int id;      private String name;      private String address;      private int age;      public Person(int id, String name, String address,int age){            this.id = id;            this.name = name;            this.address = address;            this.age = age;      }      public int getId() {            return id;      }
      public String getName() {            return name;
      }
      public String getAddress() {            return address;
      }
      public int getAge() {            return age;
      }
} 
```

Now this above object need to be stored and retrieved into a RDBMS table

```
create table PERSON (
   id INT NOT NULL auto_increment,   name VARCHAR(20) default NULL,   address  VARCHAR(20) default NULL,   age     INT  default NULL,   PRIMARY KEY (id)
);
```

**1.** If we analyze this model carefully, there is one problem. What if we need to modify the design of our database after having developed few pages or our application?

**2.** Also, loading and storing objects in a relational database exposes us to five other mismatch problems:

**a.** Inheritance: RDBMSs don’t define anything similar to inheritance which is a natural paradigm in OOPS languages.

**b**. Granularity: Sometimes we will have an object model which has more classes than the number of corresponding tables in the database.

**c.** Navigation: The ways we access objects in java and in a RDBMS are fundamentally different.

**d**. Identity: A RDBMS defines exactly one notion of ‘sameness’, the primary key. But java, defines both object identity (x == y) and object equality (equals(y)).

**e.** Associations: Object-oriented languages represent associations using object references where as a RDBMS represent an association as a foreign key.

For all handling all these impedance mismatches we use Object Relational Mapping (ORM). It take care of all the differences between an object and an RDMS.

##### ORM Definition:

#####

ORM is acronym for Object Relational Mapping, it is a programming technique for converting data between relational database and object oriented programming languages like Java, C++, and C#.

##### ORM Benefits:

- ORM make us get rid of database implementations. There is no need to handle DB logics.

- It hides details of SQL queries from Object Oriented logic.

- Let business code access objects rather than DB tables.

- It is uses JDBC as a base layer.

- Entities are based on business concepts rather than database structure.

- It is equipped with features like Transaction management and automatic key generation.

- Increase the pace of application development.

##### \

##### ORM components:

##### ORM consists of four important component entities:

1. An API to perform basic CRUD operations on objects of persistent classes.
2. A language or API to specify queries that refer to classes and properties of classes.
3. A configurable facility for specifying mapping Meta data.
4. A technique to interact with transactional objects to perform dirty checking, lazy association fetching, and other optimization functions.

##### Java ORM Frameworks:

A persistence firework is an ORM service that stores and retrieves objects into a relational database.\

- Enterprise JavaBeans Entity Beans
- Java Data Objects
- Castor
- TopLink
- Spring DAO
- Hibernate

---

Original Source: https://www.mindstick.com/articles/11881/object-relational-mapping

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