Note: These are  extracted notes

Modern software development has been more automated by tools or concepts. This enables developer to pay attention to complexity that needs only human brains to handle. ORM is one of them. It automates database transactions, queries and thus reduces coding substantially. Several generic queries are generated implicitly by ORM tools and complex queries and their code also to the great extent are easily developed. ORM reduces development time and efforts.

Object-relational mapping (ORM) is a technology that uses  a metadata descriptor.

It connects application  to a relational database. The similarity between database and object in OOPS is both have data structure that remains same for all instances (rows). So class written any Object oriented language can be mapped to any table in relational database. Object code is written in object-oriented programming (OOP) languages such as Java or C#. ORM converts data between type systems that are unable to coexist within relational databases and OOP languages.

Object-relational mapping (ORM, O/RM, and O/R mapping) in computer software is a programming technique for converting data between incompatible type systems in object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language. There are both free and commercial packages available that perform object-relational mapping, although some programmers opt to create their own ORM tools.

ORM resolves the object code and relational database mismatch with three approaches: bottom up, top-down and meet in the middle. Each approach has its share of benefits and drawbacks. When selecting the best software solution, developers must fully understand the environment and design requirements. 
In addition to the data access technique, ORM's benefits also include:

• Simplified development because it automates object-to-table and table-to-object conversion, resulting in lower development and maintenance costs
• Less code compared to embedded SQL and handwritten stored procedures
• Transparent object caching in the application tier, improving system performance
• An optimized solution making an application faster and easier to maintain
• ORM’s emergence in multiple application development has created disagreement among experts. Key concerns are that ORM does not perform well and that stored procedures might be a better solution. In addition, ORM dependence may result in poorly-designed databases in certain circumstances.

Object Relational Mapping: Frameworks and Advantages

ORM (Object Relational Mapping) wraps your tables or stored procedures in classes in your programming language, so that instead of writing SQL statements to interact with your database, you use methods and properties of objects.

There are a lot of frameworks available for implementing ORM (Object Relational Mapping) in different programming languages.

Based on abstraction, ORM (Object Relational Mapping) manages the mapping details between a set of objects and underlying relational databases, XML repositories or other data sources and sinks, while simultaneously hiding the often changing details of related interfaces from developers and the code they create.

ORM (Object Relational Mapping) hides and encapsulates change in the data source itself, so that when data sources or their APIs change, only ORM needs to change to keep up—not the applications that use ORM to insulate themselves from this kind of effort. This capacity lets developers take advantage of new classes as they become available and also makes it easy to extend ORM-based applications. In many cases, ORM changes can incorporate new technology and capability without requiring changes to the code for related applications.