PostgreSQL is an ORDBMS, or an Object-Relational Database Management System. This means that, similar to Object-Oriented programming languages, objects, classes, and inheritance are supported by PostgreSQL.
In addition to having the characteristics of a relational database (in which data is stored in rows and tables in a database), PostgreSQL is capable of storing data as objects in a database.
Object-Oriented Models in a Database
In software development, objects are models that contain data (known as attributes, or properties), and code (known as procedures, or methods)
Objects allow for complex models to be developed in software. For example, you could have a “Cat” object that has the properties of a tail, and whiskers. Objects can be composed from other objects, and inherit the properties of those objects. So, if a Cat object inherits from an Animal object, the Cat will inherit all the properties of an Animal, but will retain all the characteristics that make it uniquely a cat.
Since PostgreSQL is able to store data as objects, developers are able to create complex objects to be stored and later retrieved in a PostgreSQL database.
Built-In PostgreSQL Data Types
PostgreSQL offers built-in data types that are more complex than a relational database like MySQL, including:
Extending Data Types
Because of its support for Object-Oriented characteristics, PostgreSQL makes it possible to extend data types to create custom data types. This allows for a high level of flexibility for developers working with complex data models tasks that need to integrate with a database. These custom types inherit all of the properties of the object that they are based off of.
So, if you create a custom data type based off of two existing, parent data types; the custom data type will have whatever new properties have been added to it by the developer, as well as all of the properties of the two parent data types.
Support for Complex Data Allows for Complex Applications
Since PostgreSQL allows for data models to be created through Object-Oriented properties, deve lopers can create custom data objects which facilitate the development of complex applications, whose behavior can only be modeled through these custom objects.
Table Inheritance
The Object-Oriented nature of PostgreSQL also includes table-inheritance. A child table can inherit columns from a parent table; so that the child table has all the columns that a parent table has, in addition to the new columns that make the child table distinct to itself.
An example of this, from the PostgreSQL documentation, would be a table of CAPITALS that inherits from a table of CITIES:
The Object-Oriented nature of PostgreSQL also includes table-inheritance. A child table can inherit columns from a parent table; so that the child table has all the columns that a parent table has, in addition to the new columns that make the child table distinct to itself.
Soft Deletion
Another feature supported by PostgresSQL is Soft Deletion. Hard Deletion is when rows in a database get deleted using `DELETE FROM table WHERE …`.
Soft Deletion occurs when rows in the database are deleted using `UPDATE table SET deleted_at = now() WHERE …`.
The Soft Deletion feature allows for data to be easily recovered if it gets accidentally deleted by the user; a benefit over Hard Deletion.
