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breadcrumb:
  - Guides
  - ORM
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# Object-Relational Mapping

## Definition

> **Object-relational mapping** (**ORM**, **O/RM**, and **O/R mapping tool**) in computer science is a programming
> technique for converting data between incompatible type systems using 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
> construct their own ORM tools.
>
> In object-oriented programming, data-management tasks act on object-oriented (OO) objects that are almost always
> non-scalar values. For example, an address book entry that represents a single person along with zero or more phone
> numbers and zero or more addresses. This could be modeled in an object-oriented implementation by a "Person object" with
> attributes/fields to hold each data item that the entry comprises: the person's name, a list of phone numbers, and a
> list of addresses. The list of phone numbers would itself contain "PhoneNumber objects" and so on. The address-book
> entry is treated as a single object by the programming language (it can be referenced by a single variable containing a
> pointer to the object, for instance). Various methods can be associated with the object, such as a method to return the
> preferred phone number, the home address, and so on.
>
> However, many popular database products such as SQL database management systems (DBMS) can only store and manipulate
> scalar values such as integers and strings organized within tables. The programmer must either convert the object values
> into groups of simpler values for storage in the database (and convert them back upon retrieval), or only use simple
> scalar values within the program. Object-relational mapping implements the first approach.
>
> The heart of the problem involves translating the logical representation of the objects into an atomized form that is
> capable of being stored in the database while preserving the properties of the objects and their relationships so that
> they can be reloaded as objects when needed. If this storage and retrieval functionality is implemented, the objects are
> said to be persistent.
>
> Source: [Wikipedia](https://en.wikipedia.org/wiki/Object-relational_mapping)

## List

Berlioz purposes some packages:

- [Hector ORM](orm/hector.md)
- [Atlas ORM](orm/atlas.md)