NAME
DBIx::EAV::Manual - Well ... rftm.
WHAT'S EAV?
EAV is a data model where instead of representing each entity using a physical table with columns representing its attributes, everything is stored as rows of the eav tables. Each entity is stored as a row of the 'entities' table, and each of its attributes values are stored as a row of one of the values table. There is one value table for each data type.
For a better explanation of what an Entity-Attribute-Value data model is, check this Wikipedia article. The specific tables used by this implementation are described in "TABLES" in DBIx::EAV::Schema.
EAV USE CASES
When the number of possible attributes is huge
EAV modeling has been used by health and clinical software by decades because the number of possible attributes like tests results and diagnostics are huge and just a few of those attributes are acctualy filled (non-NULL).
When you dont't know your schema in advance
E-commerce solutions use EAV modeling to allow the definition of any kind of product and still be able to do filtering/sorting of results based of product attributes. For example, the entity 'HardDrive' would have atrributes 'capacity' and 'rpm', while entity 'Monitor' would have attributes 'resolution' and 'contrast_ratio'.
To abstract the physical database layer
Many SaaS platforms use EAV modeling to offer database services to its custormers, without exposing the physical database system.
When you need frequent changes to your schema
An open-schema data model can be useful for app prototyping.
DBIx::EAV CONCEPTS
EntityType
An EntityType is the blueprint of an entity. Like a Class in OOP. Each type has a unique name, one or more attributes and zero or more relationships. See DBIx::EAV::EntityType.
Entity
An actual entity record (of some type) that has its own id and attribute values. See DBIx::EAV::Entity.
Attribute
Attributes are analogous to columns in traditional database modeling. Its the actual named properties that describes an entity type. Every attribute has a unique name and a data type. Unlike traditional table columns, adding/removing attributes to an existing entity type is very easy and cheap.
Value
The actual attribute data stored in one of the value tables. There is one value table for each data type. See "data_types", DBIx::EAV::Schema.
ResultSet
Concept borrowed from DBIx::Class, a ResultSet represents a query used for fetching a set of entities of a type, as well as other CRUD operations on multiple entities.
Relationships
Physical Schema
This is the actual database tables used by the EAV system. Its represented by DBIx::EAV::Schema.
EAV Schema
Its the total set of Entity Types registered on the system, which form the actual application business model. See "register_types".
Cursor
A Cursor is used internally by the ResultSet to prepare, execute and traverse through SELECT queries.
RELATIONSHIPS
has_one
has_many
many_to_many
LICENSE
Copyright (C) Carlos Fernando Avila Gratz.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
AUTHOR
Carlos Fernando Avila Gratz <cafe@kreato.com.br>