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=encoding utf-8

=head1 NAME

DBIx::EAV::Manual - Users Manual

=head1 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 L<Wikipedia article|https://en.wikipedia.org/wiki/Entity%E2%80%93attribute%E2%80%93value_model>.
The specific tables used by this implementation are described in
L<DBIx::EAV::Schema/TABLES>.

=head1 EAV USE CASES

=head2 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).

=head2 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'.

=head2 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.

=head2 When you need frequent changes to your schema

An open-schema data model can be useful for app prototyping.

=head1 DBIx::EAV CONCEPTS

=head2 EntityType

An L<EntityType|DBIx::EAV::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 L<DBIx::EAV::EntityType>.

=head2 Entity

An actual entity record (of some type) that has its own id and attribute values.
See L<DBIx::EAV::Entity>.

=head2 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.

=head2 Value

The actual attribute data stored in one of the value tables. There is one value
table for each data type.
See L</data_types>, L<DBIx::EAV::Schema>.

=head2 ResultSet

Concept borrowed from L<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.

=head2 Relationships

=head2 Physical Schema

This is the actual database tables used by the EAV system. Its represented by
L<DBIx::EAV::Schema>.

=head2 EAV Schema

Its the total set of Entity Types registered on the system, which form the
actual application business model.
See L</register_types>.

=head2 Cursor

A Cursor is used internally by the ResultSet to prepare, execute and traverse
through SELECT queries.


=head1 RELATIONSHIPS

=head2 has_one

=head2 has_many

=head2 many_to_many

=head1 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.

=head1 AUTHOR

Carlos Fernando Avila Gratz E<lt>cafe@kreato.com.brE<gt>

=cut