# Abstract base classes¶

Abstract base classes are useful when you want to put some common information into a number of other models. You create an Abstract base class by simply creating a normal php abstract base class.

This model will then not be used to create any database table.

Instead, when it is used as a base class for other models, its fields will be added to those of the child class.

Any fields defined in the Abstract that are again defined in the Child class will be over written by those in the child class.:

use Eddmash\PowerOrm\Model\Model;

abstract class CommonInfo extends Model
{
public function unboundFields()
{
return [
'name' => Model::CharField(['maxLength' => 100]),
'age' => Model::IntegerField()
];
}
}

class Student extends CommonInfo
{
public function unboundFields()
{
return [
'home_group' => Model::CharField(['maxLength' => 5])
];
}
}


The Student model will have three fields: name, age and home_group.

The CommonInfo model cannot be used as a normal model, since it is an abstract base class. It does not generate a database table, and cannot be instantiated or saved directly.

For many uses, this type of model inheritance will be exactly what you want.

It provides a way to factor out common information at the php level, while still only creating one database table per child model at the database level.

## Meta inheritance¶

When inheriting, Some attributes will need to be overridden in child classes, since it doesn’t make sense to set them in the base class.

For example, setting dbtable would mean that all the child classes (the ones that don’t specify dbtable explicitly) would use the same database table,which is almost certainly not what you want.