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Internals / Bolt Storage Overview

Note: You are currently reading the documentation for Bolt 3.7. Looking for the documentation for Bolt 5.2 instead?

As of version 3.0 a major refactor of the storage system has been started and during the 3.0 and 4.0 version releases we are committed to maintaining backwards compatibility wherever possible and so at points in this page we will refer to 'Legacy Storage' in reference to pre 3.0 storage classes. All of the new storage classes can be found in src/Storage/ and predominantly the legacy functionality can be found in two classes, src/Legacy/Storage.php and src/Legacy/Content.

Philosophy Behind the Refactor

The overall goal of the refactor is to break up the system into many smaller well-defined parts and, building on the service-definition approach of Silex, exposing these smaller components to the application as a separate service.

This gives both application developers and extension developers a lot more ability to build on Bolt and from an internals point of view it means smaller components can be iterated on separately which can vastly reduce the time needed to bring new features to release.

A secondary goal is also to align Bolt more closely with the Symfony/Doctrine syntaxes so that developers have a reduced cognitive load when understanding how to use Bolt. Whilst Bolt is not suited to be built on top of Doctrine, wherever possible we try to use the same approaches and divisions of responsibility.

The Field is King

Perhaps the overarching philosophy of the new storage system is that the field, and its companion 'field-type' is the primary unit of functionality within Bolt. A contenttype and its records are now just loose wrappers that hold together collections of fields, field-types are now responsible for defining how they are loaded and saved to the database, how they are queried for and how they are presented to the frontend.

A Brief Overview of Storage Components

A good way to understand the different components is to look at the sub-directory structure inside the src/Storage folder. Here's a quick overview of each one which we will then go into more depth further down the page.


Collections are simply groups of other entities. In Bolt the primary example of these are relations and taxonomies which show up as iterable groups of other items. Bolt comes with the Doctrine Collections library as a dependency and Bolt's collections normally build on top of an ArrayCollection of some kind.


This component takes care of handling the HTTP requests from the Bolt backend. When a user presses view, save, create or delete then these classes translate those requests into operations on the DB Storage layer.


This section contains anything related to the low-level database interaction. It also includes the functionality that keeps the database structure up to date.


An entity is a PHP representation of a database row, if you look inside the folder you'll see that we have one entity class for each fixed table in the Bolt schema along with a fallback one called Entity\Content which maps to the dynamic tables that are created for each new contenttype the user adds to contenttypes.yml. An entity should always be a plain PHP object with no interfaces or inheritance that just responds to getX and setX methods.


The majority of functionality for Fields can be found in the classes within src/Field/Type simply put a definition in contenttypes.yml that looks like:

    type: slug

will mean that a field type will be used to handle the functionality, in this case we'd look at src/Field/Type/SlugType although the precise mappings between contenttypes.yml type names and PHP classes are defined in the StorageServiceProvider. Of course this means that whilst Bolt has built in handlers for default types, anyone can add new ones or swap out Bolt's default behaviour by mapping to a different class.


Mapping supplies information about data structures between the PHP objects and the underlying data layer. Bolt primarily uses a combination of introspection (looking at the existing db schema) and configuration (mostly set in contenttypes.yml) to determine what this is.

Having this information available allows the PHP objects to find out what the underlying data structure is, and also allows mapping between the two, for instance an object of the class Bolt\Entity\Users will be mapped to the table bolt_users and the attribute $user->lastSeen or more precisely $user->getLastSeen() will map to bolt_users.lastseen.


This folder is responsible for file-based database migration which is only currently exposed via the experimental nut commands database:import and database:export.


This component handles everything to do with higher-level fetching of content which in Bolt is often used via the Twig setcontent tag. The corresponding PHP service is accessed via $app['query']->getContent().

It's job is to take simple text-based queries like {% setcontent somecontent = '(pages,entries)' where {id: '!10', categories: 'news||about' } orderby '-datepublish' %} then parse and turn into platform-specific SQL queries.


A repository is a PHP-Object equivalent of a database table. Within the src/Repository folder you'll see a separate repository class for each Bolt table. Via a repository you can ask for a collection of entities (db rows) and also save and delete entities.

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