Resources

Resources are Zotonic’s main data unit. You may want to familiarise yourself with the Zotonic data model in the User Guide.

Resource properties

Resources are very flexible data units: they can have any property that the developer needs them to have. However, by default, Zotonic’s admin is designed to edit a common set of properties.

Categories

Every resource belongs to a single category.

There is no real distinction between rsc records that are a person, a news item, a video or something else. The only difference is the category of the rsc record, which can easily be changed. Even categories and predicates themselves are represented as rsc records and can, subsequently, have their own page on the web site.

Categories are organized in a hierarchical fashion, and used to organize the resources into meaningful groups. Zotonic has a standard set of categories (see Domain model, but it is very usual to define your own in your own site, resulting in a custom domain model.

In the database, categories are stored in an extra metadata table, category, which defines the hierarchy of categories using the Nested Set model. The tree is strictly hierarchical: Every category has at most a single parent category, and every resource belongs to exactly one category. That a resource can’t belong to more than a single category is done to maintain the datamodel’s simplicity and speed of the searches in the system.

Since in Zotonic, everything is a resource, categories themselves are also resources, namely, resources of the category category. This allows the category to be titled and described, just like other resources. The category table only describes the nested hierarchy of the categories. All other properties of a category are defined by its rsc record.

See also

m_category model reference

Medium

Medium management is described in full in Media. Media metadata is stored in a separate table, called medium, since one media is a medium. When a resource contains a medium, this table holds a record describing it. Amongst others, it stores its mime type, width, height and file size.

Besides the medium table, a medium_deleted table exists. When a medium is deleted then any files referenced by that medium will be added to this table. Zotonic periodically checks this table to delete files that are no longer referenced by any media.

See also

m_media

Blocks

Blocks are a specific feature in a resource. The blocks property of a resource is a list of blocks which can be dynamically added and removed from the resource in the admin edit page. Each module can define their own blocks, which consist of an edit template and a view template.

The survey module uses the blocks feature to allow you to dynamically create a list of questions which a user has to answer.

Todo

Fix blocks documentation

How resources are stored

Each resource on a site is stored in the rsc database table. The resource’s properties are stored in two ways.

  • The core properties are persisted in separate columns. They include id, name, category, modification date, path, publication period. These properties are used for searching, filtering and sorting resources. As they can have unique or foreign key constraints, they help in preserving data sanity.
  • All other properties are serialized together into one binary blob column named props. This includes any custom properties that you set on the resource. These serialized properties cannot be used for finding or sorting data, but only for later retrieval.

Storing properties in a serialized form is a flexible approach. You can save any property on a resource without having to make changes to your database schema.

Imagine you wish to store whether resources are liked by users. Just update the resource and set a custom is_liked property:

m_rsc:update(123, [{is_liked, true}], Context).

is_liked=true will now be stored in the database for resource 123, so you can retrieve it like you would any other property:

?DEBUG(m_rsc:p(123, is_liked, Context)).
%% prints: true

This flexible approach is fine for custom properties that you only want to retrieve and display. However, if you need to find all liked resources, you need to define is_liked as a pivot column (see below).

Pivots

Pivot columns

If you want to search by or order on any custom defined property, you need to define your own database column in a custom pivot.

Note

If you want to find resources on non standard content or texts, then you can change the texts that are pivoted. This can be done by adding specific pivot.tpl templates. See Pivot Templates

The pivot queue

When the version number or modification date of a resource is updated then its id is added to the pivot queue. Zotonic has a pivot process running in the background which looks at this queue and for each queued resource, extract all texts and some other information from the record, filling the pivot columns of the rsc record. The pivot columns are used for searching, they contain amongst others the full text index.

The rsc_pivot_queue table is used to hold the queue of resource ids that are waiting to be pivoted.

The pivot_task_queue holds a second queue for more generic task processing: it holds references to functions which need to be called in the background.

Identities

An rsc record can become a user by adding the user’s credentials to this table. A single user can have multiple kinds of credentials, think of his/her username, openid uri etc. A user isn’t necessarily a person.

See also

m_identity.

Deleted resources

Whenever a resource is deleted, an entry is added to the rsc_gone table. The page and id controllers will serve a 410 Gone when a deleted resource is requested.

See also

m_rsc_gone.