In Drupal, a Content Type is a pre-defined collection of data types (Fields) which relate to each other by an informational context. In this sense, "context" means "parts that should be considered as a correlated whole."
Content Types are the elements using which the site editors can input (add) original content on a Drupal site, and are the building blocks for structured authoring and content. Content types often work in conjunction with Views, which is one way you can serve up content to your end users; you can control the content types that appear and the order in which they appear. Developers can also customize the authoring experience in the same way.
One way to think of content types is to visualize the contacts on your mobile phone. If you were to duplicate this on a Drupal site you would create a Content Type. You would name your new Content Type (e.g. Contacts), define the information that you wanted to store about each contact (called Fields in Drupal), and then add those Fields (e.g. First name, last name, and mobile phone number, etc.) to that Content Type. You would then use this "Contacts" Content Type to enter the information for each of the contacts you had in your contacts list. You would use a View (as described above) to display your Contacts in a list similar to that which you see on your mobile phone.
The Field UI module provides an administrative user interface (UI) for attaching and managing fields. Fields can be defined at the content-type level for content items and comments, at the vocabulary level for taxonomy terms, and at the site level for user accounts. Other modules may also enable fields to be defined for their data. Field types (text, image, number, etc.) are defined by modules, and collected and managed by the Field module.
There are several decisions you will need to make before defining a field for content, comments, etc.:
- What the field will be called
A field has a label (the name displayed in the user interface) and a machine name (the name used internally). The label can be changed after you create the field, if needed, but the machine name cannot be changed after you have created the field.
- What type of data the field will store
Each field can store one type of data (text, number, file, etc.). When you define a field, you choose a particular field type, which corresponds to the type of data you want to store. The field type cannot be changed after you have created the field.
- How the data will be entered and displayed
Each field type has one or more available "widgets" associated with it; each widget provides a mechanism for data input when you are editing (text box, select list, check boxes, file upload, etc.). Each field type also has one or more display options, which determine how the field is displayed to site visitors. The widget and display options can be changed after you have created the field.
- How many values the field will store?
You can store one value, a specific maximum number of values, or an unlimited number of values in each field. For example, an employee identification number field might store a single number, whereas a phone number field might store multiple phone numbers. This setting can be changed after you have created the field, but if you reduce the maximum number of values after inputting/entering data, you may lose information.
Once you have defined a field, you can reuse it. For example: if you define a custom image field for one content type, and you need to have an image field with the same parameters on another content type, you can add the same field to the second content type, in the Add existing field area of the user interface. You could also add this field to a taxonomy vocabulary, comments, user accounts, etc.
Some settings of a reused field are unique to each use of the field; others are shared across all places you use the field. For example, the label of a text field is unique to each use, while the setting for the number of values is shared.
There are two main reasons for reusing fields. First, reusing fields can save you time over defining new fields. Second, reusing fields also allows you to display, filter, group, and sort content together by field across content types. For example, the contributed Views module allows you to create lists and tables of content. So if you use the same field on multiple content types, you can create a View containing all of those content types together displaying that field, sorted by that field, and/or filtered by that field.
There is one main reason to not reuse a field: different permissions. For example, you may need different user roles to have different levels of access to a field, depending on the content type to which it has been added. This can be difficult if you reuse a field.
- Fields on content items
Fields on content items are defined at the content-type level, on the Manage fields tab of the content type edit page (which you can reach from the Content types page). When you define a field for a content type, each content item of that type will have that field added to it. Some fields, such as the Title and Body, are provided for you when you create a content type, or are provided on content types created by your installation profile.
- Fields on taxonomy terms
Fields on taxonomy terms are defined at the taxonomy vocabulary level, on the Manage fields tab of the vocabulary edit page (which you can reach from the Taxonomy page). When you define a field for a vocabulary, each term in that vocabulary will have that field added to it. For example, you could define an image field for a vocabulary to store an icon with each term.
- Fields on user accounts
Fields on user accounts are defined on a site-wide basis on the Manage fields tab of the Account settings page. When you define a field for user accounts, each user account will have that field added to it. For example, you could add a long text field to allow users to include a biography.
- Fields on comments
Fields on comments are defined at the content-type level, on the Comment fields tab of the content type edit page (which you can reach from the Content types page). When you add a field for comments, each comment on a content item of that type will have that field added to it. For example, you could add a website field to the comments on forum posts, to allow forum commenters to add a link to their website.
If need to remove a field completely one would delete it from all existing content types where it exists.
However, some modules create fields automatically and must be uninstalled to have their fields removed.
A better way to do this is run these two functions:
field_purge_batch(); // note: only run this if you need the field deleted immediately!! otherwise it will just be deleted the next time the cron runs
If you manually delete fields from the database, many things can go wrong. For example, hook_field_delete will not be called and one of your modules might fail and crash the site.
The Fields module was incorporated into Drupal 7. Unlike earlier versions, you do not need to download a separate module to add fields to a content type.
The Content Construction Kit (CCK) in Drupal 6 and lower
Field UI module is the core version of the Drupal 6 CCK module.
Default module: Yes.
Dependencies: Field, Field SQL Storage module or custom storage module.
Related Modules: Field, Field SQL Storage, File, Image, List, Number, Node, Taxonomy, User, Text
API Documentation: Field storage API
Database tables: None.