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Definition decoration is a mechanism which allows you to change existing configured items such as apps, dialogs, field types and templates. This page explains the definition decoration concept and provides usage examples. 

Definition decoration concept

Definition decoration is a mechanism that allows you to change the properties and subdefinitions of an existing definition.

It is possible to change definitions such as app descriptors, dialogs, field types, message views, templates, media editors and renderer definitions. Any definition bound to a   Registry  such as TemplateDefinitionRegistry  can be decorated. 

Decorated definitions can originate from any source, including the JCR, YAML files or  even executable code like Blossom. However, decorators themselves can only be defined via YAML for the time being. 

The same definition can be decorated multiple times. When a definition is decorated several times, the decorators are applied in the following order:

  1. Decorators from Magnolia Maven modules* are applied before decorators from light modules.
  2. If there are decorators from different Magnolia Maven modules, they are applied in the dependency order of modules declaring the decorators. **
  3. If there are decorators from different Magnolia light modules, the application order can be unpredictable. You can make it predictable by defining the module loading order of your light modules in the module descriptor.

When two decorators are decorating the same part of a definition, the last decoration applied "wins".

*) A Magnolia Maven module is a Maven packaged module which contains a Magnolia Module descriptor.
**) The Module descriptor defines Module dependencies. If module-a depends on module-b, module-b is loaded before module-a. The module dependencies of all Magnolia Maven modules together define a distinct order. 

Definition decorator file location

Definition decorator files must be stored in the decorations folder of a module. The module can be either a Maven module or a light module (see Module structure). This means that it is possible to decorate definitions using the light development approach. 

The definition decorator resolution mechanism requires decorator file paths correspond to the following pattern: 

<decorating-module-name>/decorations/<target-module-name>/<definition-type>/<def-relative-path>/<def-name>.<path-within-definition>.yaml

  • <decorating-module-name>: Module which declares the definition decorator.
  • decorations: Decorations folder within the decorating module.
  • <target-module-name>: Name of the module that hosts the targeted items to decorate.
  • <definition-type>: Title of the registry containing definitions, such as apps, dialogs, fieldTypes, messageViews, templates, mediaEditors and renderers.
  • <def-relative-path>: Path to the decorated definition within the target module, such as /pages or /components (for templates).
  • <def-name>: Name of the decorated definition, e.g. pages for the name of an app.
  • <path-within-definition>:  Path of the decorated subdefinition, such as subapps.browser.contentConnector.
Magnolia maven moduleLight module
my-maven-module/
└── src
    └── main
        └── resources
            └── my-module
                └── decorations
                    ├── dam-app
                    │   └── apps
                    │       └── assets.subApps.browser.contentConnector.yaml
                    ├── mtk
                    │   └── templates
                    │       └── pages
                    │           ├── basic.cssFiles.yaml
                    │           └── basic.yaml
                    └── pages
                        └── apps
                            └── pages.yaml          
 
 
$magnolia.resources.dir
└── my-module
    └── decorations
        ├── dam-app
        │   └── apps
        │       └── assets.subApps.browser.contentConnector.yaml
        ├── mtk
        │   └── templates
        │       └── pages
        │           ├── basic.cssFiles.yaml
        │           └── basic.yaml
        └── pages
            └── apps
                └── pages.yaml

Definition decorator development in real time

Definition decorator files are loaded in the same way as any other Magnolia resource. See Resources for more. Magnolia's resource change observation mechanism ensures that definition decorators are updated, registered and un-registered in real time, without the necessity of a server restart. (To monitor changes in files coming from the classpath, you must enable the magnolia develop mode, see watching changes of resources).

The effect of a decorator addition, removal or modification is visible on the next decorated definition retrieval attempt. 

Decoration examples

Change the title and the icon of an app

/my-module/decorations/pages/apps/pages.yaml
label: My pages ...
icon: icon-user-me
Result:

Change the root path of the content connector of the assets app

/my-module/decorations/dam-app/apps/dam-app/assets.subApps.browser.contentConnector.yaml
rootPath: /cars/007-cars
Result:

(Screenshot was taken from the definition-app which shows definition items read from the corresponding registry.) 

Add a css file to the mtk page template basic

/my-module/decorations/mtk/templates/pages/basic.yaml
cssFiles:
  chmStyles:
    link: /.resources/my-module/css/chm-style.css
Note: To achieve the same result as with the above file, you also can do this:
/my-module/decorations/mtk/templates/pages/basic.cssFiles.yaml
chmStyles:
  link: /.resources/my-module/css/chm-style.css

Overriding properties and changing subitems

Please note that you can override properties, but you cannot override a subitem completely. You only can add new properties or subitems to an existing subitem. 

To understand the above statement, let's have a look at an example of a (simplified) template definition:

templateScript: /mtk/templates/pages/basic.ftl
dialog: mtk:pages/basic
renderType: freemarker
class: info.magnolia.templating.definition.PageTemplateDefinition
cssFiles:
  normalize:
    link: /.resources/mtk/css/normalize-3.0.3.css
  main:
    link: /.resources/mtk/css/html5boilerplate-main-5.3.0.css
  video:
    link: /.resources/mtk/css/video.css
Here you can completely override the properties templateScriptdialogrenderTypeclass and link, but you cannot completely override the cssFiles subItem. For subitems you can only can add more properties and subItems.

The consequence is that you cannot remove the css file /.resources/mtk/css/normalize-3.0.3.css. However, as a workaround, you could do something like this:

/my-module/decorations/mtk/templates/pages/basic.cssFiles.yaml
normalize:
  link: ""