Content Fragments Support in AEM Assets HTTP API content-fragments-support-in-aem-assets-http-api
Overview overview
Learn about support for Content Fragments in the Assets HTTP API, an important piece of AEM’s headless delivery feature.
- Assets REST API
- including support for Content Fragments
The Assets REST API allows developers for Adobe Experience Manager to access content (stored in AEM) directly over the HTTP API, via CRUD operations (Create, Read, Update, Delete).
The API lets you operate Adobe Experience Manager as a headless CMS (Content Management System) by providing Content Services to a JavaScript front end application. Or any other application that can execute HTTP requests and handle JSON responses.
For example, Single Page Applications (SPA), framework-based or custom, require content provided over the HTTP API, often in JSON format.
While AEM Core Components provide a very comprehensive, flexible and customizable API that can serve required Read operations for this purpose, and whose JSON output can be customized, they do require AEM WCM (Web Content Management) know-how for implementation as they must be hosted in pages that are based on dedicated AEM templates. Not every SPA development organization has direct access to such knowledge.
This is when the Assets REST API can be used. It allows developers to access assets (for example, images and content fragments) directly, without the need to first embed them in a page, and deliver their content in serialized JSON format.
The Assets REST API also allows developers to modify content - by creating new, updating, or deleting existing assets, content fragments and folders.
The Assets REST API:
-
follows the HATEOAS principle
-
implements the SIREN format
Prerequisites prerequisites
The Assets REST API is available on each out-of-the-box install of a recent AEM version.
Key Concepts key-concepts
The Assets REST API offers REST-style access to assets stored within an AEM instance.
It uses the /api/assets
endpoint and requires the path of the asset to access it (without the leading /content/dam
).
- This means that to access the asset at:
/content/dam/path/to/asset
- You need to request:
/api/assets/path/to/asset
For example, to access /content/dam/wknd/en/adventures/cycling-tuscany
, request /api/assets/wknd/en/adventures/cycling-tuscany.json
/api/assets
does not need the use of the.model
selector./content/path/to/page
does require the use of the.model
selector.
The HTTP method determines the operation to be executed:
- GET - to retrieve a JSON representation of an asset or a folder
- POST - to create new assets or folders
- PUT - to update the properties of an asset or folder
- DELETE - to delete an asset or folder
The exact format of supported requests is defined in the API Reference documentation.
Transactional Behavior transactional-behavior
All requests are atomic.
This means that subsequent (write
) requests cannot be combined into a single transaction that could succeed or fail as a single entity.
AEM (Assets) REST API versus AEM Components aem-assets-rest-api-versus-aem-components
(components using Sling Models)
Optimized for consumption in a Single Page Application (SPA), or any other (content consuming) context.
Can also contain layout information.
Create, Read, Update, Delete.
With additional operations depending on the entity type.
Can be accessed directly.
Uses the /api/assets
endpoint, mapped to /content/dam
(in the repository).
An example path would look like: /api/assets/wknd/en/adventures/cycling-tuscany.json
Needs to be referenced through an AEM component on an AEM page.
Uses the .model
selector to create the JSON representation.
An example path would look like:/content/wknd/language-masters/en/adventures/cycling-tuscany.model.json
Multiple options are possible.
OAuth is proposed; can be configured separately from standard setup.
Write access will typically address an author instance.
Read may also be directed to a publish instance.
Security security
If the Assets REST API is used within an environment without specific authentication requirements, AEM’s CORS filter needs to be configured correctly.
In environments with specific authentication requirements, OAuth is recommended.
Available Features available-features
Content Fragments are a specific type of Asset, see Working with Content Fragments.
For further information about features available through the API see:
- The Assets REST API
- Entity Types, where the features specific to each supported type (as relevant to Content Fragments) are explained
Paging paging
The Assets REST API supports paging (for GET requests) via the URL parameters:
offset
- the number of the first (child) entity to retrievelimit
- the maximum number of entities returned
The response will contain paging information as part of the properties
section of the SIREN output. This srn:paging
property contains the total number of (child) entities ( total
), the offset and the limit ( offset
, limit
) as specified in the request.
Example: Paging example-paging
GET /api/assets.json?offset=2&limit=3
...
"properties": {
...
"srn:paging": {
"total": 7,
"offset": 2,
"limit": 3
}
...
}
...
Entity Types entity-types
Folders folders
Folders act as containers for assets and other folders. They reflect the structure of the AEM content repository.
The Assets REST API exposes access to the properties of a folder; for example, its name, title, and so on. Assets are exposed as child entities of folders, and sub-folders.
Assets assets
If an asset is requested, the response will return its metadata; such as title, name and other information as defined by the respective asset schema.
The binary data of an asset is exposed as a SIREN link of type content
.
Assets can have multiple renditions. These are typically exposed as child entities, one exception being a thumbnail rendition, which is exposed as a link of type thumbnail
( rel="thumbnail"
).
Content Fragments content-fragments
A content fragment is a special type of asset. They can be used to access structured data, such as texts, numbers, dates, among others.
As there are several differences to standard assets (such as images or audio), some additional rules apply to handling them.
Representation representation
Content fragments:
-
Do not expose any binary data.
-
Are completely contained in the JSON output (within the
properties
property). -
Are also considered atomic, that is, the elements and variations are exposed as part of the fragment’s properties vs. as links or child entities. This allows for efficient access to the payload of a fragment.
Content Models and Content Fragments content-models-and-content-fragments
Currently the models that define the structure of a content fragment are not exposed through an HTTP API. Therefore the consumer needs to know about the model of a fragment (at least a minimum) - although most information can be inferred from the payload; as data types, and so on. are part of the definition.
To create a content fragment, the (internal repository) path of the model has to be provided.
Associated Content associated-content
Associated content is currently not exposed.
Using using
Usage can differ depending on whether you are using an AEM author or publish environment, together with your specific use case.
-
It is strongly recommended that creation is bound to an author instance (and currently there is no means to replicate a fragment to publish using this API).
-
Delivery is possible from both, as AEM serves requested content in JSON format only.
-
Storage and delivery from an AEM author instance should suffice for behind-the-firewall, media library applications.
-
For live web delivery, an AEM publish instance is recommended.
-
/api
.Read/Delivery read-delivery
Usage is via:
GET /{cfParentPath}/{cfName}.json
For example:
http://<host>/api/assets/wknd/en/adventures/cycling-tuscany.json
The response is serialized JSON with the content structured as in the content fragment. References are delivered as reference URLs.
Two types of read operations are possible:
- Reading a specific content fragment by path, this returns the JSON representation of the content fragment.
- Reading a folder of content fragments by path: this returns the JSON representations of all content fragments within the folder.
Create create
Usage is via:
POST /{cfParentPath}/{cfName}
The body has to contain a JSON representation of the content fragment to be created, including any initial content that should be set on the content fragment elements. It is mandatory to set the cq:model
property and it must point to a valid content fragment model. Failing to do so will result in an error. It is also necessary to add a header Content-Type
which is set to application/json
.
Update update
Usage is via
PUT /{cfParentPath}/{cfName}
The body has to contain a JSON representation of what is to be updated for the given content fragment.
This can simply be the title or description of a content fragment, or a single element, or all element values and/or metadata.
Delete delete
Usage is via:
DELETE /{cfParentPath}/{cfName}
Limitations limitations
There are a few limitations:
- Content fragment models are currently not supported: they cannot be read or created. To be able to create a content fragment, or update an existing one, developers have to know the correct path to the content fragment model. Currently the only method to get an overview of these is through the administration UI.
- References are ignored. Currently there are no checks on whether an existing content fragment is referenced. Therefore, for example, deleting a content fragment might result in issues on a page that contains a reference to the deleted Content Fragment.
- JSON data type The REST API output of the JSON data type is currently string based output.
Status Codes and Error Messages status-codes-and-error-messages
The following status codes can be seen in the relevant circumstances:
-
200 (OK)
Returned when:- requesting a content fragment via
GET
- successfully updating a content fragment via
PUT
- requesting a content fragment via
-
201 (Created)
Returned when:- successfully creating a content fragment via
POST
- successfully creating a content fragment via
-
404 (Not found)
Returned when:- the requested content fragment does not exist
-
500 (Internal server error)
note note NOTE This error is returned: - when an error that cannot be identified with a specific code has happened
- when the given payload was not valid
The following lists common scenarios when this error status is returned, together with the error message (monospace) generated:
-
Parent folder does not exist (when creating a content fragment via
POST
) -
No content fragment model is supplied (cq:model is missing), cannot be read (due to an invalid path or a permission problem) or there is no valid fragment model:
No content fragment model specified
Cannot create a resource of given model '/foo/bar/qux'
-
The content fragment could not be created (potentially a permission problem):
Could not create content fragment
-
Title and or description could not be updated:
Could not set value on content fragment
-
Metadata could not be set:
Could not set metadata on content fragment
-
Content element could not be found or could not be updated
Could not update content element
Could not update fragment data of element
The detailed error messages are usually returned in the following manner:
code language-xml { "class": "core/response", "properties": { "path": "/api/assets/foo/bar/qux", "location": "/api/assets/foo/bar/qux.json", "parentLocation": "/api/assets/foo/bar.json", "status.code": 500, "status.message": "...{error message}.." } }
API Reference api-reference
See here for detailed API references:
Additional Resources additional-resources
For further information see: