Setting up relationships, referred to as associations, between different types of nodes is useful when modelling a specific domain.
There are quite a few API calls involved in managing associations between nodes in the repository:
| API Call | Description | API Explorer |
|---|---|---|
| GET nodes/{parentId}/children | List the parent-to-primary-child associations (i.e. cm:contains) for a parent node. | http://localhost:8080/api-explorer/#!/nodes/listNodeChildren |
| POST nodes/{parentId}/children | Create a new parent-to-primary-child association (i.e. cm:contains) for a parent node. | http://localhost:8080/api-explorer/#!/nodes/createNode |
| GET nodes/{parentId}/secondary-children | List the parent-to-secondary-child associations for a parent node. | http://localhost:8080/api-explorer/#!/nodes/listSecondaryChildren |
| GET nodes/{childId}/parents | Get a list of parent nodes that are associated with a child node. | http://localhost:8080/api-explorer/#!/nodes/listParents |
| POST nodes/{parentId}/secondary-children | Create a new parent-to-secondary-child association for a parent node. | http://localhost:8080/api-explorer/#!/nodes/createSecondaryChildAssociation |
| DELETE /nodes/{parentId}/secondary-children/{childId} | Delete a parent-to-secondary-child association. | http://localhost:8080/api-explorer/#!/nodes/deleteSecondaryChildAssociation |
| GET nodes/{sourceId}/targets | List the peer-to-peer associations for a source node. | http://localhost:8080/api-explorer/#!/nodes/listTargetAssociations |
| GET nodes/{targetId}/sources | Get a list of source nodes that are associated with a target node. | http://localhost:8080/api-explorer/#!/nodes/listSourceAssociations |
| POST nodes/{sourceId}/targets | Create a new peer-to-peer association for a source node. | http://localhost:8080/api-explorer/#!/nodes/createAssociation |
| DELETE /nodes/{sourceId}/targets/{targetId} | Delete a peer-to-peer association. | http://localhost:8080/api-explorer/#!/nodes/deleteSecondaryChildAssociation |
When working with content, it’s important to be able to set up relationships such as folder to files and file to file. These relationships are referred to as associations in the Alfresco content model. Out of the box you have already worked with a folder to folders and files association, which is used to build the folder hierarchy that you see in the UI clients. This association is called cm:contains and is part of the cm:folder type:
<typename="cm:folder">
<title>Folder</title>
<parent>cm:cmobject</parent>
<archive>true</archive>
<associations>
<child-association name="cm:contains">
<source>
<mandatory>false</mandatory>
<many>true</many>
</source>
<target>
<class>sys:base</class>
<mandatory>false</mandatory>
<many>true</many>
</target>
<duplicate>false</duplicate>
<propagateTimestamps>true</propagateTimestamps>
</child-association>
</associations>
</type>
This association is of the type child-association, which means that if you delete the folder the contained folders and files will also be automatically deleted. There is also a peer-to-peer association type that you can see an example of in the out-of-the-box cm:person type definition:
<typename="cm:person">
<title>Person</title>
<parent>cm:authority</parent>
<properties>
...
</properties>
<associations>
<association name="cm:avatar">
<source>
<role>cm:avatarOf</role>
<mandatory>false</mandatory>
<many>false</many>
</source>
<target>
<class>cm:content</class>
<role>cm:hasAvatar</role>
<mandatory>false</mandatory>
<many>false</many>
</target>
</association>
</associations>
</type>
The peer-to-peer association type is called just association. If you delete a person node the associated avatar will not be automatically deleted.
An association is built up of a source and a target definition, and the source is basically the class (i.e. type or aspect) that defines the association. You can use the mandatory and many properties to define the cardinality for the association.
When you work with the cm:contains association type you set up what is referred to as primary parent-child associations. This is what happens when you upload a file or create a folder. There is also the possibility to work with other types of child associations, they are then referred to as secondary child associations. We will have a look at them now.