Clameurs/sites/all/modules/contrib/fields/cer/help/presets.html

<p>When you install CER, it won’t do anything at all until you create at least
one <dfn>preset</dfn>. A preset is a relationship between two reference field
instances, which are referred to as the left and right fields, respectively.
When a change occurs in the left field, the right field will react &mdash; and
vice-versa.</p>

<p>An example: suppose you have a user reference field called Author, and it 
lives on Page nodes. You also have a node reference field called My Pages, and 
it lives on users. You can set up a preset that looks like this:</p>

<p>Node: Page: Author &lt;--&gt; User: My Pages</p>

<p>In this case, Author is the left field and My Pages is the right field. When
the Author field is changed on a Page node, the referenced user(s) will be
given a back-reference to that node.</p>

<p>By default, presets are <dfn>bidirectional</dfn>. This means that a change 
on either side of the preset will affect the other side. The previous example 
is bidirectional: you can change Author or My Pages, and the other side 
will react accordingly.</p>

<p>It's possible to make a preset <dfn>one-directional</dfn>, which means that 
the right side will react when the left side changes, but NOT the other way 
around. In a one-directional preset, changes to the right field will have no 
effect on the left field.</p>

<p>A one-directional version of the above example would look like this:</p>

<p>Node: Page: Author —&gt; User: My Pages</p>

<p>So what this means is that, in a bidirectional preset, it really doesn't 
matter which field is the left one and which is the right one. They’ll affect 
each other equally. But in a one-directional preset, it <em>does</em> matter 
which side you're on. CER allows you to &quot;invert&quot; (flip) a 
one-directional preset.</p>

<p>Internally, CER treats all reference-type fields the same way, which allows 
you to put a different kind of field on either side of a preset. You don't 
have to necessarily relate a node reference field to another node reference 
field. You could relate a node reference field to a user reference field. The 
only restriction is that each side of the preset must be able to reference the 
other side. So, to again use our example, Author needs to be able to reference 
users, and My Pages needs to be able to reference nodes (of the Page type). 
CER won't let you create relationships between fields that can’t actually 
relate.</p>

<p>CER presets are entities built on top of Entity API, and they can be 
imported and exported just like any other exportable entity type, including
support for Features.</p>