24. Behaviors

In this part you will:

  • Add another field to talks by using a behavior

  • Add a custom index for the field

  • Add a metadata column for the field

Topics covered:

  • Behaviors

  • Indexes

  • Metacolumns

You can extend the functionality of your Dexterity object by writing an adapter that adapts your dexterity object to add another feature or aspect.

But if you want to use this adapter, you must somehow know that an object implements that. Also, adding more fields to an object would not be easy with such an approach.

24.1. Dexterity Approach

Dexterity has a solution for it, with special adapters that are called and registered by the name behavior.

A behavior can be added to any content type through the web and at runtime.

All default views (e.g. the add- and edit-forms) know about the concept of behaviors. When rendering forms, the views also check whether there are behaviors referenced with the current context and if these behaviors have a schema of their own, these fields get shown in addition.

24.2. Names and Theory

The name behavior is not a standard term in software development. But it is a good idea to think of a behavior as an aspect. You are adding an aspect to your content type and you want to write your aspect in such a way that it works independently of the content type on which the aspect is applied. You should not have dependencies to specific fields of your object or to other behaviors.

Such an object allows you to apply the open/closed principle to your dexterity objects.

24.3. Practical example

Note

You can also use the Plone Command Line Tool plonecli to initially create a behavior and edit it afterwards

So, let us write our own small behavior.

We want some talks, news items or other content to be represented on the frontpage similar to what we did with the “hot news” field early on.

So for now, our behavior just adds a new field to store this information.

We want to keep a clean structure, so we create a behaviors directory first, and include it into the zcml declarations of our configure.zcml.

<include package=".behaviors" />

Then, we add an empty behaviors/__init__.py and a behaviors/configure.zcml containing

And a behaviors/featured.py containing:

This is exactly the same type of schema as the one in the talk content-type. The only addition is @provider(IFormFieldProvider) that makes sure that the fields in the schema are displayed in the add- and edit-forms.

Let’s go through this step by step.

  1. We register a behavior in behaviors/configure.zcml. We do not say for which content type this behavior is valid. You do this through the web or in the GenericSetup profile.

  2. We create a interface in behaviors/featured.py for our behavior. We make it also a schema containing the fields we want to declare. We could just define schema fields on a zope.interface class, but we use an extended form from plone.supermodel, else we could not use the fieldset features.

  3. We mark our schema as a class that also provides the IFormFieldProvider interface using a decorator. The schema class itself provides the interface, not its instance!

  4. We also add a fieldset so that our fields are not mixed with the normal fields of the object.

  5. We add a normal Bool schema field to control if a item should be displayed on the frontpage.

24.4. Adding it to our talk

We could add this behavior now via the plone control panel. But instead, we will do it directly and properly in our GenericSetup profile

We must add the behavior to profiles/default/types/talk.xml:

 1<?xml version="1.0"?>
 2<object name="talk" meta_type="Dexterity FTI" i18n:domain="plone"
 3   xmlns:i18n="http://xml.zope.org/namespaces/i18n">
 4   ...
 5 <property name="behaviors">
 6  <element value="plone.dublincore"/>
 7  <element value="plone.namefromtitle"/>
 8  <element value="ploneconf.featured"/>
 9 </property>
10 ...
11</object>

After a restart and the reinstallation of the product we now have the new field we added through the behavior:

Extended behavior field shown in Volto

24.5. Add a index for the new field

To use these new information for example in searches or listings we have to add an index to the plone_catalog for it. Indexing is the action to make object data search-able. Plone stores available indexes in the database.

Note

You can create them through-the-web and inspect existing indexes in portal_catalog on Index tab. To have those indexes directly after the installation you have to add those indexes like we will show in this chapter.

First of all we have to decide which kind of Index we need to add for our new field. Often used index types are for example:

  • FieldIndex stores values as is

  • BooleanIndex stores boolean values as is

  • KeywordIndex allows keyword-style look-ups (query term is matched against all the values of a stored list)

  • DateIndex and DateRangeIndex store dates (Zope 2 DateTime objects) in searchable format. The latter provides ranged searches.

Therefore we have a boolean field for the featured information it would be obvious to use the BooleanIndex for this.

To add a new index we have to change the catalog.xml in the profiles/default folder of our product. Without changes the file should look like this:

1<?xml version="1.0"?>
2<object name="portal_catalog">
3  <!--<column value="my_meta_column"/>-->
4</object>

To add the new BooleanIndex to the file we have to change the file as following:

1<?xml version="1.0"?>
2<object name="portal_catalog">
3  <index name="featured" meta_type="BooleanIndex">
4    <indexed_attr value="featured"/>
5  </index>
6</object>

To understand this snippet we have to understand the tags and information we are using:

  • The index-tag will tell the plone_catalog that we want to add a new index

  • name will be shown in the overview of portal_catalog and can be used in listings and searches later on

  • meta_type will determine the kind of index we want to use

  • The indexed_attr will include the fieldname of the information we are going to save in the index

After a restart and reinstallation of the product, it should now create a new index in the portal_catalog.

Note

Instead of deinstall/install or reinstall the product over the prtal_quickinstaller or Add-Ons controlpanel, we can import new or altered XML files in the ZMI. To do so go to portal_setup, switch to the Import-Tab and search for the profile to import like in this case: ploneconf.site.

To see if the adding was successfully we will open the ZMI of our plone-site and navigate to the portal_catalog and click the Indexes-Tab. In the above list the new index fetaured should pop up.

24.6. Add a metadata column for the new field

The same rules and methods shown above for indexes apply for metadata columns. The difference with metadata is that it is not used for searching, but for displaying the results.

To add a metadata column for featured we have to add one more line in the catalog.xml like this:

1<?xml version="1.0"?>
2<object name="portal_catalog">
3  <index name="featured" meta_type="BooleanIndex">
4    <indexed_attr value="featured"/>
5  </index>
6  <column value="featured"/>
7</object>

After another restart and another import of the xml-profile the new metadata column can be found in the portal_catalog in your ZMI under the tab Metadata.

24.7. Exercises

Since you now know how to add indexes to the portal_catalog it is time for some exercise.

24.7.1. Exercise 1

Add a new index for the speaker-field of our content type Talk

Solution

1<?xml version="1.0"?>
2<object name="portal_catalog">
3  <index name="featured" meta_type="BooleanIndex">
4    <indexed_attr value="featured"/>
5  </index>
6  <index name="speaker" meta_type="FieldIndex">
7    <indexed_attr value="speaker"/>
8  </index>
9</object>