OpenBlock v1.1.0 documentation

Creating a Custom NewsItem Schema

In OpenBlock lingo, a Schema is a type of NewsItem. (It's a good idea to read Brief Overview: Concepts and Terminology if you haven't.)

OpenBlock's ebpub package provides several models for defining Schemas. This section provides a brief example of creating a Schema, defining its custom fields, and creating a NewsItem with the Schema.

It is assumed for this section that you have installed either the demo or have created a custom application.

For background and additional detail, see also SchemaFields and Attributes in the ebpub documentation, the code in ebpub.db.models and the video

Cleaning Up After Experiments

Typically it will take you a little while to settle on a schema you like, and you may accumulate some junk newsitems while testing. It's often useful to clean these up and start fresh. There is a script at ebpub/db/bin/ that can delete all NewsItems of a given Schema, plus all their Attributes and Lookups.

Experimenting with Existing Schemas

When running syncdb --migrate with 'ebpub' in settings.INSTALLED_APPS, a few default schemas will be loaded for you: a basic 'Local News' type, and an 'Open311 Service Requests' type.

If you also have obdemo in settings.INSTALLED_APPS, you will get the schemas that are used by our Boston demo, including: Boston events, restaurant inspections, building permits, and Boston police reports.

You may wish to look at these in the admin UI to see how they're configured. Some of them might be appropriate for your purposes out of the box or with slight modifications.

You can of course use the admin UI to delete any that you don't want to use.

Note that modifications and deletions are permanent. We don't have an "undo" feature, sorry.

Make a Schema From Scratch

For this example, we will model a "Crime Report". Beyond the basic NewsItem information, like title, date, location etc, we will want to record some custom information with each report:

  • Responding officer's name
  • Type of crime (in english)
  • Police code for crime

Steps are shown using the django shell, but this could also be performed in a script, or similar steps in the administrative interface. This code can also be found in misc/examples/ This section assumes your application is myblock; substitute your own or obdemo for the demo application. Start in the root of your virtual env:

$ source bin/activate
$ shell --settings=myblock.settings
Python 2.6.1 (r261:67515, Feb 11 2010, 00:51:29)
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

Creating the Schema

The first step is to create an ebpub.db.models.Schema to represent the Crime Report type:

>>> from ebpub.db.models import Schema
>>> crime_report = Schema()

This object will contain metadata about all Crime Reports, like what its title is and how to pluralize it:

>>> crime_report.indefinite_article = 'a'
>>> = "Crime Report"
>>> crime_report.plural_name = "Crime Reports"

The slug is the unique identifier for this Schema that will be used in URLs on the site. It should be brief and contain URL safe characters:

>>> crime_report.slug = 'crimereport'

The min_date field can be used to limit how far back the user can navigate when viewing crime reports. For now, we'll just assume that everything is in the future:

>>> from datetime import datetime
>>> crime_report.min_date = datetime.utcnow()

The last_updated field tracks when we last checked for new crime reports. We'll also just stub this out to the current time for now:

>>> crime_report.last_updated = datetime.utcnow()

The has_newsitem_detail field controls whether this item has a page hosted on this site, or whether it has its own external url. We'll host these ourselves:

>>> crime_report.has_newsitem_detail = True

The is_public field controls whether or not NewsItems of this type are visible to anybody other than administrators on the site. Normally you should wait until the type is set up and loaded with news before "turning it on". We'll just make it available immediately:

>>> crime_report.is_public = True

The is_event field controls whether or not NewsItems of this type are announcements of future events, rather than news that happened in the past. For more details on how to do this, see Event-like News Types This doesn't apply to crime reports, so we'll leave it set to False:

>>> crime_report.is_event = False

There are a few additional fields you can explore (see the code in ebpub.db.models.Schema), but this will be good enough to start with. So let's save it and move on:


At this point you will be able to see the type listed on your site's front page, and reach an (empty) listing using your slug by visiting assuming you are running the web server.

Making Maps Prettier

If you want your different NewsItem types to stand out from each other on maps, you have two options.

You can set your schema's map_color to a hex color code (eg. #FF0000), and markers for that news type will be filled with that color.

Or, you can set your schema's map_icon_url to the URL of an image to use for its markers. Should be roughly 35x35 pixels. (If you are hosting your own map icons, it's fine to use a relative URL here.)

OpenBlock does not currently ship with any map icons. One source of good free (Creative Commons 3.0 BY-SA) map icons is .

Adding Custom Fields

As mentioned earlier, we will add the following custom fields:

  • Responding officer's name
  • Type of crime (in english)
  • Police code for crime

We will create an ebpub.db.models.SchemaField to describe each custom field. Let's start with the reporting officer:

>>> from ebpub.db.models import SchemaField
>>> officer = SchemaField()
>>> officer.schema = crime_report
>>> officer.pretty_name = "Reporting Officer's Name"
>>> officer.pretty_name_plural = "Reporting Officer's Names"

The values of all the custom fields for a particular NewsItem will be stored in a single ebpub.db.models.Attribute object. The Attribute object has a fixed set of fields which can be used for custom attributes. The fields are named according to their type, and numbered:

Names Possible Numbers Type
varcharNN 01 - 05 models.CharField (length 255)
dateNN 01 - 05 models.DateField
timeNN 01 - 02 models.TimeField
datetimeNN 01 - 04 models.DateTimeField
boolNN 01 - 05 models.NullBooleanField
intNN 01 - 07 models.IntegerField
textNN 01 models.TextField

Each SchemaField will map onto one of the fields of the Attribute class. We'll map the reporting officer onto the first varchar field varchar01 by setting the real_name attribute:

>>> officer.real_name = 'varchar01'

When working with a crime report NewsItem, we'll want to have an alias for this attribute in the code, so we don't always have to remember what 'varchar01' means for crime reports. This is set using the name field of the SchemaField. We'll call it officer, and move on:

>>> = 'officer'

That's the important stuff. There are a bunch of mandatory display-related fields; we'll just gloss over these for now:

>>> officer.display = True
>>> officer.display_order = 10
>>> officer.is_searchable = True
>>> officer.is_lookup = False
>>> officer.is_filter = False
>>> officer.is_charted = False

Now we can save this SchemaField:


The name of the crime works the same way, but we'll need to store it in a different field. We'll use the second varchar field, varchar02:

>>> crime_name = SchemaField()
>>> crime_name.schema = crime_report
>>> crime_name.real_name = "varchar02"
>>> crime_name.pretty_name = "Crime Type"
>>> crime_name.pretty_plural_name = "Crime Types"
>>> = "crime_type"
>>> crime_name.display = True
>>> crime_name.display_order = 10
>>> crime_name.is_searchable = True
>>> crime_name.is_lookup = False
>>> crime_name.is_filter = False
>>> crime_name.is_charted = False

For the crime code, we'll use an integer field:

>>> crime_code = SchemaField()
>>> crime_code.schema = crime_report
>>> crime_code.real_name = "int01"
>>> crime_code.pretty_name = "Crime Code"
>>> crime_code.pretty_plural_name = "Crime Codes"
>>> = "crime_code"
>>> crime_code.display = True
>>> crime_code.display_order = 10
>>> crime_code.is_searchable = True
>>> crime_code.is_lookup = False
>>> crime_code.is_filter = False
>>> crime_code.is_charted = False

Phew, okay we just designed a NewsItem type!

Creating a NewsItem with the Schema

Now we can finally start churning out amazing crime reports. We start by making a basic news item with our schema and filling out the basic fields:

>>> from ebpub.db.models import NewsItem
>>> report = NewsItem()
>>> report.schema = crime_report
>>> report.title = "Hooligans causing disturbance downtown"
>>> report.location_name = "123 Fakey St."
>>> report.item_date = datetime.utcnow()
>>> report.pub_date = datetime.utcnow()
>>> report.description = "Blah Blah Blah"

Great, now (any only now) we can set the extra fields, which are weirdly immediately set when accessing the special attributes dictionary on the NewsItem. (There is some python magic going on, see the code in ebpub.db.models.) We use the names that we assigned when we were designing the schema:

>>> report.attributes['officer'] = "John Smith"
>>> report.attributes['crime_type'] = "Disturbing The Peace"
>>> report.attributes['crime_code'] = 187

If you visit the crime reports page at it should list your new item. You can click its link to view the custom details you added.


Lookups: normalized enums

For attributes that have only a few possible values, you can add another layer of indirection called a Lookup to confuse you... err, normalize the data somewhat. See Lookups for more.