Project Open Data extension
by data.gov - GSA

ckanext-datajson

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A CKAN extension containinig plugins datajson. First is used by http://catalog.data.gov/ to harvest data sources from a remote /data.json file according to the U.S. Project Open Data metadata specification (https://project-open-data.cio.gov/).

Plugin datajson provides a harvester to import datasets from other remote /data.json files. See below for setup instructions.

And the plugin also provides a new view to validate /data.json files at http://ckanhostname/pod/validate.

Installation

To install, activate your CKAN virtualenv, install dependencies, and install the module in develop mode, which just puts the directory in your Python path.

. path/to/pyenv/bin/activate
pip install -r pip-requirements.txt
python setup.py develop

Then in your CKAN .ini file, add datajson to your ckan.plugins line:

ckan.plugins = (other plugins here...) datajson

That’s the plugin for /data.json output. To make the harvester available, also add:

ckan.plugins = (other plugins here...) harvest datajson_harvest

If you’re running CKAN via WSGI, we found a strange Python dependency bug. It might only affect development environments. The fix was to revise wsgi.py and add:

import ckanext

before

from paste.deploy import loadapp

Then restart your server and check out:

http://yourdomain.com/data.json
   and
http://yourdomain.com/data.jsonld
   and
http://yourdomain.com/pod/validate  

Caching The Response

If you’re deploying inside Apache, some caching would be a good idea because generating the /data.json file can take a good few moments. Enable the cache modules:

a2enmod cache
a2enmod disk_cache

And then in your Apache configuration add:

CacheEnable disk /data.json
CacheRoot /tmp/apache_cache
CacheDefaultExpire 120
CacheMaxFileSize 50000000
CacheIgnoreCacheControl On
CacheIgnoreNoLastMod On
CacheStoreNoStore On

And be sure to create /tmp/apache_cache and make it writable by the Apache process.

Generating /data.json Off-Line

Generating this file is a little slow, so an alternative instead of caching is to generate the file periodically (e.g. in a cron job). In that case, you’ll want to change the path that CKAN generates the file at to something other than /data.json. In your CKAN .ini file, in the app:main section, add:

ckanext.datajson.path = /internal/data.json

Now create a crontab file (“mycrontab”) to download this URL to a file on disk every ten minutes:

0-59/10 * * * * wget -qO /path/to/static/data.json http://localhost/internal/data.json

And activate your crontab like so:

crontab mycrontab

In Apache, we’ll want to block outside access to the “internal” URL, and also map the URL /data.json to the static file. In your httpd.conf, add:

Alias /data.json /path/to/static/data.json

<Location /internal/>
    Order deny,allow
    Allow from 127.0.0.1
    Deny from all
</Location>

And then restart Apache. Wait for the cron job to run once, then check if /data.json loads (and it should be fast!). Also double check that http://yourdomain.com/internal/data.json gives a 403 forbidden error when accessed from some other location.

Options

You can customize the URL that generates the data.json output:

ckanext.datajson.path = /data.json
ckanext.datajsonld.path = /data.jsonld
ckanext.datajsonld.id = http://www.youragency.gov/data.json

You can enable or disable the Data.json output by setting

ckanext.datajson.url_enabled = False

If ckanext.datajsonld.path is omitted, it defaults to replacing “.json” in your ckanext.datajson.path path with “.jsonld”, so it probably won’t need to be specified.

The option ckanext.datajsonld.id is the @id value used to identify the data catalog itself. If not given, it defaults to ckan.site_url.

The Harvester

To use the data.json harvester, you’ll also need to set up the CKAN harvester extension. See the CKAN harvester README at https://github.com/okfn/ckanext-harvest for how to do that. You’ll set some configuration variables and then initialize the CKAN harvester plugin using:

paster --plugin=ckanext-harvest harvester initdb --config=/path/to/ckan.ini

Now you can set up a new DataJson harvester by visiting:

http://yourdomain.com/harvest

And when configuring the data source, just choose “/data.json” as the source type.

**The next paragraph assumes you’re using my fork of the CKAN harvest extension at https://github.com/JoshData/ckanext-harvest**

In the configuration field, you can put a YAML string containing defaults for fields that may not be set in the source data.json files, e.g. enter something like this:

defaults:
  Agency: Department of Health & Human Services
  Author: Substance Abuse & Mental Health Services Administration
  author_id: http://healthdata.gov/id/agency/samhsa

This again is tied to the HealthData.gov metadata schema.

Credit / Copying

Original work written by the HealthData.gov team. It has been modified in support of Data.gov.

As a work of the United States Government, this package is in the public domain within the United States. Additionally, we waive copyright and related rights in the work worldwide through the CC0 1.0 Universal public domain dedication (which can be found at http://creativecommons.org/publicdomain/zero/1.0/).

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