The CKAN DataStore extension provides an ad hoc database for storage of structured data from CKAN resources. Data can be pulled out of resource files and stored in the DataStore.
When a resource is added to the DataStore, you get:
- Automatic data previews on the resource's page, using the
Data Explorer extension <data-explorer> - The DataStore API: search, filter and update the data, without having to download and upload the entire data file
The DataStore is integrated into the CKAN API </api/index> and authorization system.
The DataStore is generally used alongside the DataPusher, which will automatically upload data to the DataStore from suitable files, whether uploaded to CKAN's FileStore or externally linked.
The DataStore is distinct but complementary to the FileStore (see filestore). In contrast to the FileStore which provides 'blob' storage of whole files with no way to access or query parts of that file, the DataStore is like a database in which individual data elements are accessible and queryable. To illustrate this distinction, consider storing a spreadsheet file like a CSV or Excel document. In the FileStore this file would be stored directly. To access it you would download the file as a whole. By contrast, if the spreadsheet data is stored in the DataStore, one would be able to access individual spreadsheet rows via a simple web API, as well as being able to make queries over the spreadsheet contents.
Note
The DataStore requires PostgreSQL 9.0 or later. It is possible to use the DataStore on versions prior to 9.0 (for example 8.4). However, the ~ckanext.datastore.logic.action.datastore_search_sql will not be available and the set-up is slightly different. Make sure, you read legacy-mode for more details.
Add the datastore plugin to your CKAN config file:
ckan.plugins = datastoreWarning
Make sure that you follow the steps in Set Permissions below correctly. Wrong settings could lead to serious security issues.
The DataStore requires a separate PostgreSQL database to save the DataStore resources to.
List existing databases:
sudo -u postgres psql -lCheck that the encoding of databases is UTF8, if not internationalisation may be a problem. Since changing the encoding of PostgreSQL may mean deleting existing databases, it is suggested that this is fixed before continuing with the datastore setup.
Tip
If your CKAN database and DataStore databases are on different servers, then you need to create a new database user on the server where the DataStore database will be created. As in installing/install-from-source we'll name the database user :
sudo -u postgres createuser -S -D -R -P -l
Create a database_user called . This user will be given read-only access to your DataStore database in the Set Permissions step below:
sudo -u postgres createuser -S -D -R -P -l
Create the database (owned by ), which we'll call :
sudo -u postgres createdb -O -E utf-8
Now, uncomment the ckan.datastore.write_url and ckan.datastore.read_url lines in your CKAN config file and edit them if necessary, for example:
ckan.datastore.write_url = postgresql://:pass@localhost/|datastore| ckan.datastore.read_url = postgresql://:pass@localhost/|datastore|
Replace pass with the passwords you created for your and database users.
Tip
See legacy-mode if these steps continue to fail or seem too complicated for your set-up. However, keep in mind that the legacy mode is limited in its capabilities.
Once the DataStore database and the users are created, the permissions on the DataStore and CKAN database have to be set. CKAN provides a paster command to help you correctly set these permissions.
If you are able to use the psql command to connect to your database as a superuser, you can use the datastore set-permissions command to emit the appropriate SQL to set the permissions.
For example, if you can connect to your database server as the postgres superuser using:
sudo -u postgres psqlThen you can use this connection to set the permissions:
sudo ckan datastore set-permissions |
sudo -u postgres psql --set ON_ERROR_STOP=1Note
If you performed a source install, you will need to replace all references to sudo ckan ... with paster --plugin=ckan ...
If your database server is not local, but you can access it over SSH, you can pipe the permissions script over SSH:
sudo ckan datastore set-permissions |
ssh dbserver sudo -u postgres psql --set ON_ERROR_STOP=1If you can't use the psql command in this way, you can simply copy and paste the output of:
sudo ckan datastore set-permissionsinto a superuser console.
The DataStore is now set-up. To test the set-up, (re)start CKAN and run the following command to list all DataStore resources:
curl -X GET "http://127.0.0.1:5000/api/3/action/datastore_search?resource_id=_table_metadata"This should return a JSON page without errors.
To test the whether the set-up allows writing, you can create a new DataStore resource. To do so, run the following command:
curl -X POST http://127.0.0.1:5000/api/3/action/datastore_create -H "Authorization: {YOUR-API-KEY}" -d '{"resource": {"package_id": "{PACKAGE-ID}"}, "fields": [ {"id": "a"}, {"id": "b"} ], "records": [ { "a": 1, "b": "xyz"}, {"a": 2, "b": "zzz"} ]}'Replace {YOUR-API-KEY} with a valid API key and {PACKAGE-ID} with the id of an existing CKAN dataset.
A table named after the resource id should have been created on your DataStore database. Visiting this URL should return a response from the DataStore with the records inserted above:
http://127.0.0.1:5000/api/3/action/datastore_search?resource_id={RESOURCE_ID}Replace {RESOURCE-ID} with the resource id that was returned as part of the response of the previous API call.
You can now delete the DataStore table with:
curl -X POST http://127.0.0.1:5000/api/3/action/datastore_delete -H "Authorization: {YOUR-API-KEY}" -d '{"resource_id": "{RESOURCE-ID}"}'To find out more about the DataStore API, see The DataStore API.
Tip
The legacy mode can also be used to simplify the set-up since it does not require you to set the permissions or create a separate user.
The DataStore can be used with a PostgreSQL version prior to 9.0 in legacy mode. Due to the lack of some functionality, the ~ckanext.datastore.logic.action.datastore_search_sql and consequently the datastore_search_htsql cannot be used. To enable the legacy mode, remove the declaration of the ckan.datastore.read_url.
The set-up for legacy mode is analogous to the normal set-up as described above with a few changes and consists of the following steps:
- Enable the plugin
- The legacy mode is enabled by not setting the
ckan.datastore.read_url - Set-Up the database
- Create a separate database
- Create a write user on the DataStore database (optional since the CKAN user can be used)
- Test the set-up
There is no need for a read-only user or special permissions. Therefore the legacy mode can be used for simple set-ups as well.
Often, one wants data that is added to CKAN (whether it is linked to or uploaded to the FileStore <filestore>) to be automatically added to the DataStore. This requires some processing, to extract the data from your files and to add it to the DataStore in the format the DataStore can handle.
This task of automatically parsing and then adding data to the DataStore is performed by the DataPusher, a service that runs asynchronously and can be installed alongside CKAN.
To install this please look at the docs here: http://docs.ckan.org/projects/datapusher
The CKAN DataStore offers an API for reading, searching and filtering data without the need to download the entire file first. The DataStore is an ad hoc database which means that it is a collection of tables with unknown relationships. This allows you to search in one DataStore resource (a table in the database) as well as queries across DataStore resources.
Data can be written incrementally to the DataStore through the API. New data can be inserted, existing data can be updated or deleted. You can also add a new column to an existing table even if the DataStore resource already contains some data.
You will notice that we tried to keep the layer between the underlying PostgreSQL database and the API as thin as possible to allow you to use the features you would expect from a powerful database management system.
A DataStore resource can not be created on its own. It is always required to have an associated CKAN resource. If data is stored in the DataStore, it will automatically be previewed by the recline preview extension <data-explorer>.
Making a DataStore API request is the same as making an Action API request: you post a JSON dictionary in an HTTP POST request to an API URL, and the API also returns its response in a JSON dictionary. See the /api/index for details.
Note
Lists can always be expressed in different ways. It is possible to use lists, comma separated strings or single items. These are valid lists: ['foo', 'bar'], 'foo, bar', "foo", "bar" and 'foo'. Additionally, there are several ways to define a boolean value. True, on and 1 are all vaid boolean values.
Note
The table structure of the DataStore is explained in db_internals.
ckanext.datastore.logic.action
A DataStore resource can be downloaded in the CSV file format from {CKAN-URL}/datastore/dump/{RESOURCE-ID}.
Fields define the column names and the type of the data in a column. A field is defined as follows:
{
"id": # a string which defines the column name
"type": # the data type for the column
}Field types are optional and will be guessed by the DataStore from the provided data. However, setting the types ensures that future inserts will not fail because of wrong types. See valid-types for details on which types are valid.
Example:
[
{
"id": "foo",
"type": "int4"
},
{
"id": "bar"
# type is optional
}
]A record is the data to be inserted in a DataStore resource and is defined as follows:
{
"<id>": # data to be set
# .. more data
}Example:
[
{
"foo": 100,
"bar": "Here's some text"
},
{
"foo": 42
}
]The DataStore supports all types supported by PostgreSQL as well as a few additions. A list of the PostgreSQL types can be found in the type section of the documentation. Below you can find a list of the most common data types. The json type has been added as a storage for nested data.
In addition to the listed types below, you can also use array types. They are defines by prepending a _ or appending [] or [n] where n denotes the length of the array. An arbitrarily long array of integers would be defined as int[].
- text
Arbitrary text data, e.g.
Here's some text.- json
Arbitrary nested json data, e.g
{"foo": 42, "bar": [1, 2, 3]}. Please note that this type is a custom type that is wrapped by the DataStore.- date
Date without time, e.g
2012-5-25.- time
Time without date, e.g
12:42.- timestamp
Date and time, e.g
2012-10-01T02:43Z.- int
Integer numbers, e.g
42,7.- float
Floats, e.g.
1.61803.- bool
Boolean values, e.g.
true,0
You can find more information about the formatting of dates in the date/time types section of the PostgreSQL documentation.
A resource in the DataStore can have multiple aliases that are easier to remember than the resource id. Aliases can be created and edited with the ~ckanext.datastore.logic.action.datastore_create API endpoint. All aliases can be found in a special view called _table_metadata. See db_internals for full reference.
The ckanext-htsql extension adds an API action that allows a user to search data in a resource using the HTSQL query expression language. Please refer to the extension documentation to know more.
The DataStore supports querying with multiple API endpoints. They are similar but support different features. The following list gives an overview of the different methods.
| .. | ~ckanext.datastore.logic.action.datastore_search |
~ckanext.datastore.logic.action.datastore_search_sql |
HTSQL<datastore_search_htsql> |
|---|---|---|---|
| Ease of use | Easy | Complex | Medium |
| Flexibility | Low | High | Medium |
| Query language | Custom (JSON) | SQL | HTSQL |
| Join resources | No | Yes | No |
The DataStore is a thin layer on top of a PostgreSQL database. Each DataStore resource belongs to a CKAN resource. The name of a table in the DataStore is always the resource id of the CKAN resource for the data.
As explained in resource-aliases, a resource can have mnemonic aliases which are stored as views in the database.
All aliases (views) and resources (tables respectively relations) of the DataStore can be found in a special view called _table_metadata. To access the list, open http://{YOUR-CKAN-INSTALLATION}/api/3/action/datastore_search?resource_id=_table_metadata.
_table_metadata has the following fields:
- _id
Unique key of the relation in
_table_metadata.- alias_of
Name of a relation that this alias point to. This field is
nulliff the name is not an alias.- name
Contains the name of the alias if alias_of is not null. Otherwise, this is the resource id of the CKAN resource for the DataStore resource.
- oid
The PostgreSQL object ID of the table that belongs to name.