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DataStore extension

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:

The DataStore is integrated into the :doc:`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.

Relationship to FileStore

The DataStore is distinct but complementary to the FileStore (see :doc:`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.

Setting up the DataStore

Note

The DataStore (like CKAN) requires |postgres| 9.2 or later. This was released in 2012, is widely available. At the time of writing, the only version that is not supported by CKAN that has not been made 'end-of-life' by the |postgres| community is 9.1.

.. versionchanged:: 2.6

   Previous CKAN (and DataStore) versions were compatible with earlier versions
   of |postgres|.

1. Enable the plugin

Add the datastore plugin to your CKAN config file:

ckan.plugins = datastore

2. Set-up the database

Warning

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 -l

Check 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.

Create users and databases

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 :doc:`installing/install-from-source` we'll name the database user |database_user|:

sudo -u postgres createuser -S -D -R -P -l |database_user|

Create a database_user called |datastore_user|. 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 |datastore_user|

Create the database (owned by |database_user|), which we'll call |datastore|:

sudo -u postgres createdb -O |database_user| |datastore| -E utf-8

Set URLs

Now, uncomment the :ref:`ckan.datastore.write_url` and :ref:`ckan.datastore.read_url` lines in your CKAN config file and edit them if necessary, for example:

ckan.datastore.write_url = postgresql://|database_user|:pass@localhost/|datastore|
ckan.datastore.read_url = postgresql://|datastore_user|:pass@localhost/|datastore|

Replace pass with the passwords you created for your |database_user| and |datastore_user| database users.

Set permissions

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 psql

Then you can use this connection to set the permissions:

sudo ckan datastore set-permissions | sudo -u postgres psql --set ON_ERROR_STOP=1

Note

If you performed a source install, you will need to replace all references to sudo ckan ... with paster --plugin=ckan ... and provide the path to the config file, e.g. paster --plugin=ckan datastore set-permissions -c /etc/ckan/default/development.ini | sudo -u postgres psql --set ON_ERROR_STOP=1

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=1

If you can't use the psql command in this way, you can simply copy and paste the output of:

sudo ckan datastore set-permissions

into a |postgres| superuser console.

3. Test the set-up

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.

DataPusher: Automatically Add Data to the DataStore

Often, one wants data that is added to CKAN (whether it is linked to or uploaded to the :doc:`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

Note

The DataPusher only imports the first worksheet of a spreadsheet. It also does not support duplicate column headers. That includes blank column headings.

Data Dictionary

DataStore columns may be described with a Data Dictionary. A Data Dictionary tab will appear when editing any resource with a DataStore table. The Data Dictionary form allows entering the following values for each column:

  • Type Override: the type to be used the next time DataPusher is run to load data into this column
  • Label: a human-friendly label for this column
  • Description: a full description for this column in markdown format

Extension developers may add new fields to this form by overriding the default Data Dictionary form template datastore/snippets/dictionary_form.html.

The Data Dictionary is set through the API as part of the :ref:`fields` passed to :meth:`~ckanext.datastore.logic.action.datastore_create` and returned from :meth:`~ckanext.datastore.logic.action.datastore_search`.

Downloading Resources

A DataStore resource can be downloaded in the CSV file format from {CKAN-URL}/datastore/dump/{RESOURCE-ID}.

For an Excel-compatible CSV file use {CKAN-URL}/datastore/dump/{RESOURCE-ID}?bom=true.

Other formats supported include tab-separated values (?format=tsv), JSON (?format=json) and XML (?format=xml). E.g. to download an Excel-compatible tab-separated file use {CKAN-URL}/datastore/dump/{RESOURCE-ID}?format=tsv&bom=true.

The DataStore API

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.

Triggers may be added to enforce validation, clean data as it is loaded or even record histories. Triggers are PL/pgSQL functions that must be created by a sysadmin.

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 :ref:`recline preview extension <data-explorer>`.

Making a DataStore API request

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 :doc:`/api/index` for details.

API reference

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 :ref:`db_internals`.

.. automodule:: ckanext.datastore.logic.action
   :members:


Fields

Fields define the column names and the type of the data in a column. A field is defined as follows:

{
    "id":  # the column name (required)
    "type":  # the data type for the column
    "info": {
        "label":  # human-readable label for column
        "notes":  # markdown description of column
        "type_override":  # type for datapusher to use when importing data
        ...:  # other user-defined fields
    }
}

Field types not provided will be guessed based on the first row of provided data. Set the types to ensure that future inserts will not fail because of an incorrectly guessed type. See :ref:`valid-types` for details on which types are valid.

Extra "info" field values will be stored along with the column. "label", "notes" and "type_override" can be managed from the default :ref:`data_dictionary` form. Additional fields can be stored by customizing the Data Dictionary form or by passing their values to the API directly.

Example:

[
    {
        "id": "code_number",
        "type": "numeric"
    },
    {
        "id": "description"
        "type": "text",
        "info": {
            "label": "Description",
            "notes": "A brief usage description for this code",
            "example": "Used for temporary service interruptions"
        }
    }
]

Records

A record is the data to be inserted in a DataStore resource and is defined as follows:

{
    column_1_id: value_1,
    columd_2_id: value_2,
    ...
}

Example:

[
    {
        "code_number": 10,
        "description": "Submitted successfully"
    },
    {
        "code_number": 42,
        "description": "In progress"
    }
]

Field types

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.

Resource aliases

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 :meth:`~ckanext.datastore.logic.action.datastore_create` API endpoint. All aliases can be found in a special view called _table_metadata. See :ref:`db_internals` for full reference.

HTSQL support

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.

Comparison of different querying methods

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.

  :meth:`~ckanext.datastore.logic.action.datastore_search` :meth:`~ckanext.datastore.logic.action.datastore_search_sql` :ref:`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

Internal structure of the database

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 :ref:`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 null iff 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.

Extending DataStore

Starting from CKAN version 2.7, backend used in DataStore can be replaced with custom one. For this purpose, custom extension must implement ckanext.datastore.interfaces.IDatastoreBackend, which provides one method - register_backends. It should return dictonary with names of custom backends as keys and classes, that represent those backends as values. Each class supposed to be inherited from ckanext.datastore.backend.DatastoreBackend.

Note

Example of custom implementation can be found at ckanext.example_idatastorebackend

.. automodule:: ckanext.datastore.backend
   :members: