How to work with the API - An example¶

Authenticate¶

The OpenEnergy Platform API uses token authentication. Each user has a unique token assigned to it that will be used as an authentication password. You can access you token by visiting you profile on the OEP. In order to issue PUT or POST request you have to include this token in the Authorization-field of your request:

Authorization: Token your-token

Create table¶

We want to create the following table with primary key id:

id: int	name: varchar(50)	geom: geometry(Point)

In order to do so, we send the following PUT request:

PUT oep.iks.cs.ovgu.de/api/v0/schema/sandbox/tables/example_table/
{
    "query": {
        "columns": [
            {
                "name":"id",
                "data_type": "Integer",
                "is_nullable": "NO"
            },{
                "name":"name",
                "data_type": "varchar",
                "character_maximum_length": "50"
            },{
                "name":"geom",
                "data_type": "geometry(point)"
            }
        ],
        "constraints": [
            {
                "constraint_type": "PRIMARY KEY",
                "constraint_parameter": "id",
            }
        ]
    }
}

and include the following headers:

Content-Type: application/json
Authorization: Token your-token

You can use any tool that can send HTTP-requests. E.g. you could use the linux tool curl:

curl
    -X PUT
    -H 'Content-Type: application/json'
    -H 'Authorization: Token <your-token>'
    -d '{
            "query": {
                "columns": [
                    {
                        "name":"id",
                        "data_type": "Integer",
                        "is_nullable": "NO"
                    },{
                        "name":"name",
                        "data_type": "varchar",
                        "character_maximum_length": "50"
                    },{
                        "name":"geom",
                        "data_type": "geometry(point)"
                    }
                ],
                "constraints": [
                    {
                        "constraint_type": "PRIMARY KEY",
                        "constraint_parameter": "id",
                    }
                ]
            }
        }'
    oep.iks.cs.ovgu.de/api/v0/schema/sandbox/tables/example_table/

or python:

>>> import requests
>>> data = { "query": { "columns": [ { "name":"id", "data_type": "serial", "is_nullable": "NO" },{ "name":"name", "data_type": "varchar", "character_maximum_length": "50" },{ "name":"geom", "data_type": "geometry(point)" } ], "constraints": [ { "constraint_type": "PRIMARY KEY", "constraint_parameter": "id" } ] } }
>>> requests.put(oep_url+'/api/v0/schema/sandbox/tables/example_table/', json=data, headers={'Authorization': 'Token %s'%your_token} )
<Response [201]>

If everything went right, you will receive a 201-Resonse and the table has been created.

>>> result = requests.get(oep_url+'/api/v0/schema/sandbox/tables/example_table/columns')
>>> result.status_code
200
>>> json_result = result.json()
>>> json_result['id'] == {'character_maximum_length': None, 'maximum_cardinality': None, 'is_nullable': False, 'data_type': 'integer', 'numeric_precision': 32, 'character_octet_length': None, 'interval_type': None, 'dtd_identifier': '1', 'interval_precision': None, 'numeric_scale': 0, 'is_updatable': True, 'datetime_precision': None, 'ordinal_position': 1, 'column_default': "nextval('sandbox.example_table_id_seq'::regclass)", 'numeric_precision_radix': 2}
True
>>> json_result['geom'] == {'character_maximum_length': None, 'maximum_cardinality': None, 'is_nullable': True, 'data_type': 'USER-DEFINED', 'numeric_precision': None, 'character_octet_length': None, 'interval_type': None, 'dtd_identifier': '3', 'interval_precision': None, 'numeric_scale': None, 'is_updatable': True, 'datetime_precision': None, 'ordinal_position': 3, 'column_default': None, 'numeric_precision_radix': None}
True
>>> json_result['name'] == {'character_maximum_length': 50, 'maximum_cardinality': None, 'is_nullable': True, 'data_type': 'character varying', 'numeric_precision': None, 'character_octet_length': 200, 'interval_type': None, 'dtd_identifier': '2', 'interval_precision': None, 'numeric_scale': None, 'is_updatable': True, 'datetime_precision': None, 'ordinal_position': 2, 'column_default': None, 'numeric_precision_radix': None}
True

Insert data¶

You can insert data into a specific table by sending a request to its /rows subresource. The query part of the sent data contians the row you want to insert in form of a JSON-dictionary::

{
    'name_of_column_1': 'value_in_column_1',
    'name_of_column_2': 'value_in_column_2',
    ...
}

If you the row you want to insert should have a specific id, send a PUT-request to the /rows/{id}/ subresource. In case the id should be generated automatically, just ommit the id field in the data dictionary and send a POST-request to the /rows/new subresource. If successful, the response will contain the id of the new row.

In the following example, we want to add a row containing just the name “John Doe”, but we do not want to set the the id of this entry.

curl:

curl
    -X POST
    -H "Content-Type: application/json"
    -H 'Authorization: Token <your-token>'
    -d '{"query": {"name": "John Doe"}}'
    oep.iks.cs.ovgu.de/api/v0/schema/sandbox/tables/example_table/rows/

python:

>>> import requests
>>> data = {"query": {"name": "John Doe"}}
>>> result = requests.post(oep_url+'/api/v0/schema/sandbox/tables/example_table/rows/new', json=data, headers={'Authorization': 'Token %s'%your_token} )
>>> result.status_code
201
>>> json_result = result.json()
>>> json_result['data'] # Show the id of the new row
[[1]]

Alternatively, we can specify that the new row should be stored under id 12:

python:

>>> import requests
>>> data = {"query": {"name": "Mary Doe XII"}}
>>> result = requests.put(oep_url+'/api/v0/schema/sandbox/tables/example_table/rows/12', json=data, headers={'Authorization': 'Token %s'%your_token} )
>>> result.status_code
201

Our database should have the following structure now:

id: int	name: varchar(50)	geom: geometry(Point)
1	John Doe	NULL
12	Mary Doe XII	NULL

Select data¶

You can insert data into a specific table by sending a GET-request to its /rows subresource. No authorization is required to do so.

curl:

curl
    -X GET
    oep.iks.cs.ovgu.de/api/v0/schema/sandbox/tables/example_table/rows/

The data will be returned as list of JSON-dictionaries similar to the ones used when adding new rows:

[
    {
        "name": "John Doe",
        "geom": null,
        "id": 1
    }
]

python:

>>> result = requests.get(oep_url+'/api/v0/schema/sandbox/tables/example_table/rows/', )
>>> result.status_code
200
>>> json_result = result.json()
>>> json_result ==  [{'id': 1, 'name': 'John Doe', 'geom': None}, {'id': 12, 'name': 'Mary Doe XII', 'geom': None}]
True

There are also optional parameters for these GET-queries:

limit: Limit the number of returned rows
offset: Ignore the specified amount of rows
orderby: Name of a column to refer when ordering
column: Name of a column to include in the results. If not present, all

columns are returned
where: Constraint fourmulated as VALUE+OPERATOR+VALUE with
- VALUE: Constant or name of a column
- OPERATOR: One of the following:
  EQUALS or =,
  
  GREATER or >,
  
  LOWER or <,
  
  NOTEQUAL or != or <>,
  
  NOTGREATER or <=,
  
  NOTLOWER or >=,

>>> result = requests.get(oep_url+"/api/v0/schema/sandbox/tables/example_table/rows/?where=name=John+Doe", )
>>> result.status_code
200
>>> json_result = result.json()
>>> json_result == [{'id': 1, 'name': 'John Doe', 'geom': None}]
True

>>> result = requests.get(oep_url+"/api/v0/schema/sandbox/tables/example_table/rows/1", )
>>> result.status_code
200
>>> json_result = result.json()
>>> json_result == {'id': 1, 'name': 'John Doe', 'geom': None}
True

>>> result = requests.get(oep_url+"/api/v0/schema/sandbox/tables/example_table/rows/?offset=1")
>>> result.status_code
200
>>> json_result = result.json()
>>> json_result == [{'id': 12, 'name': 'Mary Doe XII', 'geom': None}]
True

>>> result = requests.get(oep_url+"/api/v0/schema/sandbox/tables/example_table/rows/?column=name&column=id")
>>> result.status_code
200
>>> json_result = result.json()
>>> json_result == [{'id': 1, 'name': 'John Doe'},{'id': 12, 'name': 'Mary Doe XII'}]
True

Add columns table¶

>>> data = {'query':{'data_type': 'varchar', 'character_maximum_length': 30}}
>>> result = requests.put(oep_url+"/api/v0/schema/sandbox/tables/example_table/columns/first_name", json=data, headers={'Authorization': 'Token %s'%your_token})
>>> result.status_code
201

>>> result = requests.get(oep_url+"/api/v0/schema/sandbox/tables/example_table/columns/first_name")
>>> result.status_code
200
>>> result.json() == {'numeric_scale': None, 'numeric_precision_radix': None, 'is_updatable': True, 'maximum_cardinality': None, 'character_maximum_length': 30, 'character_octet_length': 120, 'ordinal_position': 4, 'is_nullable': True, 'interval_type': None, 'data_type': 'character varying', 'dtd_identifier': '4', 'column_default': None, 'datetime_precision': None, 'interval_precision': None, 'numeric_precision': None}
True

Alter data¶

Our current table looks as follows:

id: int	name: varchar(50)	geom: geometry(Point)	first_name: varchar(30)
1	John Doe	NULL	NULL
12	Mary Doe XII	NULL	NULL

Our next task is to distribute for and last name to the different columns:

>>> result = requests.get(oep_url+'/api/v0/schema/sandbox/tables/example_table/rows/') # Load the names via GET
>>> result.status_code
200
>>> for row in result.json():
...     first_name, last_name = str(row['name']).split(' ', 1) # Split the names at the first space
...     data = {'query': {'name': last_name, 'first_name': first_name}} # Build the data dictionary and post it to /rows/<id>
...     result = requests.post(oep_url+'/api/v0/schema/sandbox/tables/example_table/rows/{id}'.format(id=row['id']), json=data, headers={'Authorization': 'Token %s'%your_token})
...     result.status_code
200
200

Now, our table looks as follows:

id: int	name: varchar(50)	geom: geometry(Point)	first_name: varchar(30)
1	Doe	NULL	John
12	Doe XII	NULL	Mary

Alter tables¶

Currently, rows are allowed that contain no first name. In order to prohibit such behaviour, we have to set column first_name to NOT NULL. Such ALTER TABLE commands can be executed by POST-ing a dictionary with the corresponding values to the column’s resource:

>>> data = {'is_nullable': False}
>>> result = requests.post(oep_url+"/api/v0/schema/sandbox/tables/example_table/columns/first_name", json=data, headers={'Authorization': 'Token %s'%your_token} )
>>> result.status_code
200

We can check, whether your command worked by retrieving the corresponding resource:

>>> result = requests.get(oep_url+"/api/v0/schema/sandbox/tables/example_table/columns/first_name")
>>> result.status_code
200
>>> json_result = result.json()
>>> json_result['is_nullable']
False

After prohibiting null-values in the first name column, such rows can not be added anymore.

>>> import requests
>>> data = {"query": {"name": "McPaul"}}
>>> result = requests.post(oep_url+'/api/v0/schema/sandbox/tables/example_table/rows/new', json=data, headers={'Authorization': 'Token %s'%your_token} )
>>> result.status_code
500
>>> result.json()['reason']
'Action violates not-null constraint on first_name. Failing row was (McPaul)'

>>> import requests
>>> data = {"query": {"name": "McPaul"}}
>>> result = requests.delete(oep_url+'/api/v0/schema/sandbox/tables/example_table/rows/1', json=data, headers={'Authorization': 'Token %s'%your_token} )
>>> result.status_code
200

How to work with the API - An example¶

Authenticate¶

Create table¶

Insert data¶

Select data¶

Add columns table¶

Alter data¶

Alter tables¶

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