Python Filterparams

Filterparams is a library for parsing URL paramters for filter purposes in a backend. It provides a syntax to map SQL-like queries on top of the query parameters and parses it into a python object.

This is a helper library for providing filter collection APIs. The primary use case for developing the library is to use it with a REST-API which uses the JSONAPI standard. Because of this the syntax is completely compatible with the standard and encapsulates everything in the filter query parameter.

Installation

The package is available on PyPi. You can install it through

pip install filterparams

The library was tested and should work with Python 2.7 and every Python 3 release. It was also tested to be compatible with pypy and pypy3.

Example

Given the URL (non URL escaped for better readability):

/users?filter[param][name][like][no_brand_name]=doe&filter[param][first_name]=doe%&filter[binding]=(!no_brand_name&first_name)&filter[order]=name&filter[order]=desc(first_name)

It can be parsed by the given function:

from urllib.parse import urlsplit, parse_qs
from filterparams import build_parser

url = urlsplit(
    '/users?filter[param][name][like][no_brand_name]=doe'
    '&filter[param][first_name]=doe%&filter[binding]='
    '(!no_brand_name%26first_name)&filter[order]=name'
    '&filter[order]=desc(first_name)'
)
params = parse_qs(url.query)

valid_filters = ['eq', 'like']
default_filter = 'eq'

parser = build_parser(
    valid_filters=valid_filters,
    default_filter=default_filter,
)

query = parser(params)

Would parse the data. You can access the parsed filters through .param_order and the orders through .orders. The param order in this specific case would be resolved to:

And(
    left=Parameter(
        name='name',
        alias='no_default_name',
        filter='like',
        value='doe%',
    ),
    right=Parameter(
        name='first_name',
        alias='first_name',
        filter='eq',
        value='doe',
    )
)

The orders would be:

[Order(name='name', direction='asc'), 
 Order(name='first_name', direction='desc')]

Syntax

All arguments must be prefixed by "filter". It is possible to query for specific data with filters, apply orders to the result and to combine filters through AND, NOT and OR bindings.

The syntax builds under the filter parameter a virtual object. The keys of the object are simulated through specifying [{key}] in the passed query parameter. Thus filter[param] would point to the param key in the filter object.

Filter specification

The solution supports to query data through the param subkey.

filter[param][{parameter_name}][{operation}][{alias}] = {to_query_value}

The operation and alias parameters may be omitted. If no alias is provided the given parameter name is used for it. If no operation is given, the default one is used (in the example this would be equal).

Example:

filter[param][phone_number][like]=001%

This would add a filter to all phone numbers which start with "001".

Filter binding

Per default all filters are combined through AND clauses. You can change that by specifying the filter[binding] argument.

This is where the aliases which you can define come into place. The binding provides means to combine filters with AND and OR. Also you are able to negate filters here.

The filters are addressed by their alias or name, if no alias is provided.

If you have a filter search_for_name, search_for_phone_number and search_for_account_number defined you can say search_for_name OR NOT search_for_number AND search_for_account_number by specifying the following filter:

filter[binding]=search_for_name|(!search_for_phone_number&search_for_account_number)

Even though the brackets are useless here, you can use them in more complex filters.

The following table summarizes the possible configuration options:

Type	Symbol	Example
AND	&	a&b
OR	|	a|b
NOT	!	!a
Bracket	()	(a|b)&c

Ordering

To specify a sort order of the results the filter[order] parameter may be used. The value can be specified multiple times. To add ordering you have to provide the name of the parameter which should be ordered, not its alias!

If you want to order by name, first_name and in reverse order balance you can do so by specifying the following query url parameters:

filter[order]=name&filter[order]=first_name&filter[order]=desc(balance)

As you can see the desc() definition can be used to indicate reverse ordering.

Filter definition

Not every backend does or should support all possible filter mechanisms. This is why the filters which should be accepted by the backend have to be added before processing the query parameters.

You can limit the allowed filters by building a parse through the filterparams.build_parser function. You can configure the allowed filters through the valid_filters definition. Additionally you have to add the default filter by using the second default_filter parameter.

from filterparams import build_parser

valid_filters = ['eq', 'like']
default_filter = 'eq'

parser = build_parser(
    valid_filters=valid_filters,
    default_filter=default_filter,
)

query = parser({})

If you don't want any validation you can use the parse function.

from filterparams import parse

query = parse({})

Notes

• There do no yet exist any public projects which use this library to provide transparent mapping to an underlying backend. I plan long-term to add another library which does use this package and provide a way to map it on sqlalchemy models. If you are planning to do this or use it for other data mapping please contact me and I'll add a reference to it in the README.
• The same as mentioned above is valid for client libraries, which generate the filter query structure in any language. Again, as soon as the API is stable I'll probably add a JavaScript library.
• Depending on your backend it might not make sense to support all features (ordering, parameter binding) of the language. You might still want to use it to parse your basic parameters though and ignore the rest.

License

The project is licensed under the MIT License.

Used Libraries

For evaluating the filter params ordering the funcparserlib (MIT license) module is used. Additionally the Werkzeug (BSD license) package is used for supporting dicts with multiple values in the same key.

Bindings

At the moment there does only exist a binding for mapping the filter language on top of SQLAlchemy's declarative models. Other ones will be added to the list if they become available:

• sqlalchemy-filterparams - Mapper for SQLAlchemy declarative models.

Other Languages

This is a list of projects implementing the same API for other languages. Currently this list only has one entry.

• Go - go-filterparams
• Ruby - filterparams
• JavaScript (Client) - filterparams