SQLAlchemy-filters
==================

.. pull-quote::

    Filter, sort and paginate SQLAlchemy query objects.
    Ideal for exposing these actions over a REST API.

Filtering
---------

Assuming that we have a SQLAlchemy `query` object:

.. code-block:: python

    from sqlalchemy import Column, Integer, String
    from sqlalchemy.ext.declarative import declarative_base


    class Base(object):
        id = Column(Integer, primary_key=True)
        name = Column(String(50), nullable=False)
        count = Column(Integer, nullable=True)


    Base = declarative_base(cls=Base)


    class Foo(Base):

        __tablename__ = 'foo'

    # ...

    query = session.query(Foo)

Then we can apply filters to that ``query`` object (multiple times):

.. code-block:: python

    from sqlalchemy_filters import apply_filters

    # `query` should be a SQLAlchemy query object

    filter_spec = [{'field': 'name', 'op': '==', 'value': 'name_1'}]
    filtered_query = apply_filters(query, filter_spec)

    more_filters = [{'field': 'foo_id', 'op': 'is_not_null'}]
    filtered_query = apply_filters(filtered_query, more_filters)

    result = filtered_query.all()

It is also possible to filter queries that contain multiple models, including joins:

.. code-block:: python

    class Bar(Base):

        __tablename__ = 'bar'
        foo_id = Column(Integer, ForeignKey('foo.id'))


.. code-block:: python

    query = session.query(Foo).join(Bar)

    filter_spec = [
        {'model': 'Foo', field': 'name', 'op': '==', 'value': 'name_1'},
        {'model': 'Bar', field': 'count', 'op': '>=', 'value': 5},
    ]
    filtered_query = apply_filters(query, filter_spec)

    result = filtered_query.all()


`apply_filters` will attempt to automatically join models to `query` if they're not already present and a model-specific filter is supplied. For example, the value of `filtered_query` in the following two code blocks is identical:

.. code-block:: python

    query = session.query(Foo).join(Bar)  # join pre-applied to query

    filter_spec = [
        {'model': 'Foo', field': 'name', 'op': '==', 'value': 'name_1'},
        {'model': 'Bar', field': 'count', 'op': '>=', 'value': 5},
    ]
    filtered_query = apply_filters(query, filter_spec)

.. code-block:: python

    query = session.query(Foo)  # join to Bar will be automatically applied

    filter_spec = [
        {field': 'name', 'op': '==', 'value': 'name_1'},
        {'model': 'Bar', field': 'count', 'op': '>=', 'value': 5},
    ]
    filtered_query = apply_filters(query, filter_spec)

The automatic join is only possible if sqlalchemy can implictly determine the condition for the join, for example because of a foreign key relationship.

Automatic joins allow flexibility for clients to filter and sort by related objects without specifying all possible joins on the server beforehand.

Note that first filter of the second block does not specify a model. It is implictly applied to the `Foo` model because that is the only model in the original query passed to `apply_filters`.

It is also possible to apply filters to queries defined by fields or functions:

.. code-block:: python

    query_alt_1 = session.query(Foo.id, Foo.name)
    query_alt_2 = session.query(func.count(Foo.id))


Restricted Loads
----------------

You can restrict the fields that SQLAlchemy loads from the database by using
the `apply_loads` function:

.. code-block:: python

    query = session.query(Foo, Bar).join(Bar)
    load_spec = [
        {'model': 'Foo', 'fields': ['name']},
        {'model': 'Bar', 'fields': ['count']}
    ]
    query = apply_loads(query, load_spec)  # will load only Foo.name and Bar.count


The effect of the `apply_loads` function is to _defer_ the load of any other fields to when/if they're accessed, rather than loading them when the query is executed. It only applies to fields that would be loaded during normal query execution.


Effect on joined queries
^^^^^^^^^^^^^^^^^^^^^^^^

The default SQLAlchemy join is lazy, meaning that columns from the joined table are loaded only when required. Therefore `apply_loads` has limited effect in the following scenario:

.. code-block:: python

    query = session.query(Foo).join(Bar)
    load_spec = [
        {'model': 'Foo', 'fields': ['name']}
        {'model': 'Bar', 'fields': ['count']}  # ignored
    ]
    query = apply_loads(query, load_spec)  # will load only Foo.name


`apply_loads` cannot be applied to columns that are loaded as `joined eager loads <http://docs.sqlalchemy.org/en/latest/orm/loading_relationships.html#joined-eager-loading>`_. This is because a joined eager load does not add the joined model to the original query, as explained `here <http://docs.sqlalchemy.org/en/latest/orm/loading_relationships.html#the-zen-of-joined-eager-loading>`_

The following would not prevent all columns from Bar being eagerly loaded:

.. code-block:: python

    query = session.query(Foo).options(joinedload(Foo.bar))
    load_spec = [
        {'model': 'Foo', 'fields': ['name']}
        {'model': 'Bar', 'fields': ['count']}
    ]
    query = apply_loads(query, load_spec)

.. sidebar:: Automatic Join

    In fact, what happens here is that `Bar` is automatically joined to `query`, because it is determined that `Bar` is not part of the original query. The `load_spec` therefore has no effect because the automatic join
    results in lazy evaluation.

If you wish to perform a joined load with restricted columns, you must specify the columns as part of the joined load, rather than with `apply_loads`:

.. code-block:: python

    query = session.query(Foo).options(joinedload(Bar).load_only('count'))
    load_spec = [
        {'model': 'Foo', 'fields': ['name']}
    ]
    query = apply_loads(query. load_spec)  # will load ony Foo.name and Bar.count


Sort
----

.. code-block:: python

    from sqlalchemy_filters import apply_sort

    # `query` should be a SQLAlchemy query object

    sort_spec = [
        {'model': 'Foo', field': 'name', 'direction': 'asc'},
        {'model': 'Bar', field': 'id', 'direction': 'desc'},
    ]
    sorted_query = apply_sort(query, sort_spec)

    result = sorted_query.all()


`apply_sort` will attempt to automatically join models to `query` if they're not already present and a model-specific sort is supplied. The behaviour is the same as in `apply_filters`.

This allows flexibility for clients to sort by fields on related objects without specifying all possible joins on the server beforehand.


Pagination
----------

.. code-block:: python

    from sqlalchemy_filters import apply_pagination

    # `query` should be a SQLAlchemy query object

    query, pagination = apply_pagination(query, page_number=1, page_size=10)

    page_size, page_number, num_pages, total_results = pagination

    assert 10 == len(query)
    assert 10 == page_size == pagination.page_size
    assert 1 == page_number == pagination.page_number
    assert 3 == num_pages == pagination.num_pages
    assert 22 == total_results == pagination.total_results

Filters format
--------------

Filters must be provided in a list and will be applied sequentially.
Each filter will be a dictionary element in that list, using the
following format:

.. code-block:: python

    filter_spec = [
        {'model': 'model_name', 'field': 'field_name', 'op': '==', 'value': 'field_value'},
        {'model': 'model_name', 'field': 'field_2_name', 'op': '!=', 'value': 'field_2_value'},
        # ...
    ]

The `model` key is optional if the original query being filtered only applies to one model.

If there is only one filter, the containing list may be omitted:

.. code-block:: python

    filter_spec = {'field': 'field_name', 'op': '==', 'value': 'field_value'}

Where ``field`` is the name of the field that will be filtered using the
operator provided in ``op`` (optional, defaults to `==`) and the
provided ``value`` (optional, depending on the operator).

This is the list of operators that can be used:

- ``is_null``
- ``is_not_null``
- ``==``, ``eq``
- ``!=``, ``ne``
- ``>``, ``gt``
- ``<``, ``lt``
- ``>=``, ``ge``
- ``<=``, ``le``
- ``like``
- ``ilike``
- ``in``
- ``not_in``

Boolean Functions
*****************
``and``, ``or``, and ``not`` functions can be used and nested within the filter specification:

.. code-block:: python

    filter_spec = [
        {
            'or': [
                {
                    'and': [
                        {'field': 'field_name', 'op': '==', 'value': 'field_value'},
                        {'field': 'field_2_name', 'op': '!=', 'value': 'field_2_value'},
                    ]
                },
                {
                    'not': [
                        {'field': 'field_3_name', 'op': '==', 'value': 'field_3_value'}
                    ]
                },
            ],
        }
    ]


Note: ``or`` and ``and`` must reference a list of at least one element. ``not`` must reference a list of exactly one element.

Sort format
-----------

Sort elements must be provided as dictionaries in a list and will be
applied sequentially:

.. code-block:: python

    sort_spec = [
        {'model': 'Foo', 'field': 'name', 'direction': 'asc'},
        {'model': 'Bar', 'field': 'id', 'direction': 'desc'},
        # ...
    ]

Where ``field`` is the name of the field that will be sorted using the
provided ``direction``.

The `model` key is optional if the original query being sorted only applies to one model.


Running tests
-------------

There are some Makefile targets that can be used to run the tests. A
test database will be created, used during the tests and destroyed
afterwards.

The default configuration uses both SQLite and MySQL (if the driver is
installed) to run the tests, with the following URIs:

.. code-block:: shell

    sqlite+pysqlite:///test_sqlalchemy_filters.db
    mysql+mysqlconnector://root:@localhost:3306/test_sqlalchemy_filters

Example of usage:

.. code-block:: shell

    $ # using default settings
    $ make test
    $ make coverage

    $ # overriding DB parameters
    $ ARGS='--mysql-test-db-uri mysql+mysqlconnector://root:@192.168.99.100:3340/test_sqlalchemy_filters' make test
    $ ARGS='--sqlite-test-db-uri sqlite+pysqlite:///test_sqlalchemy_filters.db' make test

    $ ARGS='--mysql-test-db-uri mysql+mysqlconnector://root:@192.168.99.100:3340/test_sqlalchemy_filters' make coverage
    $ ARGS='--sqlite-test-db-uri sqlite+pysqlite:///test_sqlalchemy_filters.db' make coverage


License
-------

Apache 2.0. See LICENSE for details.