Sqlalchemy-filterset

Key Updates

1. Renaming of Strategies for Clarity:
- RelationJoinStrategy has been renamed to JoinStrategy
- RelationSubqueryExistsStrategy has been renamed to SubqueryExistsStrategy.

2. Enhanced JoinStrategy:
- JoinStrategy now supports additional attributes:
- is_outer: Enables the creation of outer joins.
- is_full: Enables the creation of full joins.

3. Introduction of MultiJoinStrategy:
- The new MultiJoinStrategy allows for the addition of several joins or several chained joins with filtering capabilities.
- This strategy is designed to handle complex querying scenarios where multiple joins and filters are required.

Example Usage

ParentsTagFilter
This filter demonstrates how to implement a custom filter using the new MultiJoinStrategy:

python
class ParentsTagFilter(Filter):
def filter(self, query, value, values):
expression = or_(Parent.name == value, GrandParent.name == value))
return self.strategy.filter(query, expression)

ItemFilterSet
This filter set showcases how to use the new MultiJoinStrategy in combination with JoinStrategy:

python
class ItemFilterSet(AsyncFilterSet[Item]):
several_joins = MultiJoinStrategy(
JoinStrategy(Parent, Item.parent_id == Parent.right_id),
JoinStrategy(GrandParent, Parent.grand_parent_id == GrandParent.id)
)

id = Filter(Item.id)
ids = InFilter(Item.id)
tag = ParentsTagFilter(strategy=several_joins)

With this update, all joins, whether originating from the base query or added via the RelationJoinStrategy, will be automatically deduplicated.

Suppose you have the following strategy defined:
`strategy = RelationJoinStrategy(Parent, onclause=Parent.id == Item.parent_id)`

Below are three different ways to construct a query:
1. `strategy.filter(select(Item.id), Parent.name == "test")`
2. `strategy.filter(select(Item.id).join(Parent), Parent.name == "test")`
3. `strategy.filter(select(Item.id).join(Parent, onclause=Parent.id == Item.parent_id), Parent.name == "test")`

With the new join deduplication feature, all of these methods will produce the same optimized query:

SELECT item.id
FROM item
JOIN parent ON parent.id = item.parent_id
WHERE parent.name = 'test'

1. Added IsNullFilter
2. Minor improvement: BaseFilterSet added to main __init__.py

Simplify imports and dependencies.