Add default ordering, new aggr functions, new signals

0.9.9

Features

• Add possibility to change default ordering of relations and models.
  • To change model sorting pass orders_by = [columns] where columns: List[str] to model Meta class
  • To change relation order_by pass orders_by = [columns] where columns: List[str]
  • To change reverse relation order_by pass related_orders_by = [columns] where columns: List[str]
  • Arguments can be column names or -{col_name} to sort descending
  • In relations you can sort only by directly related model columns
    or for ManyToMany columns also Through model columns "{through_field_name}__{column_name}"
  • Order in which order_by clauses are applied is as follows:
    • Explicitly passed order_by() calls in query
    • Relation passed orders_by if exists
    • Model Meta class orders_by
    • Model primary key column asc (fallback, used if none of above provided)
• Add 4 new aggregated functions -> min, max, sum and avg that are their
  corresponding sql equivalents.
  • You can pass one or many column names including related columns.
  • As of now each column passed is aggregated separately (so sum(col1+col2) is not possible,
    you can have sum(col1, col2) and later add 2 returned sums in python)
  • You cannot sum and avg non numeric columns
  • If you aggregate on one column, the single value is directly returned as a result
  • If you aggregate on multiple columns a dictionary with column: result pairs is returned
• Add 4 new signals -> pre_relation_add, post_relation_add, pre_relation_remove and post_relation_remove
  • The newly added signals are emitted for ManyToMany relations (both sides)
    and reverse side of ForeignKey relation (same as QuerysetProxy is exposed).
  • Signals recieve following args: sender: Type[Model] - sender class,
    instance: Model - instance to which related model is added, child: Model - model being added,
    relation_name: str - name of the relation to which child is added,
    for add signals also passed_kwargs: Dict - dict of kwargs passed to add()

Changes

• Through models for ManyToMany relations are now instantiated on creation, deletion and update, so you can provide not only
  autoincrement int as a primary key but any column type with default function provided.
• Since Through models are now instantiated you can also subscribe to Through model
  pre/post save/update/delete signals
• pre_update signals receivers now get also passed_args argument which is a
  dict of values passed to update function if any (else empty dict)

Fixes

• pre_update signal now is sent before the extraction of values so you can modify the passed
  instance in place and modified fields values will be reflected in database
• bulk_update now works correctly also with UUID primary key column type