Using `get_joined` and `get_multi_joined` for multiple models

Added

Now get_joined and get_multi_joined can be used with multiple models.

Detailed

To facilitate complex data relationships, get_joined and get_multi_joined can be configured to handle joins with multiple models. This is achieved using the joins_config parameter, where you can specify a list of JoinConfig instances, each representing a distinct join configuration.

Example: Joining User, Tier, and Department Models

Consider a scenario where you want to retrieve users along with their associated tier and department information. Here's how you can achieve this using get_multi_joined.

Start by creating a list of the multiple models to be joined:

from fastcrud import JoinConfig

joins_config = [
    JoinConfig(
        model=Tier,
        join_on=User.tier_id == Tier.id,
        join_prefix="tier_",
        schema_to_select=TierSchema,
        join_type="left",
    ),

    JoinConfig(
        model=Department,
        join_on=User.department_id == Department.id,
        join_prefix="dept_",
        schema_to_select=DepartmentSchema,
        join_type="inner",
    )
]

users = await user_crud.get_multi_joined(
    db=session,
    schema_to_select=UserSchema,
    joins_config=joins_config,
    offset=0,
    limit=10,
    sort_columns='username',
    sort_orders='asc'
)

Then just pass this list to joins_config:

from fastcrud import JoinConfig

joins_config = [
    ...
]

users = await user_crud.get_multi_joined(
    db=session,
    schema_to_select=UserSchema,
    joins_config=joins_config,
    offset=0,
    limit=10,
    sort_columns='username',
    sort_orders='asc'
)

In this example, users are joined with the Tier and Department models. The join_on parameter specifies the condition for the join, join_prefix assigns a prefix to columns from the joined models (to avoid naming conflicts), and join_type determines whether it's a left or inner join.

[!WARNING] If both single join parameters and joins_config are used simultaneously, an error will be raised.

igorbenav / fastcrud