Using Aliases

[igorbenav]

Using aliases

Added

• Now get_joined and get_multi_joined can be used with aliases, making it possible to join the same model multiple times.

Detailed

---

In complex query scenarios, particularly when you need to join a table to itself or perform multiple joins on the same table for different purposes, aliasing becomes crucial. Aliasing allows you to refer to the same table in different contexts with unique identifiers, avoiding conflicts and ambiguity in your queries.

For both get_joined and get_multi_joined methods, when you need to join the same model multiple times, you can utilize the alias parameter within your JoinConfig to differentiate between the joins. This parameter expects an instance of AliasedClass, which can be created using the aliased function from SQLAlchemy (also in fastcrud for convenience).

Example: Joining the Same Model Multiple Times

Consider a task management application where tasks have both an owner and an assigned user, represented by the same UserModel. To fetch tasks with details of both users, we use aliases to join the UserModel twice, distinguishing between owners and assigned users.

Let's start by creating the aliases and passing them to the join configuration. Don't forget to use the alias for join_on:

from fastcrud import FastCRUD, JoinConfig, aliased

# Create aliases for UserModel to distinguish between the owner and the assigned user
owner_alias = aliased(UserModel, name="owner")
assigned_user_alias = aliased(UserModel, name="assigned_user")

# Configure joins with aliases
joins_config = [
    JoinConfig(
        model=UserModel,
        join_on=Task.owner_id == owner_alias.id,
        join_prefix="owner_",
        schema_to_select=UserSchema,
        join_type="inner",
        alias=owner_alias  # Pass the aliased class instance
    ),
    JoinConfig(
        model=UserModel,
        join_on=Task.assigned_user_id == assigned_user_alias.id,
        join_prefix="assigned_",
        schema_to_select=UserSchema,
        join_type="inner",
        alias=assigned_user_alias  # Pass the aliased class instance
    )
]

# Initialize your FastCRUD instance for TaskModel
task_crud = FastCRUD(TaskModel)

# Fetch tasks with joined user details
tasks = await task_crud.get_multi_joined(
    db=session,
    schema_to_select=TaskSchema,
    joins_config=joins_config,
    offset=0,
    limit=10
)

Then just pass this joins_config to get_multi_joined:

from fastcrud import FastCRUD, JoinConfig, aliased

...

# Configure joins with aliases
joins_config = [
    ...
]

# Initialize your FastCRUD instance for TaskModel
task_crud = FastCRUD(TaskModel)

# Fetch tasks with joined user details
tasks = await task_crud.get_multi_joined(
    db=session,
    schema_to_select=TaskSchema,
    joins_config=joins_config,
    offset=0,
    limit=10
)

In this example, owner_alias and assigned_user_alias are created from UserModel to distinguish between the task's owner and the assigned user within the task management system. By using aliases, you can join the same model multiple times for different purposes in your queries, enhancing expressiveness and eliminating ambiguity.

Closes #27