> ## Documentation Index
> Fetch the complete documentation index at: https://docs.chainlit.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Custom Data Layer

The `BaseDataLayer` class serves as an abstract foundation for data persistence operations within the Chainlit framework.
This class outlines methods for managing users, feedback, elements, steps, and threads in a chatbot application.

## Methods

<ParamField path="async get_user(self, identifier: str)" type="Coroutine">
  Fetches a user by their identifier. Return type is optionally a `PersistedUser`.
</ParamField>

<ParamField path="async create_user(self, user: User)" type="Coroutine">
  Creates a new user based on the `User` instance provided. Return type is optionally a `PersistedUser`.
</ParamField>

<ParamField path="async upsert_feedback(self, feedback: Feedback)" type="Coroutine">
  Inserts or updates feedback. Accepts a `Feedback` instance and returns a string as an identifier of the persisted feedback.
</ParamField>

<ParamField path="async delete_feedback(self, feedback_id: str)" type="Coroutine">
  Deletes a feedback by `feedback_id`. Return `True` if it was successful.
</ParamField>

<ParamField path="async create_element(self, element_dict: ElementDict)" type="Coroutine" optional>
  Adds a new element to the data layer. Accepts `ElementDict` as an argument.
</ParamField>

<ParamField path="async get_element(self, thread_id: str, element_id: str)" type="Coroutine">
  Retrieves an element by `thread_id` and `element_id`. Return type is optionally an `ElementDict`.
</ParamField>

<ParamField path="async delete_element(self, element_id: str)" type="Coroutine" optional>
  Deletes an element given its identifier `element_id`.
</ParamField>

<ParamField path="async create_step(self, step_dict: StepDict)" type="Coroutine" optional>
  Creates a new step in the data layer. Accepts `StepDict` as an argument.
</ParamField>

<ParamField path="async update_step(self, step_dict: StepDict)" type="Coroutine" optional>
  Updates an existing step. Accepts `StepDict` as an argument.
</ParamField>

<ParamField path="async delete_step(self, step_id: str)" type="Coroutine" optional>
  Deletes a step given its identifier `step_id`.
</ParamField>

<ParamField path="async get_thread_author(self, thread_id: str)" type="Coroutine">
  Fetches the author of a given thread by `thread_id`. Returns a string representing the author identifier.
</ParamField>

<ParamField path="async delete_thread(self, thread_id: str)" type="Coroutine">
  Deletes a thread given its identifier `thread_id`.
</ParamField>

<ParamField path="async list_threads(self, pagination: Pagination, filters: ThreadFilter)" type="Coroutine">
  Lists threads based on `pagination` and `filters` arguments. Returns a `PaginatedResponse[ThreadDict]`.
</ParamField>

<ParamField path="async get_thread(self, thread_id: str)" type="Coroutine">
  Retrieves a thread by its identifier `thread_id`. Return type is optionally a `ThreadDict`.
</ParamField>

<ParamField path="async update_thread(self, thread_id: str, name: Optional[str] = None, user_id: Optional[str] = None, metadata: Optional[Dict] = None, tags: Optional[List[str]] = None)" type="Coroutine">
  Updates a thread's details like name, user\_id, metadata, and tags. Arguments are mostly optional.
</ParamField>

<ParamField path="async delete_user_session(self, id: str)" type="Coroutine">
  Deletes a user session given its identifier `id`. Returns a boolean value indicating success.
</ParamField>

<ParamField path="async get_favorite_steps(self, user_id: str)" type="Coroutine">
  Returns the list of steps that the user has marked as favorites. Used to populate the favorite messages (prompt templates) feature in the composer. Returns a `List[StepDict]`.

  <Note>
    Since version **2.9.5**.
  </Note>
</ParamField>

<ParamField path="async close(self)" type="Coroutine">
  Called when the Chainlit server shuts down. Use this to close database connections, HTTP sessions, or other resources held by the data layer. Must be implemented by all subclasses.

  <Warning>
    Since version **2.8.2**. This is a **breaking change** — all custom `BaseDataLayer` and `BaseStorageClient` subclasses must implement this method.
  </Warning>
</ParamField>

## Decorators

<ParamField path="queue_until_user_message()" type="Decorator">
  Queues certain methods to execute only after the first user message is received, especially useful for `WebsocketSessions`.
</ParamField>

## Example

Due to the abstract nature of `BaseDataLayer`, direct instantiation and usage are not practical without subclassing and implementing the abstract methods.

You can refer to the [guide for custom data layer implementation](/data-layers/overview).