Fabric User data functions programming model overview (Preview)

The Fabric User data functions programming model is an SDK that provides the necessary functionality to author and publish runnable functions in Fabric. The SDK also allows you to seamlessly integrate with other items in the Fabric ecosystem, such as Fabric data sources. This library is publicly available in PyPI and is pre-installed in your user data functions items.

User data functions SDK

A user data functions item contains one or many functions you can invoke from the Fabric portal, from another Fabric item, or from an external application using the provided REST endpoint. Each function is a method in your Python script that allows passing parameters and returning an output to the invoker. The User data functions programming model contains the following components:

• The fabric.functions library provides the code you need to create user data functions in Python. You can see this library being imported in your first function template when you create a new user data functions item.

• The method fn.UserDataFunctions() provides the execution context. It's added at the beginning of the code file in all new user data functions items, before any function definitions.

  Example:

  import datetime
  import fabric.functions as fn
  import logging
  
  udf = fn.UserDataFunctions()
  

• Every function is identified with a @udf.function() decorator. This decorator will define if your function can be invoked individually from the portal or an external invoker.

  Invokable function example

  # This is a hello fabric function sample that can be invoked from the Fabric portal, another Fabric item, or an external application.
  
  @udf.function()
  def hello_fabric(name: str) -> str:
      logging.info('Python UDF trigger function processed a request.')
      logging.info('Executing hello fabric function.')
  
      return f"Welcome to Fabric Functions, {name}, at {datetime.datetime.now()}!"
  

• Any Python methods without the @udf.function() decorator can't be invoked directly. They can only be invoked from functions that contain the decorator, and can be used as helper functions.

  Helper function example

  # This is a helper function that can be invoked from other functions, but can't be invoked or run directly because it doesn't have the @udf.function() decorator
  
  def uppercase_name(name: str) -> str:
      return name.upper()
  

Supported input types

You can define input parameters for the function such as primitive data types like str, int, float, etc. The supported input data types are:

Supported output types

The supported output data types are:

Data connections to Fabric data sources

This module allows you to reference the data connections without the need for writing connection strings in your code. The fabric.functions library provides two ways to handle data connections:

• fabric.functions.FabricSqlConnection: Allows you to work with SQL databases in Fabric, including SQL Analytics endpoints and Fabric warehouses.
• fabric.functions.FabricLakehouseClient: Lets you work with Lakehouses, with a way to connect to both Lakehouse tables and Lakehouse files.

To reference a connection to a data source, you need to use the @udf.connection decorator. You can apply it in any of the following formats:

• @udf.connection(alias="<alias for data connection>", argName="sqlDB")
• @udf.connection("<alias for data connection>", "<argName>")
• @udf.connection("<alias for data connection>")

The arguments for @udf.connection are:

• argName, the name of the variable the connection will use in your function.
• alias, the alias of the connection you added with the Manage connections menu.
• If argName and alias have the same value, you can use @udf.connection("<alias and argName for the data connection>").

Example

# Where demosqldatabase is the argument name and the alias for my data connection used for this function
@udf.connection("demosqldatabase")
@udf.function()
def read_from_sql_db(demosqldatabase: fn.FabricSqlConnection)-> list:
  # Replace with the query you want to run
  query = "SELECT * FROM (VALUES ('John Smith', 31), ('Kayla Jones', 33)) AS Employee(EmpName, DepID);"

  # [...] Here is where the rest of your SqlConnection code would be.

  return results

Get invocation properties using UserDataFunctionContext

The programming model also includes the UserDataFunctionContext object. This object contains the function invocation metadata and can be used to create specific app logic for certain invocation mechanisms.

The following table shows the properties for the UserDataFunctionContext object:

The ExecutingUser object contains the following information:

To access the UserDataFunctionContext parameter, you must use the following decorator at the top of the function definition: @udf.context(argName="<parameter name>")

Example

@udf.context(argName="myContext")
@udf.function()
def getContext(myContext: fabric.functions.UserDataFunctionContext)-> str:
    logging.info('Python UDF trigger function processed a request.')
    return f"Hello oid = {context.executing_user['Oid']}, TenantId = {context.executing_user['TenantId']}, PreferredUsername = {context.executing_user['PreferredUsername']}, InvocationId = {context.invocation_id}"

Throw a handled error with UserThrownError

When developing your function, you can throw an expected error response by using the UserThrownError method available in the Python programming model. One use of this method is managing cases where the user-provided inputs fail to pass business validation rules.

Example

import datetime

@udf.function()
def raise_userthrownerror(age: int)-> str:
    if age < 18:
        raise fn.UserThrownError("You must be 18 years or older to use this service.", {"age": age})

    return f"Welcome to Fabric Functions at {datetime.datetime.now()}!"

This UserThrownError method takes two parameters:

• Message: This string will be returned as the error message to the application that is invoking this function.
• A dictionary of properties that will be returned to the application that is invoking this function.

Next steps

• Create a Fabric User data functions item
• User data functions samples