Access variable library in UDF

Hi bruinsmm, 

In Fabric, a UDF can read a Variable Library only after you both create a Manage connections entry that points at the Variable Library item and reference that connection’s alias in your @udf.connection(...) decorator. If you skip step 1, the Variable Library won’t appear in the UDF’s connection picker.

1. Create the Variable Library item
   Workspace > New > Variable library > add variables (e.g., ENV, DEV_FILE_PATH, PROD_FILE_PATH).
   Docs: Variable Library overview
2. Create a workspace connection to that Variable Library
   Workspace header > Manage connections > New connection > Fabric item > Variable library > pick your VL item > note the Alias
   Docs: Connect to data sources for UDFs
3. Reference the alias in your UDF code and use the correct type

import fabric.functions as fn
from fabric.functions import udf

@udf.connection(argName="varLib", alias="MyVarLib")
@udf.function()
def get_storage_path(dataset: str, varLib: fn.FabricVariablesClient) -> str:
    variables = varLib.getVariables()
    env = (variables.get("ENV") or "").lower()
    dev_path  = variables.get("DEV_FILE_PATH") or ""
    prod_path = variables.get("PROD_FILE_PATH") or ""

    if env == "dev":
        return f"{dev_path}{dataset}/"
    elif env == "prod":
        return f"{prod_path}{dataset}/"
    else:
        return "incorrect settings defined for ENV variable"​

4. Publish the UDF, then open the UDF item and check the Connections pane. You should now see the Variable Library bound via the alias.

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