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User-Defined Functions
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This tutorial shows how to add user-defined functions (UDF) to PGX and how to use them in PGQL and Green-Marl.
The examples will focus on Java and JavaScript UDFs.

Using UDFs in PGX
-----------------

After configuring the UDFs, they can now be used in PGX and the next two sections will show how they can be utilized in `PGQL` and `Green-Marl` (not available in all releases).

First we start PGX in local mode:

.. code-block:: python
    :linenos:

    session = pypgx.get_session(session_name="my-session")

Next, let us load a graph into memory that we can use in the subsequent examples.

.. code-block:: python
    :linenos:

    connections_graph = session.read_graph_with_properties(
        "examples/graphs/connections.csv.json"
    )

UDFs in PGQL
~~~~~~~~~~~~

PGQL can call UDFs directly using the ``namespace`` and ``function_name``.
Note that the namespace is required, otherwise the function will be interpreted as a built-in function.
UDFs can be used in any part of the PGQL query, e.g. the following query utilizes them in the `SELECT` clause.

.. code-block:: python
    :linenos:

    result_set = connections_graph.query_pgql(
        """
        SELECT 
            DISTINCT udfTutorial.format(v.name, v.country), 
            udfTutorial.toHexString(e.weight) 
        FROM MATCH (v) -[e]-> (u)
        """
    )