Postgres database connection requires psycopg2 library which causes pickle error

[chimeracle]

Attempting to query from a Postgres database causes a psycopg2 missing error. After pip installing psycopg2 and then attempting to "reflex run", I get the error: TypeError: cannot pickle 'module' object. Uninstalling the psycopg2 library and attempting to run gives the error: ModuleNotFoundError: No module named 'psycopg2'. Am I missing something in my configuration? Do I need different versions of anything?

import reflex as rx
class Grades(rx.Model, table=True):
    username: str
    course: str
    grade: str
class State(rx.State):
    grades: list[Grades]
    with rx.session() as session:
        grades = session.query(Grades).filter(Grades.username == "test").all()
        print(grades)
def render_grade(grade):
    return rx.tr(
            rx.td(grade.course),
            rx.td(grade.grade),
    )
def index() -> rx.Component:
    return rx.fragment(
        rx.color_mode_button(rx.color_mode_icon(), float="right"),
        rx.vstack(
            rx.heading("Welcome to Reflex!", font_size="2em"),
            rx.box("Your grades."),
            rx.table(
                rx.thead(
                    rx.tr(
                        rx.th("Class"),
                        rx.th("Grade"),
                    )
                ),
                rx.tbody(
                    rx.foreach(State.grades, render_grade),
                ),
            ),
            spacing="1.5em",
            font_size="2em",
            padding_top="10%",
        ),
    )
app = rx.App()
app.add_page(index)
app.compile()

config

import reflex as rx

class ReflexappConfig(rx.Config):
    pass

config = ReflexappConfig(
    app_name="reflex_app3",
    db_url="postgresql://service_account:password1@localhost:5432/School"
)

Psycopg2 installed:

Traceback (most recent call last):
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "C:\Users\PycharmProjects\reflex_app3\venv\Scripts\reflex.exe\__main__.py", line 7, in <module>
    sys.exit(cli())
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\typer\main.py", line 214, in __call__
    return get_command(self)(*args, **kwargs)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\click\core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\click\core.py", line 1078, in main
    rv = self.invoke(ctx)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\click\core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\click\core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\click\core.py", line 783, in invoke
    return __callback(*args, **kwargs)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\typer\main.py", line 532, in wrapper
    return callback(**use_params)  # type: ignore
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\reflex\reflex.py", line 146, in run
    prerequisites.get_app()
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\reflex\utils\prerequisites.py", line 113, in get_app
    app = __import__(module, fromlist=(constants.APP_VAR,))
  File "C:\Users\PycharmProjects\reflex_app3\reflex_app3\reflex_app3.py", line 13, in <module>
    class State(rx.State):
  File "pydantic\main.py", line 221, in pydantic.main.ModelMetaclass.__new__
  File "pydantic\fields.py", line 506, in pydantic.fields.ModelField.infer
  File "pydantic\fields.py", line 436, in pydantic.fields.ModelField.__init__
  File "pydantic\fields.py", line 546, in pydantic.fields.ModelField.prepare
  File "pydantic\fields.py", line 570, in pydantic.fields.ModelField._set_default_and_type
  File "pydantic\fields.py", line 439, in pydantic.fields.ModelField.get_default
  File "pydantic\utils.py", line 693, in pydantic.utils.smart_deepcopy
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 270, in _reconstruct
    state = deepcopy(state, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 230, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 270, in _reconstruct
    state = deepcopy(state, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 230, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 270, in _reconstruct
    state = deepcopy(state, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 230, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 270, in _reconstruct
    state = deepcopy(state, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 230, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\copy.py", line 161, in deepcopy
    rv = reductor(4)
TypeError: cannot pickle 'module' object

Uninstalled psycopg2 error:

Traceback (most recent call last):
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Users\AppData\Local\Programs\Python\Python39\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "C:\Users\PycharmProjects\reflex_app3\venv\Scripts\reflex.exe\__main__.py", line 7, in <module>
    sys.exit(cli())
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\typer\main.py", line 214, in __call__
    return get_command(self)(*args, **kwargs)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\click\core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\click\core.py", line 1078, in main
    rv = self.invoke(ctx)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\click\core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\click\core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\click\core.py", line 783, in invoke
    return __callback(*args, **kwargs)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\typer\main.py", line 532, in wrapper
    return callback(**use_params)  # type: ignore
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\reflex\reflex.py", line 146, in run
    prerequisites.get_app()
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\reflex\utils\prerequisites.py", line 113, in get_app
    app = __import__(module, fromlist=(constants.APP_VAR,))
  File "C:\Users\PycharmProjects\reflex_app3\reflex_app3\reflex_app3.py", line 12, in <module>
    class State(rx.State):
  File "C:\Users\PycharmProjects\reflex_app3\reflex_app3\reflex_app3.py", line 14, in State
    with rx.session() as session:
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\reflex\model.py", line 291, in session
    return sqlmodel.Session(get_engine(url))
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\reflex\model.py", line 50, in get_engine
    return sqlmodel.create_engine(url, echo=echo_db_query, connect_args=connect_args)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\sqlmodel\engine\create.py", line 139, in create_engine
    return _create_engine(url, **current_kwargs)  # type: ignore
  File "<string>", line 2, in create_engine
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\sqlalchemy\util\deprecations.py", line 309, in warned
    return fn(*args, **kwargs)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\sqlalchemy\engine\create.py", line 548, in create_engine
    dbapi = dialect_cls.dbapi(**dbapi_args)
  File "C:\Users\PycharmProjects\reflex_app3\venv\lib\site-packages\sqlalchemy\dialects\postgresql\psycopg2.py", line 811, in dbapi
    import psycopg2
ModuleNotFoundError: No module named 'psycopg2'

[martinxu9]

Hi @chimeracle,

psycopg2 is needed. Reflex uses sqlmodel/sqlalchemy to connect to DB, and the default postgres driver is that. I was able to repro your error. This piece of code below caused the error. The with db query lines, instead of spilled out, should've been inside a handler , maybe a computed var with @rx.var decorator? Having said that, I suppose we do need to throw a better error message for the problem.

class State(rx.State):
    grades: list[Grades]
    with rx.session() as session:
        grades = session.query(Grades).filter(Grades.username == "test").all()
        print(grades)

Hope that helps.

[chimeracle]

Hey @martinxu9 ,
Thanks for the guidance. I changed the State to the code below and added the onload event to the add_page. It ran!

For anyone else having this issue, here's the corrected code below. FYI: If you use get_grades(), it will throw a List not callable error.

import reflex as rx


class Grades(rx.Model, table=True):
    username: str
    course: str
    grade: str


class State(rx.State):
    grades: list[Grades]

    @rx.var
    def get_grades(self) -> list[Grades]:
        with rx.session() as session:
            grades = session.query(Grades).filter(Grades.username == "test").all()
            print(grades)
        return grades

    def onload(self):
        self.grades = self.get_grades


def render_grade(grade):
    return rx.tr(
            rx.td(grade.course),
            rx.td(grade.grade),
    )


def index() -> rx.Component:
    return rx.fragment(
        rx.color_mode_button(rx.color_mode_icon(), float="right"),
        rx.vstack(
            rx.heading("Welcome to Reflex!", font_size="2em"),

            rx.box("Your grades."),
            rx.table(
                rx.thead(
                    rx.tr(
                        rx.th("Class"),
                        rx.th("Grade"),
                    )
                ),
                rx.tbody(
                    rx.foreach(State.grades, render_grade),
                ),
            ),
            spacing="1.5em",
            font_size="2em",
            padding_top="10%",
        ),
    )


# Add state and page to the app.
app = rx.App()
app.add_page(index, on_load=State.onload)
app.compile()