Setup alembic to work properly with PostgreSQL schemas

env.py

from __future__ import with_statement
from alembic import context
from sqlalchemy import engine_from_config, pool
from logging.config import fileConfig

from models import Base

config = context.config

fileConfig(config.config_file_name)

"""
Load models metadata. We should define schema in this class firstly, 
or set schema implicit with `__table_args__ = {'schema' : 'test'}` in model class
"""
target_metadata = Base.metadata


def run_migrations_offline():
    url = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url, target_metadata=target_metadata, literal_binds=True)

    with context.begin_transaction():
        context.run_migrations()


def run_migrations_online():
    connectable = engine_from_config(
        config.get_section(config.config_ini_section),
        prefix='sqlalchemy.',
        poolclass=pool.NullPool)

    with connectable.connect() as connection:
        """
        Configure migration context
        1. Pass our models metadata
        2. Set schema for alembic_version table
        3. Load all available schemas
        """
        context.configure(
            connection=connection,
            target_metadata=target_metadata,
            version_table_schema=target_metadata.schema,
            include_schemas=True
        )

        with context.begin_transaction():
            """
            By default search_path is setted to "$user",public 
            that why alembic can't create foreign keys correctly
            """
            context.execute('SET search_path TO public')
            context.run_migrations()


if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()

After spending a lot of time struggling to get my alembic to work, with a schema_name other than "public", I've come up with the following solution:
[The only solution that worked for me on February 16, 2024]

def run_migrations_online() -> None:
    """Run migrations in 'online' mode.

    In this scenario we need to create an Engine
    and associate a connection with the context.

    """
    connectable = engine_from_config(
        config.get_section(config.config_ini_section, {}),
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )

    with connectable.connect() as connection:
        context.configure(connection=connection, target_metadata=target_metadata)

        connection.execute(text('set search_path to "%s"' % settings.postgres_db_schema)) #  <-- The magic line

        with context.begin_transaction():
            context.run_migrations()

Hope this helps