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BackAnt uses SQLAlchemy with PostgreSQL via psycopg2. The database layer is configured in api/startup/Alchemy.py and accessed through the DBSession wrapper in api/helper/DBSession.py.

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How it works

On application startup, create_app() in app.py calls init_db(): 
from startup.Alchemy import init_db
init_db()
init_db() imports all models (so SQLAlchemy knows about all tables), optionally drops them if CLEAR_DB=True, then creates any missing tables: 
def init_db():
    import models.Default_model
    # all generated models are imported here by `ant generate route`

    if myEnvironment.CLEAR_DB == "True":
        Base.metadata.drop_all(engine)
    try:
        Base.metadata.create_all(engine)
    except Exception as e:
        myLogger.warning(f"Could not connect to DB because of <{e}>")
        quit(1)

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Engine and session

The engine connects to PostgreSQL using credentials from Environment.py: 
engine = create_engine(
    f"postgresql+psycopg2://{db_user}:{db_password}@{db_url}/{db}"
)

db_session = scoped_session(
    sessionmaker(autocommit=False, autoflush=False, bind=engine)
)

Base = declarative_base()
db_session is a thread-local scoped session. It is removed at the end of each request via the teardown_appcontext hook in app.py.

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DBSession wrapper

All database operations go through the DBSession class in api/helper/DBSession.py. It wraps the scoped session with error handling and automatic rollback: 
from helper.DBSession import myDB

# In a repository:
stmt = select(Users)
results = myDB.execute(stmt).scalars().all()
The myDB singleton is pre-instantiated and injected into every repository.

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Adding a new model

When ant generate route <name> runs, it:
  1. Creates api/models/<Name>_model.py
  2. Adds an import of the model to init_db() in api/startup/Alchemy.py
The model is then included in create_all() on the next startup. No manual migration step is required for new tables in development.

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Environment variables

VariableDescription
POSTGRES_USERDatabase username
POSTGRES_PASSWORDDatabase password
POSTGRES_DBDatabase name
DB_URLHost — postgres inside Docker, localhost for local dev
CLEAR_DBSet to True to drop and recreate all tables on startup

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Connecting outside Docker

Set DB_URL=localhost in .env and ensure PostgreSQL is running locally on port 5432.