> For the complete documentation index, see [llms.txt](https://prof-rossetti.gitbook.io/intro-to-python/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://prof-rossetti.gitbook.io/intro-to-python/notes/python/packages/sqlalchemy.md).

# The sqlalchemy Package

Reference:

* <https://docs.sqlalchemy.org/en/13/>
* <https://docs.sqlalchemy.org/en/13/intro.html>
* <https://docs.sqlalchemy.org/en/13/dialects/postgresql.html#module-sqlalchemy.dialects.postgresql.psycopg2>
* <https://docs.sqlalchemy.org/en/13/core/type_basics.html>
* <https://docs.sqlalchemy.org/en/13/core/metadata.html#creating-and-dropping-database-tables>
* <https://docs.sqlalchemy.org/en/13/orm/extensions/declarative/api.html>
* <https://stackoverflow.com/questions/45259764/how-to-create-a-single-table-using-sqlalchemy-declarative-base>
* <https://www.compose.com/articles/using-postgresql-through-sqlalchemy/>
* <https://www.learndatasci.com/tutorials/using-databases-python-postgres-sqlalchemy-and-alembic/>

## Installation

```bash
pip install sqlalchemy
```

## Usage

```python
# models.py

import os
from dotenv import load_dotenv
from sqlalchemy import create_engine, Column, Integer, BigInteger, String, ARRAY, TIMESTAMP
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from sqlalchemy.orm.exc import NoResultFound

load_dotenv()

DATABASE_URL = os.getenv("DATABASE_URL", default="postgresql://username:password@localhost/dbname")

db = create_engine(DATABASE_URL)
Base = declarative_base()
Base.metadata.bind = db # fixes sqlalchemy.exc.UnboundExecutionError: Table object 'books' is not bound to an Engine or Connection.  Execution can not proceed without a database to execute against.
BoundSession = sessionmaker(bind=db)

class Book(Base):
    __tablename__ = "books"

    id = Column(Integer, primary_key=True)
    title = Column(String(128))
    author = Column(String(128))
    readers = Column(ARRAY(String(128)))


if __name__ == "__main__":

    #Book.__table__.drop(db)
    #Book.__table__.create(db)
    #if not Book.__table__.exists(): Book.__table__.create(db)
    Base.metadata.create_all(db)

    session = BoundSession()

    try:
        book = session.query(Book).filter(Book.title=="Harry Potter").one()
    except NoResultFound as err:
        book = Book(title="Harry Potter", author="JKR", readers=["John", "Jane", "Sally"])
        session.add(book)
        session.commit()

    print("-------")
    print("BOOKS:")
    books = session.query(Book)
    for book in books:
        print("...", book.id, "|", book.title, "|", book.author, "|", book.readers)
```