# 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)
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://prof-rossetti.gitbook.io/intro-to-python/notes/python/packages/sqlalchemy.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.