Backend example

This example showcases the BESSER backend generator’s capability to produce essential components for a backend service, based on the Library example B-UML model.

The generator creates three primary files, which together form the backbone of the backend system, here’s a snippet from the generated files:

main_api.py:Contains the REST API endpoints that define how the server responds to client requests:

 ############################################
 #   Initialize the database
 ############################################

 SQLALCHEMY_DATABASE_URL = "sqlite:///./Library model.db"
 engine = create_engine(
     SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
 )
 SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
 Base.metadata.create_all(bind=engine)

 app = FastAPI()

 # Initialize database session
 def get_db():
     database = SessionLocal()
     yield database
     database.close()
 ############################################
 #   Library functions
 ############################################

 @app.get("/book/", response_model=None)
def get_all_book(database: Session = Depends(get_db)) -> list[Book]:
  book_list = database.query(Book).all()
  return book_list

sql_alchemy.py: This file includes the SQLAlchemy ORM models that map Python classes to database tables:

class Book(Base):
 __tablename__ = "book"
 id: Mapped[int] = mapped_column(primary_key=True)
 pages: Mapped[int] = mapped_column(Integer)
 title: Mapped[str] = mapped_column(String(100))
 release: Mapped[datetime] = mapped_column(DateTime)


#--- Foreign keys and relationships of the library table
Library.has: Mapped[List["Book"]] = relationship("Book", back_populates="locatedIn")

pydantic_classes.py : Comprises Pydantic models for data validation and serialization:

class BookCreate(BaseModel):
  pages: int
  title: str
  release: datetime
  library_id: int
  authors: Optional[List[Union["AuthorCreate", int]]] = None

After launching the main_api.py file, the server will be up and running, and the client can interact with the backend service through the defined REST API endpoints. It will create a SQLite database according to the defined models in the sql_alchemy.py file.

After doing POST request to the endpoint, the database will be updated with the new book information:

Note

It is important to note that the generated code is a starting point and can be further customized to meet the specific requirements of the backend service.