![]() From the example, the books table has a foreign key field pointing to the id field of the authors table. Relationships between SQL tables are described in terms of foreign key relationships. LBooks = DBSession.query(Book).filter(or_(Book.price<20,promote=True)) # returns all books that cost less than 20 OR are being promotedĭBSession.query(Book).order_by(Book.price) #get all books ordered by priceĭBSession.query(Book).order_by(desc(Book.price)) #get all books ordered by price descendingĭBSession.query(Book).count() #returns the number of booksĭBSession.query(Book).offset(5) #offset the result by 5ĭBSession.query(Book).limit(5) # return at most 5 booksĭBSession.query(Book).first() #return the first book only or NoneĭBSession.query(Book).get(8) #return the Book with primary key = 8, or None #logical operations can be used in filters LBooks = DBSession.query(Book).filter_by(author_id=1).filter(Book.price<20) #all books by a specific author, with price<20 ![]() LBooks = DBSession.query(Book).filter(Book.price<20) #returns all the books with price <20. LBooks = DBSession.query(Book).filter_by(author_id=1) #returns all the books for a specific author LBooks = DBSession.query(Book) #returns a Query object. Selecting and Filtering #fetch everything Promote = Column(Boolean,default= False) # or as values Queries and Interactions Name = Column(String( 50)) # string column need lengthsĪuthor_id = Column(Integer,ForeignKey( 'authors.id')) # assumes there is a table in the database called 'authors' that has an 'id' columnĭate_added = Column(DateTime, default=) # defaults can be specified as functions Id = Column(Integer,Sequence( 'book_seq'),primary_key= True) # plays nice with all major database engines _tablename_ = "books" #matches the name of the actual database table ![]() For example: from import declarative_baseįrom sqlalchemy.orm import scoped_session,sessionmakerįrom zope.sqlalchemy import ZopeTransactionExtensionĭBSession = scoped_session(sessionmaker(extension=ZopeTransactionExtension()))Ĭlass Book (Base): #<. One model is used to describe one database table. That said, if you are familiar with SQL then this cheat sheet should get you well on your way to understanding SQLAlchemy. This cheat sheet sticks to parts of the ORM (Object Relational Mapper) layer,and aims to be a reference not a tutorial. SQLAlchemy is a deep and powerful thing made up of many layers. ![]()
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