sqlalchemy existing db file 1

sqlalchemy existing db file

from sqlalchemy.ext.automap import automap_base
from sqlalchemy.orm import Session
from sqlalchemy import create_engine

Base = automap_base()

# engine, suppose it has two tables 'user' and 'address' set up
engine = create_engine("sqlite:///mydatabase.db")

# reflect the tables
Base.prepare(engine, reflect=True)

# mapped classes are now created with names by default
# matching that of the table name.
User = Base.classes.user
Address = Base.classes.address

session = Session(engine)

# rudimentary relationships are produced
session.add(Address(email_address="foo@bar.com", user=User(name="foo")))

# collection-based relationships are by default named
# "_collection"
print (u1.address_collection)

Here is what the above code is Doing:
1. Create a new Engine instance.
2. Create a new MetaData instance.
3. Use the MetaData instance to generate a new Table object, representing the table named “user”.
4. Create a new mapper() instance, using the Table object as the argument.
5. Create a new class called “User”, which will be mapped to the “user” table.
6. Create a new Session instance.
7. Add a new User object to the session.
8. Commit the session.
9. Query the database for the first User object.
10. Print the User object’s name attribute.

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