Question

What I am trying to do is to get from SqlAlchemy entity definition all it’s Column()’s, determine their types and constraints, to be able to pre-validate, convert data and display custom forms to user.

How can I introspect it?

Example:

class Person(Base):
    '''
        Represents Person
    '''
    __tablename__ = 'person'

    # Columns
    id = Column(String(8), primary_key=True, default=uid_gen)
    title = Column(String(512), nullable=False)
    birth_date = Column(DateTime, nullable=False)

I want to get this id, title, birth date, determine their restrictions (such as title is string and max length is 512 or birth_date is datetime etc)

Thank you

Answer 1

If you are using sqlalchemy 0.8, then you should check out the new feature New Class Inspection System. Sample code extract from the documentation:

class User(Base):
    __tablename__ = 'user'

    id = Column(Integer, primary_key=True)
    name = Column(String)
    name_syn = synonym(name)
    addresses = relationship(Address)

# universal entry point is inspect()
>>> b = inspect(User)

# column collection
>>> b.columns
[<id column>, <name column>]

Otherwise, see Accessing Tables and Columns part of the documentation. Again, code extract from the docu:

employees = Table(...)
# or if using declarative
#employees = Employee.__table__

# or just
employees.c.employee_id

# via string
employees.c['employee_id']

# iterate through all columns
for c in employees.c:
    print c

# access a column's name, type, nullable, primary key, foreign key
employees.c.employee_id.name
employees.c.employee_id.type
employees.c.employee_id.nullable
employees.c.employee_id.primary_key
employees.c.employee_dept.foreign_keys