How to print all columns in SQLAlchemy ORM

Question

Using SQLAlchemy, I am trying to print out all of the attributes of each model that I have in a manner similar to:

SELECT * from table;

How

Answer 1

Take a look at SQLAchemy's metadata reflection feature.

A Table object can be instructed to load information about itself from the corresponding database schema object already existing within the database. This process is called reflection.

Answer 2

I use this because it's slightly shorter:

for m in session.query(*model.__table__.columns).all():
    print m

Answer 3

Put this together and found it helpful:

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
engine = create_engine('mysql+pymysql://testuser:password@localhost:3306/testdb')
DeclarativeBase = declarative_base()
metadata = DeclarativeBase.metadata
metadata.bind = engine


# configure Session class with desired options
Session = sessionmaker()

# associate it with our custom Session class
Session.configure(bind=engine)

# work with the session
session = Session()

And then:

d = {k: metadata.tables[k].columns.keys() for k in metadata.tables.keys()}

Example output print(d):

{'orderdetails': ['orderNumber', 'productCode', 'quantityOrdered', 'priceEach', 'orderLineNumber'], 
'offices': ['addressLine1', 'addressLine2', 'city', 'country', 'officeCode', 'phone', 'postalCode', 'state', 'territory'],
'orders': ['comments', 'customerNumber', 'orderDate', 'orderNumber', 'requiredDate', 'shippedDate', 'status'],
'products': ['MSRP', 'buyPrice', 'productCode', 'productDescription', 'productLine', 'productName', 'productScale', 'productVendor', 'quantityInStock'],
'employees': ['employeeNumber', 'lastName', 'firstName', 'extension', 'email', 'officeCode', 'reportsTo', 'jobTitle'], 
'customers': ['addressLine1', 'addressLine2', 'city', 'contactFirstName', 'contactLastName', 'country', 'creditLimit', 'customerName', 'customerNumber', 'phone', 'postalCode', 'salesRepEmployeeNumber', 'state'],
'productlines': ['htmlDescription', 'image', 'productLine', 'textDescription'],
'payments': ['amount', 'checkNumber', 'customerNumber', 'paymentDate']}

OR and then:

from sqlalchemy.sql import text
cmd = "SELECT * FROM information_schema.columns WHERE table_schema = :db ORDER BY table_name,ordinal_position"
result = session.execute(
            text(cmd),
            {"db": "classicmodels"}
        )
result.fetchall()

Answer 4

I'm using SQL Alchemy v 1.0.14 on Python 3.5.2

Assuming you can connect to an engine with create_engine(), I was able to display all columns using the following code. Replace "my connection string" and "my table name" with the appropriate values.

from sqlalchemy import create_engine, MetaData, Table, select

engine = create_engine('my connection string')

conn = engine.connect()
metadata = MetaData(conn)
t = Table("my table name", metadata, autoload=True)
columns = [m.key for m in t.columns]
columns

the last row just displays the column names from the previous statement.

Answer 5

You may be interested in what I came up with to do this.

from sqlalchemy.orm import class_mapper
import collections

# structure returned by get_metadata function.
MetaDataTuple = collections.namedtuple("MetaDataTuple", 
        "coltype, colname, default, m2m, nullable, uselist, collection")


def get_metadata_iterator(class_):
    for prop in class_mapper(class_).iterate_properties:
        name = prop.key
        if name.startswith("_") or name == "id" or name.endswith("_id"):
            continue
        md = _get_column_metadata(prop)
        if md is None:
            continue
        yield md


def get_column_metadata(class_, colname):
    prop = class_mapper(class_).get_property(colname)
    md = _get_column_metadata(prop)
    if md is None:
        raise ValueError("Not a column name: %r." % (colname,))
    return md


def _get_column_metadata(prop):
    name = prop.key
    m2m = False
    default = None
    nullable = None
    uselist = False
    collection = None
    proptype = type(prop)
    if proptype is ColumnProperty:
        coltype = type(prop.columns[0].type).__name__
        try:
            default = prop.columns[0].default
        except AttributeError:
            default = None
        else:
            if default is not None:
                default = default.arg(None)
        nullable = prop.columns[0].nullable
    elif proptype is RelationshipProperty:
        coltype = RelationshipProperty.__name__
        m2m = prop.secondary is not None
        nullable = prop.local_side[0].nullable
        uselist = prop.uselist
        if prop.collection_class is not None:
            collection = type(prop.collection_class()).__name__
        else:
            collection = "list"
    else:
        return None
    return MetaDataTuple(coltype, str(name), default, m2m, nullable, uselist, collection)

Answer 6

I believe this is the easiest way:

print [cname for cname in m.__dict__.keys()]

EDIT: The answer above me using sqlalchemy.inspection.inspect() seems to be a better solution.