Modifying existing value in SQLAlchemy object

Question

I'm trying to take an existing string in a retrieved SQLAlchemy object and concatenate it with a second string, however no value is being written.

print(messages)
testsuite = session.query(Testsuite).get(test_id)
testsuite.console += messages
session.commit()

Inspecting the database, the record has kept its original empty value - messages was never added.

My Testsuite model is as follows:

# Represents schema - used by engine to create tables etc.
Base = declarative_base()


# These SQL fields are horrendously inefficient - need replacing ASAP!
class Testsuite(Base):
    """Testsuite model to map testsuite in progress to SQL DB."""

    __tablename__ = 'testsuites'

    id = Column(Integer, primary_key=True)
    name = Column(String)
    timestamp = Column(DateTime, default=datetime.datetime.utcnow)
    product_name = Column(String)
    serial_number = Column(String)
    total_tests = Column(Integer)
    completed_tests = Column(Integer)
    console = Column(Text)
    report_id = Column(Integer)
    testcases = relationship('Testcase', backref='testsuite')
    result = Column(String)

    def __init__(self, testsuite_name, product_name, serial_number, total_tests=0):
        self.name = testsuite_name
        self.product_name = product_name
        self.serial_number = serial_number
        self.total_tests = total_tests
        self.completed_tests = 0
        self.result = 'pending'

I've read that the way I am modifying my objects can lead to race conditions, though I am unsure of a suitable alternative. Can anyone point out the issues with what I'm doing and why my messages string isn't being added?

Thanks :)

Please post how you build your model. Perhaps '''testsuite.console''' isn't what you think it is. — knitti
– knitti, Commented Jul 17, 2014 at 9:05

Mike Wild · Accepted Answer · 2014-07-17 10:04:04Z

1

So after a bit of experimentation, it seems that the code was failing because Testsuite.console never had an initial value.

The code now works with the following change to the mode:

class Testsuite(Base):
    """Testsuite model to map testsuite in progress to SQL DB."""

    __tablename__ = 'testsuites'

    id = Column(Integer, primary_key=True)
    name = Column(String)
    timestamp = Column(DateTime, default=datetime.datetime.utcnow)
    product_name = Column(String)
    serial_number = Column(String)
    total_tests = Column(Integer)
    completed_tests = Column(Integer, default=0)
    console = Column(String, default="Waiting for incoming log data...\n")
    report_id = Column(Integer)
    testcases = relationship('Testcase', backref='testsuite')
    result = Column(String, default='pending')

    def __init__(self, testsuite_name, product_name, serial_number, total_tests=0):
        self.name = testsuite_name
        self.product_name = product_name
        self.serial_number = serial_number
        self.total_tests = total_tests

answered Jul 17, 2014 at 10:04

Mike Wild

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2 Comments

knitti Over a year ago

interesting... +1 for finding the solution yourself. Would you mind posting which RDBMS you use? I did never run into this problem with Postgres...

Mike Wild Over a year ago

Certainly, I'm using SQLite 3.

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