Default behavior for sqlalchemy_utils.UUIDType

[Jason Libbey]

Hi, this is my first post, so if it does not adhere by your guidelines, please let me know and I'll fix it ASAP.

I'm using the sqlalchemy_utils.UUIDType as per backend-agnostic-guid-type.

from sqlalchemy_utils import UUIDType

class ApplicationStore(Base, Timestamp):

    __tablename__ = 'applications'

    id = Column(UUIDType(binary=False), primary_key=True, default=uuid.uuid4)

    user_uuid = Column(UUIDType(binary=False), unique=True, index=True, nullable=False)

Since I am using a mysql db, the UUIDType is correctly falling back to the CHAR32 representation.  However, the value that gets written to the db is the uuid with no dashes.

application = application_service.create(user_uuid=uuid.uuid4())

The string representation of the uuid shows it with dashes, but the database char is saved without dashes.  So my questions are:

1. Am I using this correctly?

2. Is this the expected behavior?

3. How can I force it to save as uuid with dashes, while still using the backend agnostic guid type?

Python version: 2.7.10

SQLAlchemy version: 1.0.12

[Mike Bayer]

On 07/29/2016 09:45 PM, Jason Libbey wrote:
> Hi, this is my first post, so if it does not adhere by your guidelines,
> please let me know and I'll fix it ASAP.
>
> I'm using the sqlalchemy_utils.UUIDType as per
> backend-agnostic-guid-type

> <http://docs.sqlalchemy.org/en/latest/core/custom_types.html#backend-agnostic-guid-type>.

OK


>
> from sqlalchemy_utils import UUIDType

OK that is something else, UUIDType is probably taken from the recipe
here but if you're importing that from the third-party sqlalchemy_utils
as opposed to typing out the GUID type directly, then the change I'm
giving you below is not possible, you need to either talk to them or use
the recipe type directly.

>
>
>
> class ApplicationStore(Base, Timestamp):
>
> __tablename__ = 'applications'
>
> id = Column(UUIDType(binary=False), primary_key=True, default=uuid.uuid4)
>
> user_uuid = Column(UUIDType(binary=False), unique=True, index=True, nullable=False)
>
>
>
> Since I am using a mysql db, the UUIDType is correctly falling back to
> the CHAR32 representation. However, the value that gets written to the
> db is the uuid with no dashes.

that's because the recipe is using the int value of the object (though I
don't know what the 'binary' flag on the sqlalchemy_utils version does):

>>> some_uuid = str(uuid.uuid4())
>>> print some_uuid
57e8077f-0f12-4d0f-9ef6-2a45ac70a4bf

>>> print "%.32x" % uuid.UUID(some_uuid).int
57e8077f0f124d0f9ef62a45ac70a4bf

>
>
> application = application_service.create(user_uuid=uuid.uuid4())
>
>
>
> The string representation of the uuid shows it with dashes, but the
> database char is saved without dashes. So my questions are:
> 1. Am I using this correctly?

probably, sqlalchemy_utils person would know for sure

> 2. Is this the expected behavior?

yes

> 3. How can I force it to save as uuid with dashes, while still using the
> backend agnostic guid type?

first question is, why. the dashes just take up useless space.
Let's assume you want MySQL console behavior to print the dashes without
you having to do anything to the value, OK. use the GUID recipe from
the documentation, change it to use char(36) (four more characters to
save the dashes) and change the string conversion part to just use
str(uuid) instead of the above "%.32x" conversion.

>
> Python version: 2.7.10
> SQLAlchemy version: 1.0.12
>

> --
> You received this message because you are subscribed to the Google
> Groups "sqlalchemy" group.
> To unsubscribe from this group and stop receiving emails from it, send
> an email to sqlalchemy+...@googlegroups.com
> <mailto:sqlalchemy+...@googlegroups.com>.
> To post to this group, send email to sqlal...@googlegroups.com
> <mailto:sqlal...@googlegroups.com>.
> Visit this group at https://groups.google.com/group/sqlalchemy.
> For more options, visit https://groups.google.com/d/optout.

[Jason Libbey]

I see, so I didn't quite understand the relationship between sqlalchemy and the sqlalchemy_utils libraries, but I think I've got it all straight now.  To answer your question as to why I would need the dashes, it's because the other dependencies expect to be able to look up uuid by the standard format.  At any rate, I've got it fixed now, thanks so much Mike!