can't render element of type <class 'sqlalchemy.dialects.postgresql.base.UUID'>

Question

I saw this snippet of code from Flask-common at line 57:

id = db.Column(UUID, default=lambda: str(uuid.uuid4()), primary_key=True)

So I thought I give it a try and use it in my app's models.py (because I prefer to have uuid type for my id's)

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
from sqlalchemy.dialects.postgresql import UUID
import uuid

from app import db

class CostCenter(db.Model):
    __tablename__ = "costcenter"

    id = db.Column('id', UUID(as_uuid=True), default=lambda: str(uuid.uuid4()), primary_key=True)
    name = db.Column('name', db.Text)

    def __init__(self, name):
        self.name = name

    def __repr__(self):
        return '<id {}>'.format(self.id)

But when I try to run python manage.py db upgrade, it results to an error:

  File "build/bdist.linux-x86_64/egg/sqlalchemy/sql/compiler.py", line 190, in __init__                                                          
  File "build/bdist.linux-x86_64/egg/sqlalchemy/sql/compiler.py", line 213, in process                                                           
  File "build/bdist.linux-x86_64/egg/sqlalchemy/sql/visitors.py", line 81, in _compiler_dispatch                                                 
  File "build/bdist.linux-x86_64/egg/sqlalchemy/sql/compiler.py", line 2164, in visit_create_table                                               
  File "build/bdist.linux-x86_64/egg/sqlalchemy/util/compat.py", line 199, in raise_from_cause                                                   
  File "build/bdist.linux-x86_64/egg/sqlalchemy/sql/compiler.py", line 2153, in visit_create_table                                               
  File "build/bdist.linux-x86_64/egg/sqlalchemy/sql/compiler.py", line 213, in process                                                           
  File "build/bdist.linux-x86_64/egg/sqlalchemy/sql/visitors.py", line 81, in _compiler_dispatch                                                 
  File "build/bdist.linux-x86_64/egg/sqlalchemy/sql/compiler.py", line 2184, in visit_create_column                                              
  File "build/bdist.linux-x86_64/egg/sqlalchemy/dialects/sqlite/base.py", line 847, in get_column_specification                                  
  File "build/bdist.linux-x86_64/egg/sqlalchemy/sql/compiler.py", line 261, in process                                                           
  File "build/bdist.linux-x86_64/egg/sqlalchemy/sql/visitors.py", line 79, in _compiler_dispatch                                                 
sqlalchemy.exc.CompileError: (in table 'costcenter', column 'id'): Compiler <sqlalchemy.dialects.sqlite.base.SQLiteTypeCompiler object at 0x7fc16
c1f1a50> can't render element of type <class 'sqlalchemy.dialects.postgresql.base.UUID'>

Why can't it render the type UUID? It is recognized in SQLAlchemy but how come it can't in Flask-SQLAlchemy?

You can't use a Postgres data type with SQLite. They're two different databases. — dirn
– dirn, Commented Apr 23, 2016 at 4:12
For anyone who gets here and is thinking "but I didn't set my database to sqlite!" -- you probably aren't passing in your postgres connection information into sqlalchemy properly, and so it is defaulting to using sqlite as the database. Check your DB configuration information. — Hartley Brody
– Hartley Brody, Commented Aug 9, 2019 at 18:12
Is there an alternative, where depending on the database type you are working with, it runs one line or another? — SistemasIntegrales
– SistemasIntegrales, Commented Jan 2, 2020 at 22:19

David Chan · Accepted Answer · 2023-02-03 21:08:45Z

21

Your column definition is using a function that only works with postgresql, and your database type is sqlite.

You need this:

id = db.Column(
  'id', 
  db.Text(length=36), 
  default=lambda: str(uuid.uuid4()), 
  primary_key=True)

edited Feb 3, 2023 at 21:08

David Chan

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answered Apr 24, 2016 at 6:27

Burhan Khalid

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2 Comments

anobilisgorse Over a year ago

I only read this by now but it so happened I also resorted to a Text column too. Thanks for this though.

SistemasIntegrales Over a year ago

Text also isn't available in sqlite? I thought all SQLALchemy().types where utilizable in any kind of db.

mehdy · Accepted Answer · 2016-04-24 06:06:53Z

0

You can use UUID just in case of using postgresql database.

answered Apr 24, 2016 at 6:06

mehdy

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