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?

Answer 1

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)