OK. I removed the maxcharlength from dal.py (in trunk).
We now need to understand what will happen to existing mysql apps.
On Saturday, 22 June 2013 13:55:01 UTC-5, Anthony wrote:
>
> In general, I would say it's not a good idea to silently change the
> explicitly set length of a field. Either pass the length to the database
> and let the database throw an exception, or raise an exception in web2py
> (the former is probably preferable, since web2py won't know the true limit
> of the particular database version).
>
> Anthony
>
> On Saturday, June 22, 2013 2:16:58 PM UTC-4, Massimo Di Pierro wrote:
>>
>> There are historical reason for this and I do not oppose to change it
>> since modern mysql versions support longer varchar.
>> You can change this yourlself:
>>
>> db = DAL('mysql://...'_
>> db._adapter.maxcharlength = 1024 # or whatever you want
>>
>> If we change the default in web2py this would trigger a migration. Can
>> you help us test it?
>> Should we change it or remove the check completely. Whatever value we set
>> it to (for mysql and other dbs) it will change in the future and we will
>> run in the same problem. Should web2py perhaps have a check and raise an
>> error? Or should it pass the length to the db without checks?
>>
>>
>>
>>
>>
>>
>> On Saturday, 22 June 2013 11:46:33 UTC-5, Chris wrote:
>>>
>>> Derek, the main issue isn't truncation at insert time. In a web2py
>>> DAL-mediated create table statement, DAL code unilaterally reduces MySQL
>>> varchar lengths to 255, whether the specific version of MySQL could
>>> tolerate a longer varchar or not. The developer says, column abc should be
>>> varchar(1000); DAL runs the define_table; the resulting column is
>>> varchar(255); no error is raised; developer has no reason to think there's
>>> a problem; then inserts data and mySQL silently truncates (corrupts) it.
>>> The DAL problem would be equally bad, although easier for the developer to
>>> notice / and sooner, if MySQL didn't perform truncation. The fact that
>>> MySQL performs truncation silently makes it that much more important that
>>> DAL not change the column definition silently.
>>>
>>> If I use the mysql command line tool, create table xyz (abc
>>> varchar(1000)) results in a column of length 1000. If I use the logically
>>> equivalent DAL define_table statement, it results in a column of length
>>> 255. The two approaches, given the same inputs, really should have the
>>> same outcome.
>>>
>>> The behavior is also inconsistent among DB engines. For any DBMS other
>>> then MySQL, DAL enforces a max varchar length of 2^15. However, Oracle 9i
>>> has a max varchar length of 4000; SQL Server 2005 has a max of 8000; etc.
>>> Many DBMS versions have some limit. In those cases, DAL attempts to
>>> define the table per the developer's instructions and returns a
>>> DBMS-specific error if a column length is unacceptable. The same should be
>>> done for MySQL.
>>>
>>> The correct behavior is to return an error if the developer issues a
>>> define_table statement that can't be fulfilled by the database layer.
>>>
>>>
>>>
>>>
>>> On Wednesday, June 19, 2013 7:15:44 PM UTC-4, Derek wrote:
>>>>
>>>> It's not web2py's fault that MySQL silently truncates data.
>>>>
>>>> http://www.davidpashley.com/blog/databases/mysql/silently-truncated
>>>>
>>>>
>>>> On Wednesday, June 19, 2013 5:52:26 AM UTC-7, Chris wrote:
>>>>>
>>>>> The main problem is that the failure is silent. It makes no sense
>>>>> that a developer declares a field to be length 1000, and DAL arbitrarily
>>>>> reduces that to 255 instead of providing an error message. I understand
>>>>> why 255 may be a safe default limit for MySQL; but if so then fail the
>>>>> field creation with a relevant error message (and maybe reference
>>>>> Jonathan's solution re: how to override maxcharlength if the developer
>>>>> knows the DBMS version can handle the larger limit).
>>>>>
>>>>> In the current 2.5.1 code, looking in dal.py:
>>>>>
>>>>> class MySQLAdapter(BaseAdapter):
>>>>> ....
>>>>> maxcharlength = 255
>>>>>
>>>>> ...
>>>>>
>>>>> class Table(object):
>>>>> ...
>>>>> def __init__( self,
>>>>> db,
>>>>> tablename,
>>>>> *fields,
>>>>> **args
>>>>> ):
>>>>> ...
>>>>> for field in fields:
>>>>> ...
>>>>> if db and not field.type in ('text', 'blob', 'json') and \
>>>>> db._adapter.maxcharlength < field.length:
>>>>> field.length = db._adapter.maxcharlength ### problem
>>>>> line
>>>>>
>>>>>
>>>>> I'd recommend the last line above, marked ### problem line, be
>>>>> replaced with something like, raise ValueError('Requested field length
>>>>> exceeds adapter maxcharlength, cannot create. See http://whateverfor a
>>>>> way to override this limit.')
>>>>>
>>>>> ??
>>>>>
>>>>
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