Default value for TextField

[Vitaly Yakubenko]

Hi! I start testing Django 1.7beta1. I use MySQL database.
I add new TextField into my model like that:

class Article(models.Model):
    title = models.CharField(max_length=200)
    pub_date = models.DateField()
    text = models.TextField()
    text2 = models.TextField() #new TextField

When I type "python manage.py makemigrations" I am asked to enter default value.
But BLOB/TEXT columns can't have a default value and if i will type something like 'blabla' then after command "python manage.py migrate" i will see error. I think it is bug :)

[loic84]

Hi @Nevsky, default is actually handled at the Python level, not added to the SQL, so that shouldn't be an issue.

I can reproduce that adding a TextField() triggers the questioner which is probably confusing, I wonder if we can't just use '' as default automatically when default=NOT_PROVIDED and empty_strings_allowed=True. Accepting the ticket on this basis.

Regarding the error with 'blabla', did you actually type the quotes? That prompt interprets Python, so if you just type blabla it'll throw an error because it can't find a variable named "blabla".

[Vitaly Yakubenko]

Replying to loic84:

I can reproduce that adding a TextField() triggers the questioner which is probably confusing, I wonder if we can't just use as default automatically when default=NOT_PROVIDED and empty_strings_allowed=True. Accepting the ticket on this basis.

Yes I think correct is to use "None" as default in this instance.

Regarding the error with 'blabla', did you actually type the quotes? That prompt interprets Python, so if you just type blabla it'll throw an error because it can't find a variable named "blabla".

Yes, I type the quotes and migration successfully making. I confused commands "migrate" and "magemigrations" in ticked description. I get error when I trying to apply created migration because it contains default value for field that can't have default value in MySQL database :)

[Tim Graham]

Loic, I'm not sure using '' as an automatic default is better than the current situation. Why not give the user the option of entering something else besides that (especially if blank=False)?

[loic84]

Fixed the name of the commands in the ticket description.

I originally assumed this was an issue before the migrate step, but it's indeed an SQL issue due to one-off defaults, Django uses db defaults for these.

The fix for MySQL is to not provide a default for BLOB/TEXT in the SchemaEditor. Although we'll now need to propagate the default value manually.

[loic84]

@Nevsky could you check if this solves your problem? ​https://github.com/django/django/pull/2634

[Andrew Godwin]

loic84: That PR looks like the right approach to me; will MySQL reject any default value on blob/text columns or just empty ones? Oracle has a weird behaviour where it treats empty strings as NULL on text columns that causes similar issues, but we have a fix for that.

[loic84]

MySQL rejects anything even remotely related to a default for blob/text columns (i.e. ALTER TABLE 'table' ALTER COLUMN 'blob' DROP DEFAULT).

[Denis Cornehl]

I'll have a look at it and verify the fix.

(atm I get Nevsky's error when adding the column without the fix, with the fix I get another error. But checking it.

[Denis Cornehl]

Update the PR with some comments:
​https://github.com/django/django/pull/2634

short version:
PR failing when there are empty or string defaults.
But with fixed everything (in this ticket) seems fine.

[loic84]

Updated the PR to fix the issue reported by @syphar and to incorporate the fix for #22626.

Sadly the handling of bytes/strings is still less than ideal in the many quote_value:

• " in a default will break SQLite and MySQL.
• Oracle doesn't support bytes so breaks on BinaryField.
• Oracle uses repr to quote six.string_types, which will probably result in an extra u prefix.

I propose we open a new ticket to deal with this issue separately.

[Collin Anderson]

#22649 SchemaEditor.quote_value is very fragile.

[Loic Bistuer <loic.bistuer@…>]

In 6aacb4c9915c83a897dbde0b11cc46131fc7d16e:

Fixed #22626 -- Allow BinaryField defaults with SQlite.

Also fixes a slight issue in sqlite3.schema._remake_table where
default values where quoted with "column name" quoting rules.

Reference for quoting: ​http://www.sqlite.org/lang_expr.html

Thanks Shai Berger for the review. Refs #22424.

[Loic Bistuer <loic.bistuer@…>]

In 1d3d01b4f74f80655ac354f7a39e3908a9b41b14:

Fixed #22424 -- Fixed handling of default values for TextField/BinaryField on MySQL.

Thanks syphar for the review and suggestions.

[Andrew Godwin <andrew@…>]

In 4e32e47348473757280ca7a8d78edf6011fe65a3:

Merge pull request #2634 from loic/ticket22424

Fixed #22424 -- MySQL doesn't accept migrations' one-off default values ...

[Tim Graham <timograham@…>]

In 1a29675d76de00d6fad9b366fc66e8b6d541c3b6:

[1.7.x] Fixed #22626 -- Allow BinaryField defaults with SQlite.

Also fixes a slight issue in sqlite3.schema._remake_table where
default values where quoted with "column name" quoting rules.

Reference for quoting: ​http://www.sqlite.org/lang_expr.html

Thanks Shai Berger for the review. Refs #22424.

Backport of 6aacb4c991 from master

[Tim Graham <timograham@…>]

In d61b6224b09cb2aa6fb75ccecab246f91553ef7b:

[1.7.x] Fixed #22424 -- Fixed handling of default values for TextField/BinaryField on MySQL.

Thanks syphar for the review and suggestions.

Backport of 1d3d01b4f7 from master