Fixed #19299 -- Removed Nullification of Foreign Keys To CharFields #1690

albertyw · Sep 29, 2013

This pull request fixes https://code.djangoproject.com/ticket/19299 (and https://code.djangoproject.com/ticket/21194)

charettes · Sep 30, 2013

charettes reviewed Sep 30, 2013

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charettes · Sep 30, 2013

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-        if value == '' or value is None:
+        if value is None:
+            return None
+        elif value == '' and not isinstance(self.related_field, CharField):


I think you should refer to the empty_strings_allowed property of the related field instead of special casing CharField here.

if value is None or (value == '' and not related_field.empty_strings_allowed)

Not sure an extra connection.features.interprets_empty_strings_as_nulls check is also required here since both values will be interpreted as NULL anyway.

I changed it to your suggestion (using self.related_field instead of just related_field) in 61f5df9

bmispelon · Oct 2, 2013

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bmispelon · Oct 2, 2013

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 class FksToBooleans(models.Model):
    """Model wih FKs to models with {Null,}BooleanField's, #15040"""
    bf = models.ForeignKey(BooleanModel)
    nbf = models.ForeignKey(NullBooleanModel)

+class FkToChar(models.Model):
+    """Model with FK to models with {""} #21194"""


Nice touch to follow the previous model's docstring, but I think this one should simply be:
Model with FK to a model with a CharField primarey key, #21194

The {Null,}BooleanField of the previous one just means NullBooleanField and BooleanField.

bmispelon · Oct 2, 2013

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bmispelon · Oct 2, 2013

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@@ -62,11 +62,18 @@ class BooleanModel(models.Model):
    bfield = models.BooleanField(default=None)
    string = models.CharField(max_length=10, default='abc')

+class CharModel(models.Model):


Nitpicky but I'd call it PrimaryKeyCharmodel, just to be more explicit about what it is.

bmispelon · Oct 2, 2013

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bmispelon · Oct 2, 2013

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@@ -62,11 +62,18 @@ class BooleanModel(models.Model):
    bfield = models.BooleanField(default=None)
    string = models.CharField(max_length=10, default='abc')

+class CharModel(models.Model):
+    string = models.CharField(max_length = 10, primary_key=True)


Per pep8, this should be max_length=10 (note the lack of whitespace around the equal sign).

bmispelon · Oct 2, 2013

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bmispelon · Oct 2, 2013

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@@ -140,6 +140,18 @@ def test_callable_default(self):
        b = Bar.objects.create(b="bcd")
        self.assertEqual(b.a, a)

+    def test_get_db_prep_save(self):


Not sure if that's the best name for this test. How about test_empty_string_fk?

bmispelon · Oct 2, 2013

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bmispelon · Oct 2, 2013

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+    def test_get_db_prep_save(self):
+        """
+        Test that foreign key values to empty strings don't get converted
+        to None


Make sure you reference your ticket number in the docstring (see the other tests in the file).

bmispelon · Oct 2, 2013

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bmispelon · Oct 2, 2013

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+        to None
+        """
+        char_model_normal = CharModel.objects.create(string='asdf')
+        fk_model_normal = FkToChar.objects.create(out=char_model_normal)


I don't think the two lines (*_normal) are needed here since this functionality is most likely tested elsewhere (and you don't make use of those variables in your assertions later on).

I did look for tests that used the get_db_prep_save method, but I didn't find any. Agreed, I should actually write an assertion for the normal case, assuming it isn't covered somewhere else.

I just removed the normal case lines because I'm guessing it is covered somewhere else and I just didn't see it. If it isn't covered, it would be outside the scope of this pull request/ticket 21194

bmispelon · Oct 2, 2013

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bmispelon · Oct 2, 2013

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+        char_model_normal = CharModel.objects.create(string='asdf')
+        fk_model_normal = FkToChar.objects.create(out=char_model_normal)
+        char_model_empty = CharModel.objects.create(string='')
+        fk_model_empty = FkToChar.objects.create(out=char_model_empty)


You don't need to assign the result to a variable here.

I do need the pk of the newly created FkToChar model to lookup (and reload) the same object again on the next line.

shaib · Nov 25, 2013

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shaib · Nov 25, 2013

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@@ -141,6 +141,15 @@ def test_callable_default(self):
        b = Bar.objects.create(b="bcd")
        self.assertEqual(b.a, a)

+    def test_empty_string_fk(self):


This test needs to be made to pass or skip when the connection interprets_empty_strings_as_null -- skipIfDBFeature is your friend
(on Oracle, line 149 will raise an IntegrityError).

shaib · Nov 25, 2013

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shaib · Nov 25, 2013

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 class FksToBooleans(models.Model):
    """Model wih FKs to models with {Null,}BooleanField's, #15040"""
    bf = models.ForeignKey(BooleanModel)
    nbf = models.ForeignKey(NullBooleanModel)

+class FkToChar(models.Model):
+    """Model with FK to a model with a CharField primary key, #21194"""


Since 21194 was closed as a dupe, you may want to update the references to 19299.

timgraham · Feb 8, 2014

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timgraham · Feb 8, 2014

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    # object must be non-existent - set the relation to None.
-    if fields[pk_idx] is None or fields[pk_idx] == '':
+    if fields[pk_idx] is None or \


Prefer wrapping the expression in parentheses rather than using a backslash

timgraham · Feb 8, 2014

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timgraham · Feb 8, 2014

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@@ -1320,7 +1321,7 @@ def get_default(self):
        return field_default

    def get_db_prep_save(self, value, connection):
-        if value == '' or value is None:
+        if value is None or (value == '' and (not self.related_field.empty_strings_allowed or connection.features.interprets_empty_strings_as_nulls)):


break this into multiple lines?

timgraham · Feb 8, 2014

Could you please rebase the patch to apply cleanly?

timgraham · Feb 13, 2014

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timgraham · Feb 13, 2014

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@@ -7,7 +7,8 @@
 from django.db.models import signals, Q
 from django.db.models.deletion import SET_NULL, SET_DEFAULT, CASCADE
 from django.db.models.fields import (AutoField, Field, IntegerField,
-    PositiveIntegerField, PositiveSmallIntegerField, FieldDoesNotExist)
+    PositiveIntegerField, PositiveSmallIntegerField, FieldDoesNotExist,
+    CharField)


unused import (please check code with flake8 as there are some "expected 2 blank lines" warnings as well).

timgraham · Feb 13, 2014

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timgraham · Feb 13, 2014

django/db/models/query.py

    # object must be non-existent - set the relation to None.
-    if fields[pk_idx] is None or fields[pk_idx] == '':
+    if (fields[pk_idx] is None or


Could you add a test for this change? If I revert it I don't get any test failures.

There is a test for it. See https://github.com/django/django/pull/1690/files#diff-e4aa8dc49d7522ae55a932ffc7d09c1cR149

Are you running your tests only on databases that interpret empty strings as null values?

I'm trying on SQLite and the new test isn't skipped. If I revert the changes in django/db/models/fields/related.py it fails, but if I revert the change in this file, it still passes.

I see what you mean. I changed tests/model_fields/tests.py:157 so that it would raise an error.

timgraham · Feb 15, 2014

Great, merged in 8bbdcc7, thank-you.

timgraham referenced this pull request Feb 8, 2014
Closed
Don't automatically collapse `''` and `None` for keys. #1197

Fixed #19299 -- Fixed Nullification of Foreign Keys To CharFields

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timgraham closed this Feb 15, 2014

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Fixed #19299 -- Removed Nullification of Foreign Keys To CharFields #1690

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timgraham commented Feb 15, 2014

timgraham closed this Feb 15, 2014

charettes reviewed Sep 30, 2013

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bmispelon reviewed Oct 2, 2013

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bmispelon reviewed Oct 2, 2013

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