I have already tables for Vehicle and Car, Using this django-positions for postioning my items of the tables. For that i have added the positon field in both the models.
class Vehicle(models.Model):
name = models.CharField(max_length=50)
slug = models.SlugField(max_length=50, unique=True)
position = PositionField()
And
class Car(models.Model):
name = models.CharField(max_length=50)
slug = models.SlugField(max_length=50, unique=True)
vehicle = models.ForeignKey(Vehicle, related_name="vehicle")
position = PositionField()
makemigrations ran fine but while migrate getting following error. using postgreSQL
django.db.utils.IntegrityError: check constraint "myapp_vehicle_position_check" is violated by some row
It turns out that during the migration the SQL code checks for the value of the PositionField to be greater than or equal to 0. The default being -1 for automatic ordering the migration fails.
I haven't digged any more but as a turnaround changing the default value to something equal or above zero allow for the migration to be successful.
class Vehicle(models.Model):
name = models.CharField(max_length=50)
slug = models.SlugField(max_length=50, unique=True)
position = PositionField(default=99)
Hope this helps.
Related
I have this models in my Django ganalytics app:
class Article(models.Model):
id = models.IntegerField(unique=True, primary_key=True)
article_title = models.CharField(max_length=250)
article_url = models.URLField(max_length=250)
article_pub_date = models.DateField()
class Company(models.Model):
company_name = models.CharField(max_length=250)
class Author(models.Model):
author_sf_id = models.CharField(max_length=20, null=True)
author_name = models.CharField(max_length=250)
class AuthorArticleCompany(models.Model):
author = models.ForeignKey(Author,
to_field="id",
on_delete=models.CASCADE,
related_name='authorarticle_author_id')
company = models.ForeignKey(Company,
to_field="id",
on_delete=models.CASCADE,
related_name='authorarticle_company_id')
article = models.ForeignKey(Article,
to_field="id",
on_delete=models.CASCADE,
related_name='authorarticle_article_id')
class Ganalytics(models.Model):
article = models.ForeignKey(Article,
on_delete=models.CASCADE,
related_name='ganalytics_author_id')
totalview = models.IntegerField()
totalinteractions = models.IntegerField()
class Unsubscribers(models.Model):
email = models.EmailField()
reasonwhy = models.CharField(max_length=90)
I am running pandas to_sql to upload the database:
authorarticlecompanydf.to_sql("ganalytics_authorarticlecompany", con=engine, if_exists="append", index=False)
articledf.to_sql("ganalytics_article",con=engine,if_exists="replace",index=False)
company_name.to_sql("ganalytics_company",con=engine,if_exists="replace",index=False)
authordf.to_sql("ganalytics_author", con=engine,if_exists="replace", index=False)
I am getting this error message:
DETAIL: constraint ganalytics_ganalytic_article_id_d37f2464_fk_ganalytic on table ganalytics_ganalytics depends on table ganalytics_article
constraint ganalytics_authorart_article_id_7f4ff374_fk_ganalytic on table ganalytics_authorarticlecompany depends on table ganalytics_article
HINT: Use DROP ... CASCADE to drop the dependent objects too.
[SQL:
DROP TABLE ganalytics_article]
I have tried to change the on_delete field to different values but it wont help.
What am I doing wrong?
What is the command you are running to get the error? The bottom line is Ganalytics depends on Article via the FK between them. By dropping Article first you are breaking that dependency. You either need to DROP Ganalytics first and then Article or follow the hint DROP ... CASCADE. Though be aware that will DROP Ganalytics also.
UPDATE
Another option would be to drop the FK between the two tables. Then you would not have the dependency issue.
I'm working on the Django section of CS50 around the 30min mark on the video with the modes 'ForeignKey' section.
When i run the make migration i get the error.
You are trying to add a non-nullable field 'agent' to product without a default; we can't do that (the database needs something to populate existing rows).
Please select a fix:
1) Provide a one-off default now (will be set on all existing rows with a null value for this column)
2) Quit, and let me add a default in models.py
Select an option: 2
if I set the default as a string value i get the error saying it was expecting an id.
If i set it as 1 then i get the following.
The row in table 'clutter_product' with primary key '1' has an invalid foreign key: clutter_product.agent_id contains a value '1' that does not have a corresponding value in clutter_supplier.id.
class Supplier(models.Model):
company = models.CharField(max_length=64)
contact = models.CharField(max_length=64)
email = models.CharField(max_length=128, blank = True)
def __str__(self):
return f"{self.id} {self.company} {self.contact} {self.email}"
class Product(models.Model):
name = models.CharField(max_length=64)
sku = models.CharField(max_length=64, blank = True)
unit_cost = models.IntegerField()
rrp = models.IntegerField()
average_fee = models.IntegerField()
shipping_fee = models.IntegerField()
agent = models.ForeignKey(Supplier, default=1, on_delete=models.CASCADE, related_name="suppliers")
I would suggest to try these steps:
First, delete the migration file which is causing this problem.
Second change the model like this:
class Product(models.Model):
# rest of the fields
agent = models.ForeignKey(Supplier, null=True, default=None, on_delete=models.CASCADE, related_name="suppliers")
Third run makemigrations and migrate.
Fourth create a instance of supplier using supplier = Supplier.objects.create(company="ABC", contact="contact", email="a#b.c", pk=1)
Fifth(optional) Update the existing Product to haven a supplier-Product.objects.update(agent=supplier).
Sixth, if you want to constrain Products to be created with an agent, then remove null=True, default=None from agent field in Product model. Then run makemigrations and migrate.
I want to set a foreign key to a field of another model.
I have tried Foreign Key to_field='field_name'
class Banks(models.Model):
name = models.TextField()
id = models.IntegerField(unique=True)
class Meta:
db_table = 'banks'
class Branches(models.Model):
ifsc = models.CharField(max_length=20, null=False)
bank_id = models.ForeignKey(Banks, to_field='id', on_delete=models.CASCADE)
branch = models.CharField(max_length=50)```
ProgrammingError: column branches.id does not exist
LINE 1: SELECT "branches"."id", "branches"."ifsc", "branches"."bank_...
Just add unique=True in the name column, in the Banks model.
class Banks(models.Model):
name = models.TextField(unique=True) # Just add unique=True
id = models.IntegerField(unique=True, primary_key=True)
class Meta:
db_table = 'banks'
class Branches(models.Model):
ifsc = models.CharField(max_length=20, null=False)
bank_id = models.ForeignKey(Banks, to_field='id', on_delete=models.CASCADE) # Now it will work
branch = models.CharField(max_length=50)
This problem is not caused by the foreign key. The error is happening in the Branches model, which presumably also has a db_table Meta attribute and is based on a legacy table.
You must define a primary key for your models. If you don't, Django will do so automatically and call it id. In the case of your Banks model, you should set that id field as primary_key=True - or indeed remove it completely, since that is the default. You need to find a suitable pk for Branches as well and declare it in the field.
For your actual question, you don't need to do anything; Django will automatically set the FK to point to the PK of the target model.
class Bank(models.Model):
# removed `id` as that is the default PK
name = models.TextField()
class Meta:
db_table = 'banks'
class Branch(models.Model):
ifsc = models.CharField(max_length=20, primary_key=True) # assume this is the PK
bank = models.ForeignKey(Bank, on_delete=models.CASCADE)
branch = models.CharField(max_length=50)
class Meta:
db_table = 'branches'
Note also, since these are legacy tables you probably want to add managed = False to both Meta classes. And as suggested by AKX, it is Django style to make model names singular; you can do that without affecting the table name since that is declared explicitly.
I have created the following model:
class World(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
name = models.CharField(max_length=200)
setting = models.CharField(max_length=200)
creation_date = models.DateTimeField('date created')
when I run manage.py makemigrations I get the following error:
You are trying to add a non-nullable field 'id' to world without a default; we can't do that (the database needs something to populate existing rows).
Please select a fix:
1) Provide a one-off default now (will be set on all existing rows with a null value for this column)
2) Quit, and let me add a default in models.py
Why does Django think I have an id field, and how do I get rid of this error?
I had previously set an ID field in my World model, this was confusing something as I had deleted it, I have added the line:
id = models.AutoField(primary_key=True)
When i ran makemitigrations again it asked me if I had renamed the ID field to this new one and I clicked yes and this sorted it out.
My model is now:
class World(models.Model):
id = models.AutoField(primary_key=True)
user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, default='')
name = models.CharField(max_length=200)
setting = models.CharField(max_length=200)
creation_date = models.DateTimeField('date created')
Env: Django 1.8.11 + Postgis
I'm adding some ForeignKeys on a MyModel.
The models pointed are in another schema ("cartography").
makemigrations
no errors
migrate
One error. Can't create the constraint because the generated name.
But I'm adding 10 fields, really similar between them. Only one is giving that stupid error.
I can't specify the constraint name anywhere.
class myModel(models.Model)
zps_calculated = models.ForeignKey( Cartography_zps, verbose_name="zps_calcolato", null=True, blank=True, on_delete=models.SET_NULL)
zsc_sic_sir_calculated = models.ForeignKey( Cartography_zsc_sic_sir, verbose_name="zsc_sic_sir_calcolato", null=True, blank=True, on_delete=models.SET_NULL)
manyothersdata = "xxx"
That is the slice of code generated from sqlmigrate (to inspect the code the migration generate).
As you see the name of the constraint is the error.
1 on 10 fields is giving the error
CREATE INDEX "segnalazioni_f38ba181" ON "segnalazioni" ("zps_calculated_id");
ALTER TABLE "segnalazioni" ADD CONSTRAINT "se_zps_calculated_id_6844dce0603174b2_fk_"cartography"."zps"_id" FOREIGN KEY ("zps_calculated_id") REFERENCES "cartography"."zps" ("id") DEFERRABLE INITIALLY DEFERRED;
CREATE INDEX "segnalazioni_eb52e53f" ON "segnalazioni" ("zsc_sic_sir_calculated_id");
ALTER TABLE "segnalazioni" ADD CONSTRAINT "cc6ce48808e3a5292779a9787d21e5ad" FOREIGN KEY ("zsc_sic_sir_calculated_id") REFERENCES "cartography"."zsc_sic_sir" ("id") DEFERRABLE INITIALLY DEFERRED;
That is the name giving the error: "se_zps_calculated_id_6844dce0603174b2_fk_"cartography"."zps"_id"
I think should be something like:
"6844dce0603174b2..."
the model NOT giving the error:
class Cartography_zsc_sic_sir(models.Model):
id = models.AutoField(primary_key=True)
slug = models.CharField(max_length=40, blank=True, null=True)
nome = models.CharField(max_length=60, blank=True, null=True)
the_geom = models.MultiPolygonField(srid=23032, blank=True, null=True )
objects = models.GeoManager()
class Meta:
managed = False
db_table = '"cartography"."zsc_sic_sir"'
verbose_name = 'Cartography - zsc_sic_sir'
verbose_name_plural = 'Cartography - zsc_sic_sir'
ordering = ["id","slug"]
def __unicode__(self):
return self.nome
that is the model giving the error:
class Cartography_zps(models.Model):
id = models.AutoField(primary_key=True)
slug = models.CharField(max_length=40, blank=True, null=True)
the_geom = models.MultiPolygonField(srid=23032, blank=True, null=True )
objects = models.GeoManager()
class Meta:
managed = False
db_table = '"cartography"."zps"'
verbose_name = 'Cartography - ZPS'
verbose_name_plural = 'Cartography - ZPS'
ordering = ["id","slug"]
def __unicode__(self):
return self.slug
Going further I'm investigating in Django code, backwards.
The
' %s ADD CONSTRAINT %s FOREIGN KEY (%s) REFERENCES %s (%s)%s;' %
is in
/django/db/backends/base/creation.py row 180
using that
qn = self.connection.ops.quote_name
that SHOULD be the %s constraint name value:
qn(truncate_name(r_name, self.connection.ops.max_name_length()))
Anyone have an hint to help me?
I'm gonna look what qn does.
https://github.com/django/django/releases/tag/1.8.11
The problem was the attribute name (but I still dunno why):
zps_calculated = models.ForeignKey( Carto...
I renamed it to
zpsasd_calculated = models.ForeignKey( Carto
and the generated constraint name changed to (sqlmigrate):
a326518e5e22b0c2c1251e5bbb331adb
Wow!
Renamed the attribute zpsasd_calculated to zps_calculated, with another migration.
Worked.
Next time I will migrate with custom SQL
https://www.ralphlepore.net/custom-foreign-key-constraints-with-django/