I am creating a Django web app. I have set a field as a primary key and a unique field. When I try to edit it and give it the same value as another item in the primary key column, the current item got duplicated and each value goes to one of them as shown below.
This is my code from models.py:
class Car(models.Model):
class Meta:
verbose_name = "Car"
verbose_name_plural = "Cars"
car_id = models.CharField(verbose_name='Car ID', max_length=10000, primary_key=True, unique=True)
Some screenshots from the admin panel:
Once you change the primary key, Django will execute an update statement for that id so corrputing your data, the best way as mentioned by #vishal-singh, is to set the id field as Read-only.
Related
class Plans(models.Model):
id = models.IntegerField(primary_key=True)
name = models.CharField(max_length=255)
plan_type = models.CharField(max_length=255)
class Order(models.Model):
id = models.IntegerField(primary_key=True)
selected_plan_id = models.IntegerField(primary_key=True)
Order's selected_plan_id is Plans's id.
Which model should I add a foreign key to? How?
First of all there are some bad ways to pointout:
two fields cannot be primary keys in a table
also django as default includes primary key id in every table, so no need to add id field.
You should be doing this way:
class Order(models.Model):
selected_plan_id = models.ForeignKey(Plans, on_delete=models.CASCADE)
The solution that you are looking for
class Order(models.Model):
id = models.IntegerField(primary_key=True)
selected_plan_id = models.ForeignKey(Plans, on_delete=models.CASCADE)
The purpose of using models.CASCADE is that when the referenced object is deleted, also delete the objects that have references to it.
Also i dont suggest to you add 'id' keyword to your property, django makes automatically it. If you add the 'id' keyword to end of the your property like this case, you gonna see the column called 'selected_plan_id_id' in your table.
class Order(models.Model):
id = models.IntegerField(primary_key=True)
selected_plan_id = models.IntegerField(primary_key=True)
Plain= models.ForeignKey(Plain)
Check the dependence of the table and after getting that made one key as foreign like in this one plain is not depend on the order. But the order depends on the plan.
i have an error in my django admin:
(1054, "Unknown column 'flora2estado.id' in 'field list'")
the model flora2estado has two fields, they are used in unique together as a pseudo composite key, how can i fix this?
admin.py
admin.site.register(Flora2Estado)
models.py
estado = models.OneToOneField(Estados, models.DO_NOTHING, primary_key=True)
especie_id = models.IntegerField()
flora2estado = models.IntegerField(blank=True, null=True)
class Meta:
managed = False
db_table = 'flora2estado'
unique_together = (('estado', 'especie_id'),)
I tried to add the "flora2estado" field without sucess.
All migrations done, thank you for your time
Django is trying to select id field, as documented
By default, Django gives each model the following field:
id = models.AutoField(primary_key=True)
If you’d like to specify a custom primary key, specify
primary_key=True on one of your fields. If Django sees you’ve
explicitly set Field.primary_key, it won’t add the automatic id
column.
I have a django movie model
class Film(models.Model):
title = models.CharField(max_length=200)
movie_id = models.CharField(max_length=8, unique=True, primary_key=True)
director = models.ForeignKey('Director', on_delete=models.SET_NULL, null=True)
year = models.IntegerField(null=True)
genres = models.ManyToManyField(Genre)
I need to use movie_id as primary key, but also i need a field, which represents number of item's row in table.
It must increment automatically, just like standard "id" field.
How can i add it?
This question https://stackoverflow.com/users/3404040/take-care is similar, but i can't use my "number" field as primary key, because movie_id is already used for that.
You can use something like this, but it can be resource consuming if you do not want to use the default id field.
class Film(models.Model):
def number():
no = Film.objects.count()
return no + 1
movie_row = models.IntegerField(unique=True,default=number)
From Django's Documentation:
By default, Django gives each model the following field:
id = models.AutoField(primary_key=True)
This is an auto-incrementing primary key.
If you’d like to specify a custom primary key, just specify primary_key=True on one of your fields. If Django sees you’ve explicitly set Field.primary_key, it won’t add the automatic id column.
Each model requires exactly one field to have primary_key=True (either explicitly declared or automatically added).
If you want yours to explicitly be called movie_id you probably need something like:
class Film(models.Model):
movie_id = models.AutoField(primary_key=True)
I have two models:
class Amodel(models.Model):
name = models.CharField(max_length=8)
desc = models.CharField(max_length=256)
class Bmodel(models.Model):
name = models.CharField(max_length=8)
desc = models.CharField(max_length=256)
now I have another model:
class Cmodel(models.Model):
name = models.CharField(max_length=8)
f_model = models.ForeignKey(to='there I want to dynamic refers to Amodle or Bmodel when create the Cmodel instance')
I want the Cmodel's f_model is choosable when Create the Cmodel instance, whether this is possible?
This feature called generic relations. Here is the official documentation link generic-relations
By definition of foreign key you can not assign foreign key to one field with choices of model
A FOREIGN KEY is a key used to link two tables together.
A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table.
Instead you can proceed to create two fields as below:
class Cmodel(models.Model):
name = models.CharField(max_length=8)
f_a_model = models.ForeignKey(Amodel, blank=True, null=True, on_delete=models.CASCADE)
f_b_model = models.ForeignKey(Bmodel, blank=True, null=True, on_delete=models.CASCADE)
This way you can create two fields and you can keep it as null.
So If you wish to proceed for Cmodel instance with foreign key of a model you can add it to field f_a_model and keep f_b_model null and vice versa
You may follow example of using generic-relations from this link and the doc.
When you use generic relations you need to write your own custom field and method for serializer or form or anywhere you wish to user it.
The Model class are generated by the django inspectdb and i can see the Id field, this is converted from the Legacy tables, the table cant be altered here,
class workFlowTemplate(models.Model):
rev = models.IntegerField(null=True, blank=True)
revtype = models.IntegerField(null=True, blank=True)
**id = models.IntegerField(null=True, blank=True)**
name = models.CharField(max_length=255, blank=True,primary_key=False)
class Meta:
db_table = 'workflow_template'
the problem is when i try to run the django it throws error
CommandError: One or more models did not validate:
pHApp.workflowtemplate: "id": You can't use "id" as a field name, because each model automatically gets an "id" field if none of the fields have primary_key=True. You need to either remove/rename your "id" field or add primary_key=True to a field.
Note
the id is not primary key here in this case,
When i tries to change
id = models.IntegerField(null=True, blank=True,primary_key=False)
the Issue still remains the same, and same error is repeated again, how to avoid this Issue ?
A model must have a primary key, so you need specify a primary key field, like this:
my_primary_key = models.AutoField(primary_key=True)
id = models.IntegerField(null=True, blank=True)
then it won’t add the automatic id column and you will not receive this error.
Column id is adding by django by default, if you did not specified another field as PK.
In your case, you specified id as your field, but you did not specified what field should be a primary key.
Solution - set another field as primary key since you can not rename id