i'm using djangorestframework. the models one meeting could have many participates.
So i tried to use ManytoManyField of django:
class Meeting(models.Model):
name=models.CharField(max_length=100)
participates=models.ManyToManyField(Person)
by python manager.py sqlall XXX the DB tables are:
CREATE TABLE "OA_meeting_participates" (
"id" integer NOT NULL PRIMARY KEY,
"meeting_id" integer NOT NULL,
"person_id" integer NOT NULL REFERENCES "OA_person" ("id"),
UNIQUE ("meeting_id", "person_id")
)
;
CREATE TABLE "OA_meeting" (
"id" integer NOT NULL PRIMARY KEY,
"name" varchar(100) NOT NULL,
)
the problems comes: when i create a meeting by selecting some persons, server response 'participates' is an invalid keyword argument for this function.
since OA_meeting does not have participates field.
so how to solve it?
see the docs on manytomany fields. You need to create the meeting and person objects separately first, and then do meeting.partcipates.add(person)
(btw, i think the word you are looking for is participANts)
Related
This is the relation I want to create for my quiz app and im using python
Module:
c.execute("""CREATE TABLE Questions (
mod_id INTEGER PRIMARY KEY,
mod_name TEXT NOT NULL
)""")
Question:
c.execute("""CREATE TABLE Questions (
quest_id INTEGER PRIMARY KEY,
quest_name TEXT NOT NULL,
mod_id INTEGER NOT NULL,
FOREIGN KEY (mod_id)
REFERENCES Modules (mod_id)
)""")
Now Since the each feedback correspont to 1 question, how do i sort of create one to one relationship? should I do the same as I did for the question table? would this be handle automatically by sqlite3??
Appreciate all sort of help Thanks!!!
EDIT: Does my feedback table need to have a primary key?? I think no because when accesing the feeback table to delete or add data we just pass the question ID as the parameter to look that row up.
I want to save data from the Django model to PostgreSQL database with:
mymodel.objects.create(title='test')
this model only has title and id but it raises this error:
django.db.utils.IntegrityError: null value in column "id" violates not-null constraint
how can I fix it? why id is not set automatically as always?
If you somehow had your ID field altered on the database level and you want to make it an autoincrementing sequence again do this
In the below example check what mymodel's table will be in Postgres in the example below its called mytable
// Pick a starting value for the serial, greater than any existing value in the table
SELECT MAX(id)+1 FROM mytable
// Create a sequence for the serial (tablename_columnname_seq is a good name)
CREATE SEQUENCE mytable_id_seq MINVALUE 3 (assuming you want to start at 3)
// Alter the default of the column to use the sequence
ALTER TABLE test ALTER id SET DEFAULT nextval('mytable_id_seq')
// Alter the sequence to be owned by the table/column;
ALTER SEQUENCE mytable_id_seq OWNED BY mytable.id
REF: Changing primary key int type to serial
You should allow Django to create the id as the primary key instead of explicitly putting it in your model. You could call it something else like mymodel_id if you need it as a separate field.
Example:
class Book(models.Model):
title = models.CharField(null=False, blank=False)
def __str__(self):
return str(self.id)
After that run:
python manage.py makemigrations
python manage.py migrate
If you need to integrate Django with an existing database you can try this: Integrating Django with an existing database
I've finished making some SQLite tables and am executing the instructions. When executing the instructions, the following error has come up:
sqlite3.OperationalError: near "Category": syntax error
Most of my tables use the same sort of format, below is an example of one such table.
CategoryTableSQL = """ CREATE TABLE IF NOT EXISTS Category(
CategoryID integer PRIMARY KEY AUTOINCREMENT
Category text NOT NULL
);"""
databaseNewTable(Connection, CategoryTableSQL)
You forgot a comma between the declaration of your table fields in your SQL-statement: It should be like this. Always use comma's to seperate the field-creation statements. Except of course, for the last field you create =). Also, I would take care in naming your fields the same name as your tables. To prevent confusion. Just my two cents
CREATE TABLE IF NOT EXISTS Category(
CategoryID integer PRIMARY KEY AUTOINCREMENT,
Category text NOT NULL
);
I think, You just need to add the ',' symbol after the AUTOINCREMENT word. :-)
Like this:
CategoryTableSQL = """ CREATE TABLE IF NOT EXISTS Category(
CategoryID integer PRIMARY KEY AUTOINCREMENT,
Category text NOT NULL
);"""
databaseNewTable(Connection, CategoryTableSQL)
We have Django Model, use Binary Field for ID.
# Create your models here.
class Company(models.Model):
id = models.BinaryField(max_length=16, primary_key=True)
name = models.CharField(max_length=12)
class Meta:
db_table = "company"
We use MySQL Database and have error when migrate.
File "/home/cuongtran/Downloads/sample/venv/lib/python3.5/site-packages/MySQLdb/connections.py", line 270, in query
_mysql.connection.query(self, query)
django.db.utils.OperationalError: (1170, "BLOB/TEXT column 'id' used in key specification without a key length")
Do you have any solution? We need to use MySQL and want to use the Binary Field for ID.
Thank you!
I think you cannot achieve this. Based on Django documentation it looks like use of binary fields is discouraged
A field to store raw binary data. It only supports bytes assignment.
Be aware that this field has limited functionality. For example, it is
not possible to filter a queryset on a BinaryField value. It is also
not possible to include a BinaryField in a ModelForm.
Abusing BinaryField
Although you might think about storing files in the database, consider
that it is bad design in 99% of the cases. This field is not a
replacement for proper static files handling.
And based on a Django bug, it is most likely impossible to achieve a unique value restriction on a binary field. This bug is marked as wont-fix. I am saying most likely impossible as I did not find evidence to confirm that binary field is stored as a BLOB field but the error does allude to it.
Description
When I used a field like this:
text = models.TextField(maxlength=2048, unique=True)
it results in the following sql error when the admin app goes to make the table
_mysql_exceptions.OperationalError: (1170, "BLOB/TEXT column 'text' used in key specification without a key length")
After a bit of investigation, it turns out that mysql refuses to use unique with the column unless it is only for an indexed part of the text field:
CREATE TABLE `quotes` ( \`id\` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `text` longtext NOT NULL , \`submitTS\` datetime NOT NULL, `submitIP` char(15) NOT NULL, `approved` bool NOT NULL, unique (text(1000)));
Of course 1000 is just an arbitrary number I chose, it happens to be the maximum my database would allow. Not entirely sure how this can be fixed, but I figured it was worth mentioning.
MySQL restricts the primary key on BLOB/TEXT column to first N chars, when you generates migration file using Django's makemigrations command, BinaryField in Django is mapped to longblob which is BLOB column in MySQL without specifying the key length.
Which means your Django model definition :
class Company(models.Model):
id = models.BinaryField(max_length=16, primary_key=True)
name = models.CharField(max_length=12)
class Meta:
db_table = "company"
will be converted to SQL expression that causes this error (You can check out the detailed SQL expressions by sqlmigrate command) :
CREATE TABLE `company` (`id` longblob NOT NULL PRIMARY KEY,
`name` varchar(12) NOT NULL);
while the correct SQL expression for MySQL should be like this :
CREATE TABLE `company` (`id` longblob NOT NULL,
`name` varchar(12) NOT NULL);
ALTER TABLE `company` ADD PRIMARY KEY (id(16));
where PRIMARY KEY (id(16)) comes from your id length in the BLOB column, used to structure primary key index of the table.
So the easiest solution is as described in the accepted answer -- avoid BinaryField in Django as primary key, or you can manually add raw SQL scripts to your migration file if you really need BinaryField (BLOB column) to be primary key and you are sure the id field will NOT go beyond the specific size (in your case, 16 bytes).
So, here's my model:
class MyModel(models.Model):
timestamp = models.DateTimeField(primary_key=True)
fielda = models.TextField()
When I call syncdb, django doesn't add a constraint to postgresql for timestamp to be unique, even though it gives it the primary key constraint.
If I change timestamp to just unique=True, django creates the unique constraint. However, if I combine unique=True and primary_key=True, django doesn't create the unique constraint.
My info:
django-south v1.8
django 1.4
python 2.7
postgresql 9.1
Edit:
If I save a model with the same exact timestamp twice in two different runs (not the same process), it doesn't raise and IntegrityError like it should. But when it creates the unique constraint and no primary key, it does with the same code.
Edit 2:
This is the code that runs when I have CONSTRAINT "MyModel_pkey" PRIMARY KEY ("timestamp") in postgresql from just having timestamp = models.DateTimeField(primary_key=True)
timestamp = datetime.datetime(2013, 7, 31, 0, 0, 0).replace(tzinfo=utc)
print timestamp # prints 2013-07-31 00:00:00+00:00
row = MyModel(timestamp=timestamp, fielda='test')
row.save()
When run twice in a row, it doesn't raise an IntegrityError. However, with the unique=True and not primary_key=True, it does raise an IntegrityError.
Maybe the example from the docs can bring some light into your question
Technically, a primary key constraint is simply a combination of a
unique constraint and a not-null constraint. So, the following two
table definitions accept the same data:
CREATE TABLE products (
product_no integer UNIQUE NOT NULL,
name text,
price numeric );
CREATE TABLE products (
product_no integer PRIMARY KEY,
name text,
price numeric );
[...] A primary key indicates that a column or group of columns can be
used as a unique identifier for rows in the table [...] Adding a
primary key will automatically create a unique btree index on the
column or group of columns used in the primary key. [...]
Ricola3D linked me to the same question (that's answered) that explains my problem.
Answered Question