We've got a small problem with a Django project we're working on and our postgresql database.
The project we're working on is a site/db conversion from a PHP site to a django site. So we used inspect db to generate the models from the current PHP backend.
It gave us this and we added the primary_key and unique equals True:
class Company(models.Model):
companyid = models.IntegerField(primary_key=True,unique=True)
...
...
That didn't seem to be working when we finally got to saving a new Company entry. It would return a not-null constraint error, so we migrated to an AutoField like below:
class Company(models.Model):
companyid = models.AutoField(primary_key=True)
...
...
This saves the Company entry fine but the problem is when we do
result = form.save()
We can't do
result.pk or result.companyid
to get the newly given Primary Key in the database (yet we can see that it has been given a proper companyid in the database.
We are at a loss for what is happening. Any ideas or answers would be greatly appreciated, thanks!
I just ran into the same thing, but during a django upgrade of a project with a lot of history. What a pain...
Anyway, the problem seems to result from the way django's postgresql backend gets the primary key for a newly created object: it uses pg_get_serial_sequence to resolve the sequence for a table's primary key. In my case, the id column wasn't created with a serial type, but rather with an integer, which means that my sequence isn't properly connected to the table.column.
The following is based on a table with the create statement, you'll have to adjust your table names, columns and sequence names according to your situation:
CREATE TABLE "mike_test" (
"id" integer NOT NULL PRIMARY KEY,
"somefield" varchar(30) NOT NULL UNIQUE
);
The solution if you're using postgresql 8.3 or later is pretty easy:
ALTER SEQUENCE mike_test_id_seq OWNED BY mike_test.id;
If you're using 8.1 though, things are a little muckier. I recreated my column with the following (simplest) case:
ALTER TABLE mike_test ADD COLUMN temp_id serial NOT NULL;
UPDATE mike_test SET temp_id = id;
ALTER TABLE mike_test DROP COLUMN id;
ALTER TABLE mike_test ADD COLUMN id serial NOT NULL PRIMARY KEY;
UPDATE mike_test SET id = temp_id;
ALTER TABLE mike_test DROP COLUMN temp_id;
SELECT setval('mike_test_id_seq', (SELECT MAX(id) FROM mike_test));
If your column is involved in any other constraints, you'll have even more fun with it.
Related
I'm using Django 3.0.6
I'm adding ForeignKey and ManyToManyField to my models, but I've noticed that django creates the INDEX, but not the actual FOREIGN KEY constraints in the db.
I've tried to explicitly set db_constraint=True but as expected is useless, since it's True by default.
I've found so many answers explaining this, but only for very old Django versions, doing tricks for enabling it when it was otherwise disabled. Now instead it should just work out of the box. Couldn't find anything AT ALL regarding Django 3.
Code
class Token (models.Model):
owner = models.ForeignKey(Chiefdom, on_delete=models.CASCADE, db_constraint=True)
county = models.ManyToManyField(County, db_constraint=True)
amount = models.PositiveSmallIntegerField()
SQLite
CREATE TABLE IF NOT EXISTS Piece_token (
id integer PRIMARY KEY AUTOINCREMENT NOT NULL,
amount smallint unsigned NOT NULL,
owner_id integer NOT NULL
);
CREATE INDEX IF NOT EXISTS Piece_token_owner_id_d27c77f0 ON Piece_token (owner_id);
CREATE TABLE IF NOT EXISTS Piece_token_county (
id integer PRIMARY KEY AUTOINCREMENT NOT NULL,
token_id integer NOT NULL,
county_id integer NOT NULL
);
CREATE INDEX IF NOT EXISTS Piece_token_county_county_id_57802417 ON Piece_token_county (county_id);
CREATE INDEX IF NOT EXISTS Piece_token_county_token_id_e7798ae9 ON Piece_token_county (token_id);
CREATE UNIQUE INDEX IF NOT EXISTS Piece_token_county_token_id_county_id_b06b16cc_uniq ON Piece_token_county (token_id, county_id);
I have checked now with same version of Django and SQLite there are all foreign keys present
For example
SELECT * FROM pragma_foreign_key_list('auth_user_groups');
Note all foreign keys are deferred and checked from Django -> source
Is it possible to change primary key of many to many field from default to uuid?
Table is already populated. What is the best way for migration?
You can create a migration that executes raw queries, add a new field to the table in the middle then generate the new UUID.
After that, another set of queries to drop the constraints on ID, add the new constraints to the new UUID field, and lastly drop the old ID field.
https://docs.djangoproject.com/en/2.0/ref/migration-operations/#runsql
I'm reading django doc and see how django knows to do the update or insert method when calling save(). The doc says:
If the object’s primary key attribute is set to a value that evaluates to True (i.e. a value other than None or the empty string), Django executes an UPDATE.
If the object’s primary key attribute is not set or if the UPDATE didn’t update anything, Django executes an INSERT link.
But in practice, when I create a new instance of a Model and set its "id" property to a value that already exist in my database records. For example: I have a Model class named "User" and have a propery named "name".Just like below:
class User(model.Model):
name=model.CharField(max_length=100)
Then I create a new User and save it:
user = User(name="xxx")
user.save()
now in my database table, a record like id=1, name="xxx" exists.
Then I create a new User and just set the propery id=1:
newuser = User(id=1）
newuser.save()
not like the doc says.when I had this down.I checked out two records in my database table.One is id = 1 ,another is id=2
So, can anyone explain this to me? I'm confused.Thanks!
Because in newer version of django ( 1.5 > ), django does not check whether the id is in the database or not. So this could depend on the database. If the database report that this is duplicate, then it will update and if the database does not report it then it will insert. Check the doc -
In Django 1.5 and earlier, Django did a SELECT when the primary key
attribute was set. If the SELECT found a row, then Django did an
UPDATE, otherwise it did an INSERT. The old algorithm results in one
more query in the UPDATE case. There are some rare cases where the
database doesn’t report that a row was updated even if the database
contains a row for the object’s primary key value. An example is the
PostgreSQL ON UPDATE trigger which returns NULL. In such cases it is
possible to revert to the old algorithm by setting the select_on_save
option to True.
https://docs.djangoproject.com/en/1.8/ref/models/instances/#how-django-knows-to-update-vs-insert
But if you want this behavior, set select_on_save option to True.
You might wanna try force_update if that is required -
https://docs.djangoproject.com/en/1.8/ref/models/instances/#forcing-an-insert-or-update
I am trying to work with QSqlRelationalTableModel of QT. I am new to MySQL table relationship but still I tried and can't make it work properly in QT.
I can get the result from MySQL:
create table stu(idd int auto_increment primary key,stu_name varchar(60),stu_age int);
create table stuInfo(idd int auto_increment primary key,stu_city varchar(60),stu_sub varchar(100), foreign key(id) references stu(id));
select stu.stu_name,stuInfo.stu_city from stu inner join stuInfo on stu.id=stuInfo.id;
To retrieve data from MySQL :
select stu.stu_name,stuInfo.stu_city from stu inner join stuInfo on stu.id=stuInfo.id;
In QT I can't make it work. I am getting confused with setRelation() and QSqlRelation() . I am not exactly understanding that how I can execute the same query in QT, I tried it in various way but sometime I get blank data, ugly header, errors etc.
Here is my learning code:
model = new QSqlRelationalTableModel();
model->setTable("stu");
model->setRelation(0,QSqlRelation("stu","id","stu_name","stu_age"));
model->setRelation(0,QSqlRelation("stuInfo","id","stu_city","stu_sub"));
model->select();
ui->tableView->setModel(model);
A QSqlRelation replaces the value of a field by the value of the other field in the relation, the replaced field won't appear in the query anymore, so you can't have 2 relations assigned to the same column, and you can't assign a relation to the primary key (as stated in the documentation of setRelation).
Basically the structure for which QSqlRelationalTableModel should be used would be a main table which would have 1 or more foreign index fields, and each of these fields could be replaced by the value of a chosen field in the tables from which the foreign indexes comes from (e.g.: to replace a "city_id" numerical field in the main table by the name of the city coming from another table for which that "city_id" is the primary key).
For what you want to do, you should use QSqlQueryModel with a manually constructed query instead of QSqlRelationalTableModel.
The problem is that your code does not really express the model you described.
You have a primary table called stuInfo, which references another table called stu.
To do this in Qt, you should create a table based on "stuInfo" (and not "stu"!):
model=new QSqlRelationalTableModel();
model->setTable("stuInfo");
Then you can implement your foreign key, as a relation:
model->setRelation(3,QSqlRelation("stu","id","stu_name"));
You need to point to index "3", which is the position of the reference field "id", on stuInfo table (0 will point to the primary key, which is not what you want!). The parameters of the QsqlRelation are the reference table name ("stu") the primary field name ("id") and the reference table field to which you want to point: in this case I am pointing to "stu_name"; if I wanted to point to the age, I could do something like this instead:
model->setRelation(3,QSqlRelation("stu","id","stu_age"));
After this code:
model->select();
ui->tableView->setModel(model);
you should have a view that shows you all the fields on stuInfo, and whose last field ("id") is mapped to the name (or age) on the "stu" table;
I created the models in a Django app using manage.py inspectdb on an
existing postgres database. This seemed to work except that all the
primary keys were described in the models as IntegerFields, which made
them editable in the admin panel, and had to be hand-entered based on
knowledge of the id of the previous record. I just learned about this
after some usage by the client, so I went back to change things like
blog_id = models.IntegerField(primary_key=True)
...to...
blog_id = models.AutoField(primary_key=True)
Now the id fields don't appear in the admin panel (good), but adding new rows
has become impossible (not good).
IntegrityError at /admin/franklins_app/blog/add/
duplicate key value violates unique constraint "blog_pkey"
What's the fix? (Bonus question: is it possible to capture the value that Django is trying to assign as the primary key for the new row?)
The sequence behind the serial field which is your primary key doesn't know about the manually entered records.
Find the maximum value of the primary key:
SELECT MAX(<primary_key>) FROM <your_table>;
Then set the next value of the underlying sequence to a number greater than that:
SELECT SETVAL('<primary_key_seq>', <max_value_in_primary_key_plus_something_for_safety>);
You'll find the name of the sequence (mentioned above as <primary_key_seq>) using:
SELECT pg_get_serial_sequence('<your_table_name>', '<primary_key_column_name');