CODEWITHSUNDEEP
pythondjangojsonexport
Nathan Osman
Nathan Osman

Reputation: 73195

Why am I getting an IntegrityError when attempting to import JSON?

I am trying to export some data from a MySQL database and import it into a PostgreSQL database. The two models are described below:

class Location(models.Model):
    name = models.CharField(max_length=100)

class Item(models.Model):
    title    = models.CharField(max_length=200)
    location = models.ForeignKey(Location)

class Book(Item):
    author = models.CharField(max_length=100)

Notice that the Book model inherits from the Item model. (Also, I do realize that author really should be a separate model - but I need something simple to demonstrate the problem.) I first attempt to export the data from the model using the dumpdata command:

./manage.py dumpdata myapp.location >locations.json
./manage.py dumpdata myapp.item >items.json
./manage.py dumpdata myapp.book >books.json

The JSON in items.json looks something like this:

{
    "fields": {
        "title": "Introduction to Programming",
        "location": 1
    },
    "model": "myapp.item",
    "pk": 1
}

The JSON in books.json looks something like this:

{
    "fields": {
        "author": "Smith, Bob"
    },
    "model": "myapp.book",
    "pk": 1
}

I can import locations.json and items.json without issue but as soon as I attempt to import books.json, I run into the following error:

IntegrityError: Problem installing fixture 'books.json': Could not load
  myapp.Book(pk=1): null value in column "location_id" violates not-null
  constraint

Edit: the schema for myapp.books (according to PostgreSQL itself) is as follows:

# SELECT * FROM myapp_book;
 item_ptr_id | author
-------------+--------
(0 rows)

Upvotes: 2

Views: 471

Answers (2)

Density 21.5
Density 21.5

Reputation: 1930

The books.json file needs to have all the fields of the parent model, in your case 'title' and 'location' fields (and appropriate values of course) need to be added (from the items.json file). loaddata doesn't use the database structure (with intermediate the table and all), but the checks the actual fields of the model.

To avoid ending up with double entries, you will also have to remove all the json entries in the items.json file that are pointed to by the original mysql database in the myapp_book table.

Another solution would be to use http://pypi.python.org/pypi/py-mysql2pgsql (see also this question)

Upvotes: 1

Daniel Roseman
Daniel Roseman

Reputation: 599630

Seems like for whatever reason the Books schema in your postgres db doesn't match the models - it has a location_id column. You should drop the table and rerun syncdb.

Upvotes: 0

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