    print TestModel.objects.filter(manytomany=None)



Adding to @Bernhard answer, other possible solution can be achieved using the `Q()` object.

    from django.db.models import Q
    
    filters = Q(manytomany=None)
    
    TestModel.objects.filter(filters)

**Negation:** 

    filters = ~Q(manytomany=None)
    
    TestModel.objects.filter(filters)



Even though the topic has already an answer this could be of help. Try with lookups:

    empty = TestModel.objects.filter(manytomany__isnull = True)
    #........If you want to get their counter part
    not_empty = TestModel.objects.filter(manytomany__isnull = False)

Basically, you get two query sets: one where your manytomany fields are empty, and the other with objects that have data in the manytomanyfield.

Hope this could be of some help!

Is this a good way to check if the value of a field is `null`?

    if($(&#39;#person_data[document_type]&#39;).value() != &#39;NULL&#39;){}

Or is there a better way?

jQuery: checking if the value of a field is null (empty)

I&#39;m working with some CSV files, with the following code:

    reader = csv.reader(open(filepath, &quot;rU&quot;))
    try:
        for row in reader:
            print &#39;Row read successfully!&#39;, row
    except csv.Error, e:
        sys.exit(&#39;file %s, line %d: %s&#39; % (filename, reader.line_num, e))

And one file is throwing this error: 

    file my.csv, line 1: line contains NULL byte

What can I do? Google seems to suggest that it may be an Excel file that&#39;s been saved as a .csv improperly. Is there any way I can get round this problem in Python?

== UPDATE ==

Following @JohnMachin&#39;s comment below, I tried adding these lines to my script: 

    print repr(open(filepath, &#39;rb&#39;).read(200)) # dump 1st 200 bytes of file
    data = open(filepath, &#39;rb&#39;).read()
    print data.find(&#39;\x00&#39;)
    print data.count(&#39;\x00&#39;)

And this is the output I got: 
   

    &#39;\xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1\x00\x00\x00\x00\x00\x00\x00\x00\ .... &lt;snip&gt;
    8
    13834

So the file does indeed contain NUL bytes. 

Python CSV error: line contains NULL byte

In Django is there a way to filter on a manytomany field being empty or null.

    class TestModel(models.Model):
        name = models.CharField(_(&#39;set name&#39;), max_length=200)
        manytomany = models.ManyToManyField(&#39;AnotherModel&#39;, blank=True, null=True)
    
    print TestModel.objects.filter(manytomany__is_null=True)

 


django - query filter on manytomany is empty

In Django is there a way to filter on a manytomany field being empty or null.
<pre><code class="hljs language-ini">class TestModel(models.Model):
 name = models.CharField(_('set name'), max_length=200)
 manytomany = models.ManyToManyField('AnotherModel', blank=True, null=True)

print TestModel.objects.filter(manytomany__is_null=True)
</code></pre>

Is there any way to use Socket.IO http://socket.io/ with Django?

Can I use Socket.IO with Django?

Suppose I have a simple model class like this:

    class TestModel(models.Model):
        testkey = models.ForeignKey(TestModel2)
        ...

When I am creating a TestModel object I have to pass to it an instance of the TestModel2 object to create it:

    testkey =TestModel2.objects.get(id=...)
    TestModel.objects.create(testkey=testkey)

This results in 2 queries to database I suppose, and I have a list of Foreign key IDs that I need to create objects with.

Is it possible to create objects with foreign keys without initially retrieving the foreign key objects?

Django model object with foreign key creation

I have a model called `Thing` with an attribute called `name`, and I want name to be a char field that&#39;s _only_ 3 characters long.

How do I write a test for that?

    class TestCase1(TestCase):
        def test1(self):
            thing = Thing(name=&#39;1234&#39;)

that test should fail. How do I properly write the test so that the test _passes_ when that object fails?




how to write django test meant to fail?

The table in question contains roughly ten million rows.

    for event in Event.objects.all():
        print event

This causes memory usage to increase steadily to 4 GB or so, at which point the rows print rapidly. The lengthy delay before the first row printed surprised me – I expected it to print almost instantly.

I also tried `Event.objects.iterator()` which behaved the same way.

I don&#39;t understand what Django is loading into memory or why it is doing this. I expected Django to iterate through the results at the database level, which&#39;d mean the results would be printed at roughly a constant rate (rather than all at once after a lengthy wait).

What have I misunderstood?

(I don&#39;t know whether it&#39;s relevant, but I&#39;m using PostgreSQL.)

Why is iterating through a large Django QuerySet consuming massive amounts of memory?

How do I check if a variable is **False** using Django template syntax?

    {% if myvar == False %}

Doesn&#39;t seem to work.

Note that I very specifically want to check if it has the Python value `False`. This variable could be an empty array too, which is *not* what I want to check for.

Django templates: If false?

I have two questions:

1. How do I delete a table in Django?
2. How do I remove all the data in the table?

This is my code, which is not successful:

    Reporter.objects.delete()




How to remove all of the data in a table using Django

I&#39;ve got a field in one model like:

    class Sample(models.Model):
        date = fields.DateField(auto_now=False)

Now, I need to filter the objects by a date range.

How do I filter all the objects that have a date between `1-Jan-2011` and `31-Jan-2011`?

How do I filter query objects by date range in Django?

When I do this,

    &gt;&gt;&gt; b = Blog.objects.all()
    &gt;&gt;&gt; b

I get this:

    &gt;&gt;&gt;[&lt;Blog: Blog Title&gt;,&lt;Blog: Blog Tile&gt;]

When I query what type `b` is,

    &gt;&gt;&gt; type(b)

I get this:

    &gt;&gt;&gt; &lt;class &#39;django.db.models.query.QuerySet&#39;&gt;

What does this mean? Is it a data type like `dict`, `list`, etc?

An example of how I can build data structure like a `QuerySet` will be appreciated.

I would want to know how Django builds that `QuerySet` (the gory details).


What is a Django QuerySet?

I have the following Django model:

    class Make:
       name = models.CharField(max_length=200)
    
    class MakeContent:
       make = models.ForeignKey(Make)
       published = models.BooleanField()

I&#39;d like to know if it&#39;s possible (without writing SQL directly) for me to generate a queryset that contains all `Make`s and each one&#39;s related `MakeContent`s where `published = True`.


Django Queryset with filtering on reverse foreign key

How can I add a field for the count of objects in a database. I have the following models:

    class Item(models.Model):
        name = models.CharField()

    class Contest(models.Model);
        name = models.CharField()

    class Votes(models.Model):
        user = models.ForeignKey(User)
        item = models.ForeignKey(Item)
        contest = models.ForeignKey(Contest)
        comment = models.TextField()

To find the votes for contestA I am using the following query in my view

    current_vote = Item.objects.filter(votes__contest=contestA)

This returns a queryset with all of the votes individually but I want to get the count votes for each item, anyone know how I can do that? thanks

Content Type	Original Author	Original Content on Stackoverflow
Question	John	View Question on Stackoverflow
Solution 1 - Django	Bernhard Vallant	View Answer on Stackoverflow
Solution 2 - Django	Rakmo	View Answer on Stackoverflow
Solution 3 - Django	Firingam	View Answer on Stackoverflow

django - query filter on manytomany is empty

Django Problem Overview

Django Solutions

Solution 1 - Django

Solution 2 - Django

Solution 3 - Django

Python CSV error: line contains NULL byte

jQuery: checking if the value of a field is null (empty)

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