ManyToManyRel is used by the ManyToManyField to implement the relationship object for the Field base class which it extends. If you were to create a new field class that extended the Field class and contained a many-to-many relationship you might find this class convenient but it should not be used in your models (which is where you will see the pop-up suggestion if your editor lists available calls).

See class Field @:
&lt;https://github.com/django/django/blob/master/django/db/models/fields/__init__.py&gt;
class ManyToManyRel &amp; class ManyToManyField @:
&lt;https://github.com/django/django/blob/master/django/db/models/fields/related.py&gt;

*I am glad that the vast majority of the questions here are questions that can be answered by looking at reference material and documentation. Researching and sharing ideas and digging into code that is &quot;not for external use&quot; is the fun. I know how to start answering this question, if i didn&#39;t i would not have written anything. Good question dude!*


If you discovered ManyToManyRel by digging into the source code, you can read the docstrings for the class. It&#39;s not documented anywhere - on purpose, because it&#39;s not for external use. It is certainly not meant for defining actual field relationships between models.

    NSDictionary* fileAttributes = 
        [[NSFileManager defaultManager] attributesOfItemAtPath:filename 
                                                         error:nil]

From the file attribute keys, you can get the date, size, etc. But how do you get the duration?

How to get the duration of an audio file in iOS?

How can I right-align an image using CSS.

I **do not** want the text to `wrap-around` the image. I want the right aligned image to be on a line by itself.

right align an image using CSS HTML

What is the difference between Django&#39;s `models.ManyToManyField` and `models.ManyToManyRel`? I&#39;m confused about this stuff.


Django: what is the difference (rel &amp; field)

<p>What is the difference between Django's <code>models.ManyToManyField</code> and <code>models.ManyToManyRel</code>? I'm confused about this stuff.</p>


I am pretty sure there is a common idiom, but I couldn&#39;t find it with Google Search... 

Here is what I want to do (in Java):

&lt;!-- language: lang-java --&gt;

    // Applies the predicate to all elements of the iterable, and returns
    // true if all evaluated to true, otherwise false
    boolean allTrue = Iterables.all(someIterable, somePredicate);

How is this done &quot;Pythonic&quot; in Python?

Also would be great if I can get answer for this as well:

&lt;!-- language: lang-java --&gt;

    // Returns true if any of the elements return true for the predicate
    boolean anyTrue = Iterables.any(someIterable, somePredicate);


Check if a predicate evaluates true for all elements in an iterable in Python

I&#39;ve read almost all the other questions about the topic, but my code still doesn&#39;t work.

I think I&#39;m missing something about python variable scope.

Here is my code:

    PRICE_RANGES = {
                    64:(25, 0.35),
                    32:(13, 0.40),
                    16:(7, 0.45),
                    8:(4, 0.5)
                    }
    
    def get_order_total(quantity):
        global PRICE_RANGES
        _total = 0
        _i = PRICE_RANGES.iterkeys()
        def recurse(_i):
            try:
                key = _i.next()
                if quantity % key != quantity:
                    _total += PRICE_RANGES[key][0]
                return recurse(_i) 
            except StopIteration:
                return (key, quantity % key)
        
        res = recurse(_i)

And I get 

&gt; &quot;global name &#39;_total&#39; is not defined&quot;

I know the problem is on the `_total` assignment, but I can&#39;t understand why.
Shouldn&#39;t `recurse()` have access to the parent function&#39;s variables?

Can someone explain to me what I&#39;m missing about python variable scope?

Python nested functions variable scoping

I am trying to install version 1.2.2 of `MySQL_python`, using a fresh virtualenv created with the `--no-site-packages` option. The current version shown in PyPi is [1.2.3][1]. Is there a way to install the older version? I have tried:

```bash
pip install MySQL_python==1.2.2
```

However, when installed, it still shows `MySQL_python-1.2.3-py2.6.egg-info` in the site packages. Is this a problem specific to this package, or am I doing something wrong?

  [1]: http://pypi.python.org/pypi/MySQL-python/1.2.3

Installing specific package version with pip

I need to setup environment with the path to a binary. In the shell, I can use `which` to find the path. Is there an equivalent in python?
This is my code.

&lt;!-- language: python --&gt;

    cmd = [&quot;which&quot;,&quot;abc&quot;]
    p = subprocess.Popen(cmd, stdout=subprocess.PIPE)
    res = p.stdout.readlines()
    if len(res) == 0: return False
    return True

How can I find the path for an executable?

Why does Python not support a record type natively? It&#39;s a matter of having a mutable version of namedtuple.

I could use `namedtuple._replace`. But I need to have these records in a collection and since `namedtuple._replace` creates another instance, I also need to modify the collection which becomes messy quickly. 

Background:
I have a device whose attributes I need to get by polling it over TCP/IP. i.e. its representation is a mutable object.

Edit:
I have a set of devices for whom I need to poll.

Edit:
I need to iterate through the object displaying its attributes using PyQt. I know I can add special methods like `__getitem__` and `__iter__`, but I want to know if there is an easier way.

Edit:
I would prefer a type whose attribute are fixed (just like they are in my device), but are mutable.

Why does Python not support record type? (i.e. mutable namedtuple)

We have a Django application that requires a specific level of password complexity. We currently enforce this via client-side JavaScript which can easily be defeated by someone who is appropriately motivated.

I cannot seem to find any specific information about setting up server-side password strength validation using the django contrib built in views. Before I go about re-inventing the wheel, is there a proper way to handle this requirement?



Enforcing password strength requirements with django.contrib.auth.views.password_change

Django has `truncatewords` template tag, which cuts the text at the given word count. But there is nothing like *truncatechars*.

What&#39;s the best way to cut the text in the template at given char-length limit?

Django template tag to truncate text

I am using a simple unit test based test runner to test my Django application.

My application itself is configured to use a basic logger in settings.py using:

    logging.basicConfig(level=logging.DEBUG)

And in my application code using:

    logger = logging.getLogger(__name__)
    logger.setLevel(getattr(settings, &#39;LOG_LEVEL&#39;, logging.DEBUG))

However, when running unittests, I&#39;d like to disable logging so that it doesn&#39;t clutter my test result output. Is there a simple way to turn off logging in a global way, so that the application specific loggers aren&#39;t writing stuff out to the console when I run tests?


How can I disable logging while running unit tests in Python Django?

Just wondering where I can set the url to redirect to after logout. I know you can set the login url. I want to redirect to my home page.

How to configure where to redirect after a log out in Django?

I have a Django Form class defined likes this in `Models`:

    class AccountDetailsForm(forms.Form):
        ...
        adminuser = forms.ModelChoiceField(queryset=User.objects.all())

This works OK, but it has some limitations I can&#39;t seem to work around:

(1) I would like to use a filter on the queryset, based on a variable `accountid` passed to the form, like this:

    User.objects.filter(account=accountid)

This can&#39;t work in the model because `accountid` can&#39;t be passed as a variable, of course.

It follows that the `queryset` must somehow be defined in the `Views`, but as far as I can see it&#39;s a required field in the Form class.

(2) I would like to make the default choice of `AccountDetailsForm` an object in the database, which I can select in the `Views` like this:

    User.objects.filter(account=accountid).filter(primary_user=1)

I&#39;ve tried specifying the adminuser as a default value in the form, (which works with other standard form fields, like `CharField`):

    adminuser = User.objects.filter(account=accountid).filter(primary_user=1)

    ...
    
    form = AccountDetailsForm({&#39;adminuser&#39;: adminuser})
    return render_to_response(&#39;accounts/edit/accountdetails.html&#39;, 
    {&#39;form&#39;: form, &#39;account&#39;:account})

But no luck.

Should I be using something other than `ModelChoiceField` given the flexibility I need here?

Thanks.

Django ModelChoiceField: filtering query set and setting default value as an object

Is it using some kind of byte codes modification to the original classes?

Or, maybe Hibernate get the dirty state by compare the given object with previously persisted version?

I&#39;m having a problem with `hashCode()` and `equals()` methods for complicated objects. I feel it would be very slow to compute hash code if the object has collection members, and cyclic references are also a problem.

If Hibernate won&#39;t use `hashCode()`/`equals()` to check the dirty state, I guess I should not use `equals()`/`hashCode()` for the entity object (not value object), but I&#39;m also afraid if the same operator (`==`) is not enough.

So, the questions are:

1. How does Hibernate know if a property of an object is changed?

2. Do you suggest to override the `hashCode()`/`equals()` methods for complicated objects? What if they contains cyclic references?

    And, also, 

3. Would `hashCode()`/`equals()` with only the `id` field be enough?


How does Hibernate detect dirty state of an entity object?

Imagine you have two entities, **Player** and **Team**, where players can be on multiple teams.  In my data model, I have a table for each entity, and a join table to maintain the relationships. [Hibernate][1] is fine at handling this, but how might I expose this relationship in a [RESTful][2] API?

I can think of a couple of ways.  First, I might have each entity contain a list of the other, so a Player object would have a list of Teams it belongs to, and each Team object would have a list of Players that belong to it.  So to add a Player to a Team, you would just [POST][3] the player&#39;s representation to an endpoint, something like POST `/player` or POST `/team` with the appropriate object as the payload of the request.  This seems the most &quot;RESTful&quot; to me, but feels a little weird.

    /api/team/0:

    {
        name: &#39;Boston Celtics&#39;,
        logo: &#39;/img/Celtics.png&#39;,
        players: [
            &#39;/api/player/20&#39;,
            &#39;/api/player/5&#39;,
            &#39;/api/player/34&#39;
        ]
    }

    /api/player/20:

    {
        pk: 20,
        name: &#39;Ray Allen&#39;,
        birth: &#39;1975-07-20T02:00:00Z&#39;,
        team: &#39;/api/team/0&#39;
    }

The other way I can think of to do this would be to expose the relationship as a resource in its own right.  So to see a list of all the players on a given team, you might do a GET `/playerteam/team/{id}` or something like that and get back a list of PlayerTeam entities.  To add a player to a team, POST `/playerteam` with an appropriately built PlayerTeam entity as the payload.

    /api/team/0:

    {
        name: &#39;Boston Celtics&#39;,
        logo: &#39;/img/Celtics.png&#39;
    }

    /api/player/20:

    {
        pk: 20,
        name: &#39;Ray Allen&#39;,
        birth: &#39;1975-07-20T02:00:00Z&#39;,
        team: &#39;/api/team/0&#39;
    }

    /api/player/team/0/:

    [
        &#39;/api/player/20&#39;,
        &#39;/api/player/5&#39;,
        &#39;/api/player/34&#39;
    ]

What is the best practice for this?

  [1]: https://en.wikipedia.org/wiki/Hibernate_%28Java%29
  [2]: https://en.wikipedia.org/wiki/Representational_state_transfer#RESTful_web_services
  [3]: https://en.wikipedia.org/wiki/POST_%28HTTP%29




How can I handle many-to-many relationships in a RESTful API?

I want to use Oracle SQL Developer to generate an ER diagram for my DB tables but I am new to Oracle and this tool.

What is the process for creating an ER diagram in SQL Developer?

How to generate an entity-relationship (ER) diagram using Oracle SQL Developer

Someone told me that it was bad design to have loops in the datamodel. I have heard this before a couple of times but didn&#39;t pay much attention. For example you have entities User, Project, Activity. A project is owned by a User, so we have a one-to-many relationship from user to Project. An activity can be assigned to a single User, another one-to-many relationship from User to Activity. Of course a project is defined by a set of activities, another one-to-many relationship from Project to Activity. Thus a loop is formed.

I asked this guy why is it bad design but he told me he didn&#39;t know either, he was told so too, monkey learning at it&#39;s best.

I tried searching but I guess I didn&#39;t use the proper words, however this seems  to me something that should be fundamental for someone trying to design a DB.

So, can anyone point me to some useful info about loops/cycles in er/db diagrams, should they be avoided?






Why should I avoid loops when designing relationships for a database?

Is there any way to get an ER model of a database from the server that is connected to my MySQL Workbench?

Content Type	Original Author	Original Content on Stackoverflow
Question	sultan	View Question on Stackoverflow
Solution 1 - Python	Damon	View Answer on Stackoverflow
Solution 2 - Python	Daniel Roseman	View Answer on Stackoverflow

Django: what is the difference (rel & field)

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

right align an image using CSS HTML

How to get the duration of an audio file in iOS?

Attributions