    ./manage.py migrate myapp zero

See: https://docs.djangoproject.com/en/1.9/ref/django-admin/#migrate

In Django 1.11: https://docs.djangoproject.com/en/1.11/ref/django-admin/#migrate

I need to get column names and their tables in a SQLite database. What I need is a resultset with 2 columns: `table_name | column_name`. 

In MySQL, I&#39;m able to get this information with a SQL query on database `INFORMATION_SCHEMA`. However the SQLite offers table `sqlite_master`: 

    sqlite&gt; create table students (id INTEGER, name TEXT);
    sqlite&gt; select * from sqlite_master;
      table|students|students|2|CREATE TABLE students (id INTEGER, name TEXT)


which results a DDL construction query (`CREATE TABLE`) which is not helpful for me and I need to parse this to get relevant information. 

I need to get list of tables and join them with columns or just get columns along with table name column. So `PRAGMA table_info(TABLENAME)` is not working for me since I don&#39;t have table name. I want to get all column metadata in the database.

Is there a better way to get that information as a result set by querying database?

SQLite Schema Information Metadata

&gt; **Possible Duplicates:**  
&gt; [Why would someone use #define to define constants?](https://stackoverflow.com/questions/6274008/why-would-someone-use-define-to-define-constants)  
&gt; [difference between a macro and a const in c++](https://stackoverflow.com/questions/6393776/difference-between-a-macro-and-a-const-in-c)  
&gt; [C++ - enum vs. const vs. #define](https://stackoverflow.com/questions/4767667/c-enum-vs-const-vs-define)  

&lt;!-- End of automatically inserted text --&gt;

What is the difference between using `#define` and `const` for creating a constant? Does any have a performance advantage over the other? Naturally I prefer using the `const` but I&#39;m going to consider the `#define` if it has suitable advantages.    


What is the difference between #define and const?

Can you migrate an app backwards to before its first migration in Django South? If not, are there plans to add such functionality, perhaps using an option passed to `migrate`?

Can you migrate backwards to before the first migration in South?

<p>Can you migrate an app backwards to before its first migration in Django South? If not, are there plans to add such functionality, perhaps using an option passed to <code>migrate</code>?</p>


    class TodoList(models.Model):
        title = models.CharField(maxlength=100)
        slug = models.SlugField(maxlength=100)
        def save(self):
            self.slug = title
            super(TodoList, self).save()

I&#39;m assuming the above is how to create and store a slug when a title is inserted into the table TodoList, if not, please correct me!

Anyhow, I&#39;ve been looking into pre_save() as another way to do this, but can&#39;t figure out how it works.  How do you do it with pre_save()?

is it like

    def pre_save(self):
         self.slug = title

I&#39;m guessing no.  What is the code to do this?

Thanks!

Populating django field with pre_save()?

I came across this:

    &gt;&gt;&gt; import os
    &gt;&gt;&gt; os.system(&#39;ls&#39;)
    file.txt README
    0

What is return value of [`os.system()`](https://docs.python.org/2/library/os.html#os.system)?  Why I get 0?

What is the return value of os.system() in Python?

I have to use [Python][1] and [Django][2] for our application. So I have two versions of Python, 2.6 and 2.7. Now I have installed Django. I could run the sample application for testing Django succesfuly. But how do I make sure whether Django uses the 2.6 or 2.7 version and what version of modules Django uses?

  [1]: http://en.wikipedia.org/wiki/Python_%28programming_language%29
  [2]: http://en.wikipedia.org/wiki/Django_%28web_framework%29


How to check Django version

I know that I can do:

    try:
        # do something that may fail
    except:
        # do this if ANYTHING goes wrong

I can also do this:

    try:
        # do something that may fail
    except IDontLikeYouException:
        # say please
    except YouAreTooShortException:
        # stand on a ladder

But if I want to do the same thing inside two different exceptions, the best I can think of right now is to do this:

    try:
        # do something that may fail
    except IDontLikeYouException:
        # say please
    except YouAreBeingMeanException:
        # say please

Is there any way that I can do something like this (since the action to take in both exceptions is to `say please`):

    try:
        # do something that may fail
    except IDontLikeYouException, YouAreBeingMeanException:
        # say please

Now this really won&#39;t work, as it matches the syntax for:

    try:
        # do something that may fail
    except Exception, e:
        # say please

So, my effort to catch the two distinct exceptions doesn&#39;t exactly come through.

Is there a way to do this?

Catch multiple exceptions in one line (except block)

How can Flask / SQLAlchemy be configured to create a new database connection if one is not present?

I have an infrequently visited Python / Flask server which uses SQLAlchemy. It gets visited every couple of days, and on the first visit it often throws a &quot;MySQL server has gone away&quot; error. Subsequent page views are fine, but it looks unprofessional to have this initial error.

I&#39;d like to know the correct way to handle this - advice like &quot;make a really long time out&quot;, which would be about 4 days long in this case, doesn&#39;t seem correct. How can I test for the lack of a database connection and create one if needed?

Avoiding &quot;MySQL server has gone away&quot; on infrequently used Python / Flask server with SQLAlchemy

I&#39;m setting up the Django admin to the following models:
                                          
```python                                    
class Tag(models.Model):                                                 
    name = models.CharField(max_length=100)                                 

class Quote(models.Model):                                                  
    author = models.CharField(max_length=100)                               
    quote = models.CharField(max_length=1000)                               
    tags = models.ManyToManyField(Tag)
```

With the following code:

    class TagInline(admin.TabularInline):                                                                                               
        model = Tag                                                             
                                                                                
    class QuoteAdmin(admin.ModelAdmin):                                         
        list_display = (&#39;author&#39;, &#39;quote&#39;)                                      
        inlines = (TagInline,)                                                  
                                                                                
    class TagAdmin(admin.ModelAdmin):                                           
        pass                                                                    
                                                                                
    admin.site.register(Quote, QuoteAdmin)                                      
    admin.site.register(Tag, TagAdmin)

When trying to view the admin page to add a `Quote`, the page shows an error saying `&lt;class &#39;quotes.models.Tag&#39;&gt; has no ForeignKey to &lt;class &#39;quotes.models.Quote&#39;&gt;`. This didn&#39;t happen before I added an inline. What&#39;s the problem? How do I correctly add a `Tag` as an inline?

*(I spent a good 20 minutes searching for an answer; I found similar questions but none of their answers worked for me.)*

Django admin ManyToMany inline &quot;has no ForeignKey to&quot; error

I have a query akin to the following:

```sql
SELECT SUM(ISNULL(table.name)) FROM table
```

How does that `SUM` translate into a `QuerySet` in Django? i.e. What operation `xyz` does it translate to, in something like `MyModel.objects.xyz()`?

Django SUM Query?

I am using Django to build a website with MySQL. Now as I am learning so I need to change the Model very often so I want that all tables get cleared and new table get created.

But `syncdb` doesn&#39;t touch existing tables. Is there any  better way to handle this problem?


What is the easiest way to clear a database from the CLI with manage.py in Django?

I have models in Django set up as below. 


    class Pupil(models.Model):
    	forename = models.CharField(max_length=30)
    	surname = models.CharField(max_length=30)
    	dateofbirth = models.DateField()
    	year = models.IntegerField()
    	class_group = models.CharField(max_length=30)
    	email = models.EmailField(blank=True)
    	assignments = models.ManyToManyField(&#39;Assignment&#39;, verbose_name=&#39;related assignments&#39;)
    
    	def __unicode__(self):
    		return u&#39;%s %s&#39; % (self.forename, self.surname)
    
    class Subject(models.Model):
    	name = models.CharField(max_length=30)
    	level = models.CharField(max_length=30)
    	teachers = models.ManyToManyField(&#39;Teacher&#39;, verbose_name=&#39;related teachers&#39;)
    
    	def __unicode__(self):
    		return self.name
    
    class Teacher(models.Model):
    	forename = models.CharField(max_length=30)
    	surname = models.CharField(max_length=30)
    	email = models.EmailField(blank=True)
    
    	def __unicode__(self):
    		return u&#39;%s %s&#39; % (self.forename, self.surname)
    
    class Assignment(models.Model):
    	assignment_name = models.CharField(max_length=30)
    	date_assigned = models.DateField()
    	date_submitted = models.DateField()
    
    	def __unicode__(self):
    		return self.assignment_name

When I attempt to add a pupil and attach an assignment to the pupil in the admin, I get a database error -  

    no such table: homework_pupil_assignments

after reading [this][1] I realised this could be due to django not updating changes to my models as when I do `manage.py sqlall homework`


I see the following:

    BEGIN;
    CREATE TABLE &quot;homework_pupil_assignments&quot; (
        &quot;id&quot; integer NOT NULL PRIMARY KEY,
        &quot;pupil_id&quot; integer NOT NULL,
        &quot;assignment_id&quot; integer NOT NULL,
        UNIQUE (&quot;pupil_id&quot;, &quot;assignment_id&quot;)
    )
    ;
    CREATE TABLE &quot;homework_pupil&quot; (
        &quot;id&quot; integer NOT NULL PRIMARY KEY,
        &quot;forename&quot; varchar(30) NOT NULL,
        &quot;surname&quot; varchar(30) NOT NULL,
        &quot;dateofbirth&quot; date NOT NULL,
        &quot;year&quot; integer NOT NULL,
        &quot;class_group&quot; varchar(30) NOT NULL,
        &quot;email&quot; varchar(75) NOT NULL
    )
    ;
    CREATE TABLE &quot;homework_subject_teachers&quot; (
        &quot;id&quot; integer NOT NULL PRIMARY KEY,
        &quot;subject_id&quot; integer NOT NULL,
        &quot;teacher_id&quot; integer NOT NULL,
        UNIQUE (&quot;subject_id&quot;, &quot;teacher_id&quot;)
    )
    ;
    CREATE TABLE &quot;homework_subject&quot; (
        &quot;id&quot; integer NOT NULL PRIMARY KEY,
        &quot;name&quot; varchar(30) NOT NULL,
        &quot;level&quot; varchar(30) NOT NULL
    )
    ;
    CREATE TABLE &quot;homework_teacher&quot; (
        &quot;id&quot; integer NOT NULL PRIMARY KEY,
        &quot;forename&quot; varchar(30) NOT NULL,
        &quot;surname&quot; varchar(30) NOT NULL,
        &quot;email&quot; varchar(75) NOT NULL
    )
    ;
    CREATE TABLE &quot;homework_assignment&quot; (
        &quot;id&quot; integer NOT NULL PRIMARY KEY,
        &quot;assignment_name&quot; varchar(30) NOT NULL,
        &quot;date_assigned&quot; date NOT NULL,
        &quot;date_submitted&quot; date NOT NULL
    )
    ;
    COMMIT;


I then installed South, following the directions to get up and running with an existing app, in the hope of successfully syncing these tables. No joy. 

Can anyone suggest how I can get the database (sqlite3) to reflect the models or point out what I&#39;m doing wrong?



  [1]: https://stackoverflow.com/questions/10077721/django-databaseerror-no-such-table

django no such table:

I am trying to apply a migration but am getting the error:

&gt; django.db.utils.OperationalError: (1050, &quot;Table &#39;customers_customer&#39;
&gt; already exists&quot;)

I get this by issuing the following command:

    python manage.py migrate

My customer table already exists, so what do I do to let the migration know this, not error out, and run my modification to my model?


I ran this on my local environment with local database with no problem.  It is when I pointed my database to production and ran `migrate` above that I get this error.

django 1.7 migrate gets error &quot;table already exists&quot;

(I know there is a title the same as this, but the question is different). 

I have managed to get my development machine migrations and production migrations out of sync. 

I have a Django app which was using South. I had my own workflow that worked fine (it probably wasn&#39;t the correct way to do things, but I had no problems with it). 

Basically I have a script that copies the production database dump to my development machine. It also copied the migration files. That way the two were in synch, and I could run South commands as normal. 


Now I have upgraded to 1.7, and started using migrations. When I use my previous workflow (copy database dump, and migration files from production), it is not detecting changes on my development machine.

I have read through the migrations document, and I see that the correct way to use it is to 

 1. run &quot;make migrations&quot; and &quot;migrate&quot; on my development machine.
 2. run &quot;migrate&quot; on my devlopemnt machine to actually make the database changes
 3. Copy changes over, including migration files.
 4. run &quot;migrate&quot; on the production machine. (without the &quot;makemigrations&quot; step)

Anyway. It is all a mess now. I would like to &quot;reset&quot; my migrations and start from scratch, doing things properly from now on.

What do I need to do? 

 1. Delete the contents of the migration table (on both machines)?
 2. Delete the contents of the migration folder? (Including the __init__.py file).  
 3. Start the migrations as per the documentation for a new one.

Have I missed anything?
Is there a reason why copying everything from production(database and migration files) doesn&#39;t detect any changes on my development machine afterwards

How to reset migrations in Django 1.7

According to the documentation here:
https://docs.djangoproject.com/en/1.8/topics/migrations/ it says:
    
    migrate, which is responsible for applying migrations, as well as unapplying and listing their status.

and

    makemigrations, which is responsible for creating new migrations based on the changes you have made to your models.

From what I understand, I first do

    makemigrations

to create the migration file and then do

    migrate

to actually apply the migration?

Do note though that I just began my Django project and I added my app to my &quot;installed_apps&quot; list. After that, I did

    python manage.py runserver

and it said 

    You have unapplied migrations; your app may not work properly until they are applied. Run &#39;python manage.py migrate&#39; to apply them.

It didn&#39;t mention anything about running makemigrations.


Content Type	Original Author	Original Content on Stackoverflow
Question	CJ Gaconnet	View Question on Stackoverflow
Solution 1 - Python	Chris Pratt	View Answer on Stackoverflow

Can you migrate backwards to before the first migration in South?

Python Problem Overview

Python Solutions

Solution 1 - Python

What is the difference between #define and const?

SQLite Schema Information Metadata

Attributions