crucial

I was getting an error while running unit tests and the test database was failing to be created.

django.db.utils.DatabaseError: relation "django_content_type" does not
exist

eventually found the problem.  I had the following in a file that was imported to a models.py:

hrd_type = ContentType.objects.get_for_model(HttpReferrerDomain)

The idea being that it can just set the var when it loads up and after that its always there.  But this means for creating a fresh database, the db is called to do this lookup right when the models.py is loaded.

There is one in django.core.exceptions and one in django.forms.util

Using that space age IDE Eclipse I have to say I’m enjoying how much time I’ve saved just going shift-command-O to organize and resolve all of my imports.  But today I’ve just lost a few hours due to my ok-ing the wrong class.

Quite mysterious it was, I raised a ValidationError (core exceptions one) in my form’s clean() and watched as the try: except ValidationError: in django’s full_clean() completely ignored my error and propagated it up.

But what is the django crüe doing naming two classes that ?  django.core.exceptions is quite vague, it just says “An error while validating data.”  Its used for db Field validation errors.  

I guess its as confusing as naming two entire class heirarchies 'Field’ : one for db fields and one for html form fields.  As though the two always went hand in hand, which they don’t.  

Another large problem I have recently is that a form field and its form widget are never allowed to talk to the object model, only to a single db field. I often have built fields that need to save to several fields on the model, and the clearest place to do this is by concentrating most of the power into the Form class.  

An example is an address input that I use that has a display address, postal address and map address.  The interface is complex, uses google maps and in the end also saves longitude,latitude, geo_accuracy, address, street, zip, city,state, and country objects. As a field or widget its not allowed to do all that.  It has to be tied to a form or the form has to call a function on the field to offer it access to the Model.

Another pet peeve (while we’ve got me in a tizzy still):

    # Give this new form class a reasonable name.

    if form ModelForm:

        class_name = model.name + 'Form’

    else:

        # CX: leave a clue that the form IS the form that you passed in

        # otherwise you have no clue what happened to your form class

        class_name = form.name + “FromFactory”

Compiling GDAL, I had a failure with the following splurge:

libtool: link: g++ -shared -nostdlib /usr/lib/gcc/x86_64-linux-gnu/4.4.1/../../../../lib/crti.o /usr/lib/gcc/x86_64-linux-gnu/4.4.1/crtbeginS.o .libs/libgdal.la.lnkscript  -L/usr/local/lib /usr/local/lib/libgeos_c.so /usr/local/lib/libgeos.so /usr/local/lib/libexpat.so -L/usr/lib -lpq -lrt -ldl /usr/lib/libcurl.so -lssl -lcrypto -lz -L/usr/lib/gcc/x86_64-linux-gnu/4.4.1 -L/usr/lib/gcc/x86_64-linux-gnu/4.4.1/../../../../lib -L/lib/../lib -L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/4.4.1/../../.. -lstdc++ -lm -lc -lgcc_s /usr/lib/gcc/x86_64-linux-gnu/4.4.1/crtendS.o /usr/lib/gcc/x86_64-linux-gnu/4.4.1/../../../../lib/crtn.o         -Wl,-soname -Wl,libgdal.so.1 -o .libs/libgdal.so.1.13.2

/usr/bin/ld: /usr/local/lib/libz.a(crc32.o): relocation R_X86_64_32 against `.rodata’ can not be used when making a shared object; recompile with -fPIC

/usr/local/lib/libz.a: could not read symbols: Bad value

collect2: ld returned 1 exit status

make¹: *** [libgdal.la] Error 1

make¹: Leaving directory `/home/crucial/tmp/gdal-1.6.2’

make: *** [check-lib] Error 2

MySQLdb is the python support bindings for MySQL.  Not that the name would lead you to beleive that.

Its sourceforge page calls it http://sourceforge.net/projects/mysql-python/ which makes more sense.

you need setuptools, which you usually already have:

    sudo aptitude install python-setuptools

You need MySQL-devel to compile, but its not called that, its called: libmysql++-dev on Ubuntu

    sudo apt-get install libmysql++-dev

download MySQLdb itself from:

    http://sourceforge.net/projects/mysql-python/

    # the version you download will be more recent

    tar xfz MySQL-python-1.2.3.tar.gz

    cd MySQL-python-1.2.3

    python setup.py build

    # the following might fail if it can’t find mysql_config on your path

    sudo python setup.py install

if it did try locating the mysql_config that was installed with MySQL-devel

and editing site.cfg which is in the MySQL-python folder

uncomment and point to it here: 

    mysql_config = /usr/bin/mysql_config

and try to build again

if it worked then test:

open a python shell (also change directories out of the compile dir you were just in to avoid confusing yourself with the just compiled version sitting in your path)

    import MySQLdb

When installing postgres a user will be created named 'postgres’ with a password of '!!’ which means “cannot login”.  But yet you need to login as that in order to run psql (the postgres db shell) to create other users and to create database templates.

The solution is to first log yourself in as root (in your normal shell):

su root

(enter password…)

then you will no longer be subject to password checks and you can login in as user 'postgres’

su postgres

(you will automatically allowed to do this)

then you can

psql

note: on OS X you cannot login as root.  use a binary install.  the King Khaos package was fairly painless for me.