cs-djutils 20250219

My collection of things for working with Django.

My collection of things for working with Django.

Latest release 20250219:

• model_batches_qs: accept a nonmapping for exclude= or filter= eg a Q() function.
• model_batches_qs: new optional only= parameter.

Presently this provides:

• BaseCommand: a drop in replacement for django.core.management.base.BaseCommand which uses a cs.cmdutils.BaseCommand style of implementation
• model_batches_qs: a generator yielding QuerySets for batches of a Model

Class BaseCommand(cs.cmdutils.BaseCommand, django.core.management.base.BaseCommand)

A drop in class for django.core.management.base.BaseCommand which subclasses cs.cmdutils.BaseCommand.

This lets me write management commands more easily, particularly if there are subcommands.

This is a drop in in the sense that you still make a management command in nearly the same way:

from cs.djutils import BaseCommand

class Command(BaseCommand):

and manage.py will find it and run it as normal. But from that point on the style is as for cs.cmdutils.BaseCommand:

• no argparse setup
• direct support for subcommands as methods
• succinct option parsing, if you want additional command line options
• usage text in the subcommand method docstring

A simple command looks like this:

class Command(BaseCommand):

    def main(self, argv):
        """ Usage: {cmd} .......
              Do the main thing.
        """
        ... do stuff based on the CLI args `argv` ...

A command with subcommands looks like this:

class Command(BaseCommand):

    def cmd_this(self, argv):
        """ Usage: {cmd} ......
              Do this.
        """
        ... do the "this" subcommand ...

    def cmd_that(self, argv):
        """ Usage: {cmd} ......
              Do that.
        """
        ... do the "that" subcommand ...

If want some kind of app/client specific "overcommand" composed from other management commands you can import them and make them subcommands of the overcommand:

from .other_command import Command as OtherCommand

class Command(BaseCommand):

    # provide it as the "other" subcommand
    cmd_other = OtherCommand

Option parsing is inline in the command. self comes presupplied with a .options attribute which is an instance of cs.cmdutils.BaseCommandOptions (or some subclass).

Parsing options is light weight and automatically updates the usage text. This example adds command line switches to the default switches:

• -x: a Boolean, setting self.options.x
• --thing-limit n: an int, setting self.options.thing_limit=n
• --mode blah: a string, setting self.options.mode=blah

Code sketch:

from cs.cmdutils import popopts

class Command(BaseCommand):

    @popopts(
        x=None,
        thing_limit_=int,
        mode_='The run mode.',
    )
    def cmd_this(self, argv):
        """ Usage: {cmd}
              Do this thing.
        """
        options = self.options
        ... now consult options.x or whatever
        ... argv is now the remaining arguments after the options

BaseCommand.Options

BaseCommand.SubCommandClass

BaseCommand.add_arguments(self, parser): Add the Options.COMMON_OPT_SPECS to the argparse parser. This is basicly to support the Django call_command function.

BaseCommand.handle(*, argv, **options): The Django BaseComand.handle method. This creates another instance for argv and runs it.

BaseCommand.run_from_argv(argv): Intercept django.core.management.base.BaseCommand.run_from_argv. Construct an instance of cs.djutils.DjangoBaseCommand and run it.

Class DjangoSpecificSubCommand(cs.cmdutils.SubCommand)

A subclass of cs.cmdutils.SubCOmmand with additional support for Django's BaseCommand.

DjangoSpecificSubCommand.__call__(self, argv: List[str]): Run this SubCommand with argv. This calls Django's BaseCommand.run_from_argv for pure Django commands.

DjangoSpecificSubCommand.is_pure_django_command: Whether this subcommand is a pure Django BaseCommand.

DjangoSpecificSubCommand.usage_text(self, *, cmd=None, **kw): Return the usage text for this subcommand.

model_batches_qs(model: django.db.models.base.Model, field_name='pk', *, chunk_size=1024, desc=False, exclude=None, filter=None, only=None) -> Iterable[django.db.models.query.QuerySet]

A generator yielding QuerySets which produce nonoverlapping batches of Model instances.

Efficient behaviour requires the field to be indexed. Correct behaviour requires the field values to be unique.

See model_instances for an iterable of instances wrapper of this function, where you have no need to further amend the QuerySets or to be aware of the batches.

Parameters:

• model: the Model to query
• field_name: default 'pk', the name of the field on which to order the batches
• chunk_size: the maximum size of each chunk
• desc: default False; if true then order the batches in descending order instead of ascending order
• exclude: optional mapping of Django query terms to exclude by
• filter: optional mapping of Django query terms to filter by
• only: optional sequence of field names for a Django query .only()

Example iteration of a Model would look like:

from itertools import chain
from cs.djutils import model_batches_qs
for instance in chain.from_iterable(model_batches_qs(MyModel)):
    ... work with instance ...

By returning QuerySets it is possible to further alter each query:

from cs.djutils import model_batches_qs
for batch_qs in model_batches_qs(MyModel):
    for result in batch_qs.filter(
        some_field__gt=10
    ).select_related(.......):
        ... work with each result in the batch ...

or:

from itertools import chain
from cs.djutils import model_batches_qs
for result in chain.from_iterable(
    batch_qs.filter(
        some_field__gt=10
    ).select_related(.......)
    for batch_qs in model_batches_qs(MyModel)
):
        ... work with each result ...

model_instances(model: django.db.models.base.Model, field_name='pk', only=None, **mbqs_kw) -> Iterable[django.db.models.base.Model]

A generator yielding Model instances. This is a wrapper for model_batches_qs and accepts the same arguments.

Efficient behaviour requires the field to be indexed. Correct behaviour requires the field values to be unique.

Release Log

Release 20250219:

• model_batches_qs: accept a nonmapping for exclude= or filter= eg a Q() function.
• model_batches_qs: new optional only= parameter.

Release 20250213: New model_instances() wrapper for model_batches_qs() returning an iterable of Model instances.

Release 20250113.2: model_batches_qs: bugfix second and following QuerySet construction.

Release 20250113.1: model_batches_qs: new exclude=dict and filter=dict optional parameters to filter before the slice.

Release 20250113: model_batches_qs: improve the query which measures the current batch.

Release 20250111.1: Documentation update.

Release 20250111: New model_batches_qs() generator yielding QuerySets for batches of a Model.

Release 20241222.3: Autocall settings.configure() if required because Django's settings object is a royal PITA.

Release 20241222.2: BaseCommand.Options.settings: call settings.configure() on init if that has not already been done.

Release 20241222.1: Placate the dataclass - upgrade BaseCommand.Options.settings to be a field() with a default_factory.

Release 20241222: BaseCommand.Options: include .settings with the public django.conf.settings names, mostly for cmd_info and cmd_repl.

Release 20241119: New DjangoSpecificSubCommand(CSBaseCommand.SubCommandClass) to include support for pure Django BaseCommands.

Release 20241111: Rename DjangoBaseCommand to just BaseCommand so that we go from cs.djutils import BaseCommand. Less confusing.

Release 20241110: Initial PyPI release with DjangoBaseCommand, cs.cmdutils.BaseCommand subclass suppplanting django.core.management.base.BaseCommand.