feincms3-data¶
Why¶
Utilities for loading and dumping database data as JSON.
These utilities (partially) replace Django’s built-in dumpdata
and
loaddata
management commands.
Suppose you want to move data between systems incrementally. In this case it
isn’t sufficient to only know the data which has been created or updated; you
also want to know which data has been deleted in the meantime. Django’s
dumpdata
and loaddata
management commands only support the former case,
not the latter. They also do not including dependent objects in the dump.
This package offers utilities and management commands to address these shortcomings.
How¶
pip install feincms3-data
.
Add feincms3_data
to INSTALLED_APPS
so that the included management
commands are discovered.
Add datasets somewhere describing the models and relationships you want to
dump, e.g. in a module named app.f3datasets
:
from feincms3_data.data import (
specs_for_app_models,
specs_for_derived_models,
specs_for_models,
)
from app.dashboard import models as dashboard_models
from app.world import models as world_models
def districts(args):
pks = [int(arg) for arg in args.split(",") if arg]
return [
*specs_for_models(
[world_models.District],
{
"filter": {"pk__in": pks},
"delete_missing": True,
},
),
*specs_for_models(
[world_models.Exercise],
{
"filter": {"district__in": pks},
"delete_missing": True,
},
),
# All derived non-abstract models which aren't proxies:
*specs_for_derived_models(
world_models.ExercisePlugin,
{
"filter": {"parent__district__in": pks},
"delete_missing": True,
},
),
]
def datasets():
return {
"articles": {
"specs": lambda args: specs_for_app_models(
"articles",
{"delete_missing": True},
),
},
"pages": {
"specs": lambda args: specs_for_app_models(
"pages",
{"delete_missing": True},
),
},
"teachingmaterials": {
"specs": lambda args: specs_for_models(
[
dashboard_models.TeachingMaterialGroup,
dashboard_models.TeachingMaterial,
],
{"delete_missing": True},
),
},
"districts": {
"specs": districts,
},
}
Add a setting with the Python module path to the specs function:
FEINCMS3_DATA_DATASETS = "app.f3datasets.datasets"
Now, to dump e.g. pages you would run:
./manage.py f3dumpdata pages > tmp/pages.json
To dump the districts with the primary key of 42 and 43 you would run:
./manage.py f3dumpdata districts:42,43 > tmp/districts.json
The resulting JSON file has three top-level keys:
"version": 1
: The version of the dump, because not versioning dumps is a recipe for pain down the road."specs": [...]
: A list of model specs."objects": [...]
: A list of model instances; uses the same serializer as Django’sdumpdata
, everything looks the same.
Model specs consist of the following fields:
"model"
: The lowercased label (app_label.model_name
) of a model."filter"
: A dictionary which can be passed to the.filter()
queryset method as keyword arguments; used for determining the objects to dump and the objects to remove after loading."delete_missing"
: This flag makes the loader delete all objects matching"filter"
which do not exist in the dump."ignore_missing_m2m"
: A list of field names where deletions of related models should be ignored when restoring. This may be especially useful when only transferring content partially between databases."save_as_new"
: If present and truish, objects are inserted using new primary keys into the database instead of (potentially) overwriting pre-existing objects."defer_values"
: A list of fields which should receive random garbage when loading initially and only receive their real value later. This is especially useful to avoid unique constraint errors when loading partial graphs.
The dumps can be loaded back into the database by running:
./manage.py f3loaddata -v2 tmp/pages.json tmp/districts.json
Each dump is processed in an individual transaction. The data is first loaded
into the database; at the end, data matching the filters but whose primary
key wasn’t contained in the dump is deleted from the database (if
"delete_missing": True
).
Change log¶
Fixed the broken argument validation of
./manage.py f3dumpdata
.Switched to hatchling and ruff.
Made
specs_for_*_models
helpers return a list instead of a generator.Changed the
assert
statement for checking the dump version into araise
statement since assertions could be optimized out.Renamed
InvalidSpec
toInvalidSpecError
to make ruff happier.Added an
objects
argument todump_specs
which allows overriding the list of objects to dump.
Added argument validation to
./manage.py f3dumpdata
instead of crashing when the dataset isn’t known.Added the
defer_values
spec field which allows specifying a list of fields whose real values should be deferred and only saved after missing data has been deleted. This is especially useful when you have unique fields where partial updates could produce constraint validation errors (unique constraints cannot be deferred it seems).
Added various tests for expected behavior.
Refactored
load_dump
to pass the code complexity checker.Added an expected failure test which shows that handling unique fields isn’t yet working in all cases.
Added Django 4.2a1 to the CI matrix.
Allowed data loading with
save_as_new
to work in more scenarios where the data contains cyclic dependencies.
Fixed a crash when using nullable foreign keys to a model which uses
save_as_new
.Fix a behavior when using
save_as_new
together withdelete_missing
: When the parent of a model with both flags set is updated, the content is now duplicated (because the old object hadn’t been removed and the new one has been saved according tosave_as_new
). Previously, the old object has been removed automatically. Worse, this made is impossible to usesave_as_new
for duplicating top-level objects (their object graph would be removed after inserting the copy). This change may still be backwards incompatible for you though, so better check twice.Fixed deletion of missing objects in the presence of protected objects by processing specs in reverse.
Changed
specs_for_derived_models
to skip proxy models instead of skipping unmanaged models.Started deferring constraints and resetting sequences when loading dumps.
Added Django 4.1.
Added the
mappers
argument todump_specs
which allows changing the serialized representation of models before writing the JSON.Changed
load_dump
to also validate specs.Replaced
FEINCMS3_DATA_SPECS
with the more flexible and opinionatedFEINCMS3_DATA_DATASETS
.
Initial release!