A large text field, stored compressed in the database, for Django and MySQL.
Project description
django-mysql-compressed-fields
This package provides CompressedTextField, a MySQL-specific Django model field similar to TextField or CharField that stores its value in compressed form via zlib.
In particular you can replace a TextField or CharField like:
from django.db import models
class ProjectTextFile(models.Model):
content = models.TextField(blank=True)
with:
from django.db import models
from mysql_compressed_fields import CompressedTextField
class ProjectTextFile(models.Model):
content = CompressedTextField(blank=True)
such that the text value of the field is actually compressed in the database.
String-based lookups are supported:
html_files = ProjectTextFile.objects.filter(content__contains='<html')
html_files = ProjectTextFile.objects.filter(content__startswith='<!DOCTYPE')
html_files = ProjectTextFile.objects.filter(content__endswith='</html>')
empty_html_files = ProjectTextFile.objects.filter(content__in=['', '<html></html>'])
Advanced manipulations with MySQL's COMPRESS(), UNCOMPRESS(), and UNCOMPRESSED_LENGTH() functions are also supported:
from django.db.models import F
from mysql_compressed_fields import UncompressedLength
files = ProjectTextFile.objects.only('id').annotate(
content_length=UncompressedLength(F('content'))
)
Dependencies
License
Migration Steps
To migrate an existing TextField or CharField to be a CompressedTextField:
- Install this package:
pip3 install django-mysql-compressed-fields
- Find an existing Django model with an uncompressed TextField or CharField that you want to compress. For example:
from django.db import models
class ProjectTextFile(models.Model):
content = models.TextField(blank=True)
- Add a
*_compressedsibling field that will be used to hold the compressed version of the original field. Mark it asdefault=''. Include an explicitdb_column=...value:
from django.db import models
from mysql_compressed_fields import CompressedTextField
class ProjectTextFile(models.Model):
content = models.TextField(blank=True)
content_compressed = CompressedTextField(
blank=True,
default='', # needed by Django when adding a field
db_column='content_compressed', # pin column name
)
- Generate a migration to add the compressed field:
python3 manage.py makemigrations
- Generate a new empty migration in the same app where the field is defined,
which we will use to populate the compressed field:
python3 manage.py makemigrations --empty __APP_NAME__
- Open the empty migration file. It should look something like:
from django.db import migrations
class Migration(migrations.Migration):
dependencies = [
('ide', '0002_projecttextfile_content_compressed'),
]
operations = [
]
- Edit the
operationsfield to use a RunPython step to populate the compressed field from the uncompressed field:
from django.db import migrations
from django.db.models import F
from mysql_compressed_fields import Compress
def _populate_content_compressed(apps, schema_editor):
ProjectTextFile = apps.get_model('ide', 'ProjectTextFile')
# NOTE: Assumes "content" field is already UTF-8 encoded,
# because CompressedTextField assumes UTF-8 encoding.
ProjectTextFile.objects.update(content_compressed=Compress(F('content')))
class Migration(migrations.Migration):
dependencies = [
('ide', '0002_projecttextfile_content_compressed'),
]
operations = [
migrations.RunPython(
code=_populate_content_compressed,
reverse_code=migrations.RunPython.noop,
atomic=False,
)
]
- Remove the original uncompressed field from the model, leaving only the compressed field remaining:
from django.db import models
from mysql_compressed_fields import CompressedTextField
class ProjectTextFile(models.Model):
content_compressed = CompressedTextField(
blank=True,
default='', # needed by Django when adding a field
db_column='content_compressed', # pin column name
)
- Generate a migration to remove the uncompressed field:
python3 manage.py makemigrations
- Rename the compressed field without the
*_compressedsuffix so that it now has the name of the original uncompressed field:
from django.db import models
from mysql_compressed_fields import CompressedTextField
class ProjectTextFile(models.Model):
content = CompressedTextField(
blank=True,
default='', # needed by Django when adding a field
db_column='content_compressed', # pin column name
)
- Generate a migration to rename the field:
python3 manage.py makemigrations- When prompted whether the field was renamed, answer
y(for yes).
- You now have a compressed version of the original field. All done! 🎉
Sponsor
This project is brought to you by TechSmart, which seeks to inspire the next generation of K-12 teachers and students to learn coding and create amazing things with computers. We use Django heavily.
API Reference
All classes and functions below should be imported directly from
mysql_compressed_fields. For example:
from mysql_compressed_fields import CompressedTextField
Fields
CompressedTextField
A large text field, stored compressed in the database.
Generally behaves like TextField. Stores values in the database using the same database column type as BinaryField. The value is compressed in the same format that MySQL's COMPRESS() function uses. Compression and decompression is performed by Django and not the database.
If you specify a max_length attribute, it will be reflected in the Textarea widget of the auto-generated form field. However it is not enforced at the model or database level. The max_length applies to the length of the uncompressed text rather than the compressed text.
String-based lookups can be used with this field type. Such lookups will transparently decompress the field on the database server.
html_files = ProjectTextFile.objects.filter(content__contains='<html')
html_files = ProjectTextFile.objects.filter(content__startswith='<!DOCTYPE')
html_files = ProjectTextFile.objects.filter(content__endswith='</html>')
empty_html_files = ProjectTextFile.objects.filter(content__in=['', '<html></html>'])
Note that F-expressions that reference this field type will always refer to the compressed value rather than the uncompressed value. So you may need to use the Compress() and Uncompress() database functions manually when working with F-expressions.
# Copy a TextField value (in utf8 collation) to a CompressedTextField
ProjectTextFile.objects.filter(...).update(content=Compress(F('name')))
# Copy a CompressedTextField value to a TextField (in utf8 collation)
ProjectTextFile.objects.filter(...).update(name=Uncompress(F('content')))
# Copy a CompressedTextField value to a CompressedTextField
ProjectTextFile.objects.filter(...).update(content=F('content'))
The default form widget for this field is a
django.contrib.admin.widgets.AdminTextareaWidget (a kind of TextInput).
Database functions
Compress
The MySQL COMPRESS() function, usable in F() expressions.
Uncompress
The MySQL UNCOMPRESS() function, usable in F() expressions.
UncompressedLength
The MySQL UNCOMPRESSED_LENGTH() function, usable in F() expressions.
compress
def compress(uncompressed_bytes: bytes) -> bytes:
The MySQL COMPRESS() function.
uncompress
def uncompress(compressed_bytes: bytes) -> bytes:
The MySQL UNCOMPRESS() function.
uncompressed_length
def uncompressed_length(compressed_bytes: bytes) -> int:
The MySQL UNCOMPRESSED_LENGTH() function.
compressed_length
def compressed_length(
uncompressed_bytes: bytes,
*, chunk_size: int=64 * 1000,
stop_if_greater_than: Optional[int]=None) -> int:
Returns the length of COMPRESS(uncompressed_bytes).
If stop_if_greater_than is specified and a result greater than
stop_if_greater_than is returned then the compressed length is
no less than the returned result.
Running Tests
- Install Docker.
- Install MySQL CLI tools:
- If macOS, install using brew:
brew install mysql-client@5.7 - Otherwise install from source: https://downloads.mysql.com/archives/community/
- If macOS, install using brew:
- Add MySQL CLI tools to path:
export PATH="/usr/local/opt/mysql-client@5.7/bin:$PATH"
- Start MySQL server:
docker run --name ide_db_server -e MYSQL_DATABASE=ide_db -e MYSQL_ROOT_PASSWORD=root -p 127.0.0.1:8889:3306 -d mysql:5.7
- Run tests:
cd tests/test_data/mysitepoetry installpoetry run python3 manage.py test
Release Notes
v1.1.0
- Fix to support Django 4.1
v1.0.1
- Add logo.
v1.0.0
- Initial release.
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