#36602: Enhance showmigrations command with structured data collection and
display
separation
-------------------------------------+-------------------------------------
Reporter: Aashay | Owner: Aashay Amballi
Amballi |
Type: | Status: assigned
Cleanup/optimization |
Component: Core | Version:
(Management commands) |
Severity: Normal | Keywords: showmigrations
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 1
UI/UX: 0 |
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Enhance the showmigrations command with structured data collection and
display separation
Add a get_migration_data() method to the showmigrations command that
returns migration data in a structured format, and modify show_list() to
accept this data as a parameter. This separation enables better
extensibility and customization while preserving all existing
functionality.
Problem
The current showmigrations command tightly couples data collection with
display logic, making it difficult to extend or customize the output
format. Third-party packages and custom commands cannot easily access
migration data in a structured format or customize the display without
duplicating Django's internal logic.
Why Not Just Create a Custom Command?
While it's possible to create a custom command for specific needs, many
use cases align closely with showmigrations functionality. Creating
separate commands leads to:
- Code Duplication: Replicating Django's migration loading and graph
traversal logic
- Maintenance Burden: Keeping custom commands in sync with Django's
internal changes
- Fragmentation: Multiple similar commands across the ecosystem
- Lost Benefits: Missing Django's built-in features (app filtering,
verbosity, etc.)
This enhancement would benefit the entire Django ecosystem by making
showmigrations more extensible while preserving its core functionality.
Request or proposal
proposal
Separate data collection from display logic by introducing a
get_migration_data() method that returns structured migration data, and
modify show_list() to accept this data as a parameter.
Benefits:
- Extensibility: Third-party packages can easily access migration data
- Testability: Data collection and display can be tested independently
- Maintainability: Cleaner separation of concerns
- Reusability: Migration data can be used by other methods
- Ecosystem Health: Reduces code duplication across Django packages
- Output Flexibility: Complete control over how the showmigration result
is displayed''
Proposed API:
{{{
class Command(BaseCommand):
def handle(self, *args, **options):
self.verbosity = options["verbosity"]
if options["format"] == "plan":
# We can apply a similar approach to the plan, also.
return self.show_plan(connection, options["app_label"])
else:
migration_data = self.get_migration_data(connection,
options["app_label"])
return self.show_list(migration_data)
def get_migration_data(self, connection, app_names=None):
"""
Return migration data in structured format.
Returns:
dict: {"app_name": [{"name": "0001_initial", "applied": True,
...}, ...]}
"""
# Current show_list logic moved here, but returns data instead of
printing
pass
def show_list(self, migration_data):
"""
Display migration data using provided data.
Args:
migration_data (dict): Migration data from
get_migration_data()
"""
# Display logic using migration_data parameter
pass
}}}
get_migration_data return data structure
{{{
{
"app_name": [
{"name": "0001_initial", "applied": True, ...},
{"name": "0002_add_field", "applied": False, ...},
# ...
],
# ...
}
}}}
Implementation Suggestions
Implementation Notes:
get_migration_data() should contain the current show_list() logic but
return data instead of printing
show_list() should be refactored to use the data parameter
Both methods should be easily overridable by subclasses
Example Usage:
{{{
# Custom command extending showmigrations
class CustomShowMigrationsCommand(ShowMigrationsCommand):
def get_migration_data(self, connection, app_names=None):
data = super().get_migration_data(connection, app_names)
# Add custom data (e.g., file sizes, creation dates, etc.), maybe
based on some custom flags
for app_name, migrations in data.items():
for migration in migrations:
migration_file = self.find_migration_file(app_name,
migration["name"])
if migration_file:
migration["file_size"] = migration_file.stat().st_size
migration["created_at"] =
migration_file.stat().st_ctime
return data
def show_list(self, migration_data):
# Custom display format with file sizes
for app_name, migrations in migration_data.items():
for migration in migrations:
status = "✓" if migration["applied"] else "✗"
file_size = migration.get("file_size", 0)
self.stdout.write(f" {status}
{app_name}.{migration['name']} ({file_size} bytes)")
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/36602>
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