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django-migration-linter/docs/incompatibilities.md
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# Backward incompatible migrations
The linter analyses your migrations and checks the SQL for:
- Added `NOT NULL` columns, which don't have a DEFAULT value
- Dropping columns
- Dropping tables
- Renaming columns
- Renaming tables
- Altering columns (which can be backward compatible and potentially ignored)
- Adding a unique constraint
Those are the most important and frequent backward incompatible migrations.
We are happy to add more if you can specify them to us.
## Warnings
On data migrations, the linter will show a warning when:
* you are missing a reverse migration
* the RunPython arguments do not respect the naming convention `apps, schema_editor`
* the model variable name is different from the model class name in the `get_model` call
## Codes
You can ignore check through the `--exclude-migration-test` option and specifying any of the codes:
| Code | Description |
|-----------------------------------|----------------------------------------------------------------------|
|`NOT_NULL` | Not NULL constraint on columns
|`DROP_COLUMN` | Dropping columns
|`DROP_TABLE` | Dropping tables
|`RENAME_COLUMN` | Renaming columns
|`RENAME_TABLE` | Renaming tables
|`ALTER_COLUMN` | Altering columns (could be backward compatible)
|`ADD_UNIQUE` | Add unique constraints
|`RUNPYTHON_REVERSIBLE` | RunPython data migration is not reversible (missing reverse code)
|`RUNPYTHON_ARGS_NAMING_CONVENTION` | By convention, RunPython names two arguments: apps, schema_editor
|`RUNPYTHON_MODEL_IMPORT` | Missing apps.get_model() calls for model
|`RUNPYTHON_MODEL_VARIABLE_NAME` | The model variable name is different from the model class itself
|`RUNSQL_REVERSIBLE` | RunSQL data migration is not reversible (missing reverse SQL)
|`CREATE_INDEX` | (Postgresql specific) Creating an index without the concurrent keyword will lock the table and may generate downtime
|`DROP_INDEX` | (Postgresql specific) Dropping an index without the concurrent keyword will lock the table and may generate downtime
|`REINDEX` | (Postgresql specific) Reindexing will lock the table and may generate downtime