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58ea7a360d
print_archives.library_file_id -> library_files.folder_id -> library_folders.archive_id -> print_archives. Three nullable SET NULL links, each reasonable alone, that together made a loop metadata.sorted_tables could not sort: it dropped those edges, warned on every backup and every restore, and could return an order placing a child before its parent -- which once imported library_files ahead of library_folders and killed a restore on a ForeignKeyViolation. The restore no longer depends on that order (it strips every foreign key before importing and adds them back after), but the backup export sorts the same way, and the warning ends with "may raise an error in a future release" -- which would break backup and restore on one upgrade. Marking one edge use_alter removes it from the sort graph, not from the database: PostgreSQL emits it as ALTER TABLE ADD CONSTRAINT, as it already did for every constraint on these three tables, and SQLite inlines it into CREATE TABLE, so ON DELETE SET NULL holds on both. Verified against PostgreSQL 16 and SQLite.
87 lines
3.5 KiB
Python
87 lines
3.5 KiB
Python
"""The schema has to be sortable, because backup and restore sort it.
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`metadata.sorted_tables` is asked for the order in three places: the backup
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export, the restore's import loop, and the loop that puts foreign keys back
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afterwards. Three nullable SET NULL links used to close a loop --
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print_archives.library_file_id -> library_files.folder_id ->
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library_folders.archive_id -> print_archives -- and SQLAlchemy answered a
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sort it could not make, with a warning on every backup and every restore:
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Cannot correctly sort tables; there are unresolvable cycles between
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tables "library_files, library_folders, print_archives" ... this warning
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may raise an error in a future release.
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Two things were wrong with living on that. The order it returns can place a
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child before its parent, which is what once imported library_files ahead of
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library_folders and killed a restore on a ForeignKeyViolation. And the
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sentence at the end is a promise: if it ever becomes an error, backup and
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restore break on the same upgrade.
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One edge of the loop is marked use_alter, which takes it out of the sort
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graph without taking the constraint out of the database.
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"""
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from __future__ import annotations
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import importlib
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import pkgutil
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import warnings
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from sqlalchemy import create_engine, inspect
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from backend.app.core.database import Base
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def _all_models_imported() -> None:
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"""Base.metadata is filled by imports, so a partial import means a partial
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schema -- and a cycle in a table nobody imported would not be found here."""
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import backend.app.models as models
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for module in pkgutil.iter_modules(models.__path__):
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importlib.import_module(f"backend.app.models.{module.name}")
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def test_the_schema_sorts_without_a_cycle_warning():
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_all_models_imported()
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with warnings.catch_warnings(record=True) as caught:
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warnings.simplefilter("always")
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assert Base.metadata.sorted_tables
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cycles = [str(w.message) for w in caught if "cycles" in str(w.message)]
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assert not cycles, (
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f"a new foreign key has closed a loop in the schema; backup and restore sort these tables: {cycles}"
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)
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def test_the_tables_that_used_to_cycle_sort_parents_first():
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"""The property the warning took away. Order is what the restore's import
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loop follows, and a child ahead of its parent is a FK violation."""
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_all_models_imported()
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order = [t.name for t in Base.metadata.sorted_tables]
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assert order.index("library_folders") < order.index("library_files"), (
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"library_files.folder_id points at library_folders"
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)
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assert order.index("library_files") < order.index("print_archives"), (
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"print_archives.library_file_id points at library_files"
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)
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def test_the_altered_constraint_still_exists_on_sqlite():
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"""use_alter asks for ALTER TABLE ADD CONSTRAINT, and SQLite has no such
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statement. It inlines the key into CREATE TABLE instead -- but if that ever
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stopped being true, deleting an archive would leave a dangling
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library_folders.archive_id rather than nulling it, silently."""
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_all_models_imported()
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engine = create_engine("sqlite://")
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Base.metadata.create_all(engine)
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keys = inspect(engine).get_foreign_keys("library_folders")
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archive_link = [k for k in keys if k["referred_table"] == "print_archives"]
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assert archive_link, f"library_folders lost its archive key: {keys}"
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assert archive_link[0]["constrained_columns"] == ["archive_id"]
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assert archive_link[0]["options"].get("ondelete") == "SET NULL"
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