PsqlDos: Make hash reset migrations more explicit

The `django_0039_reset_hash.py` and `e797afa09270_reset_hash.py`
migrations reset the hash for all nodes by deleting the extra in which
it is stored. The migrations use the `drop_hashes` function from the
`aiida/storage/psql_dos/migrations/utils/integrity.py` module. At the
time, and currently, the key used to store the hash in the extras is
`_aiida_hash`. This key is hard-coded in the `integrity.py` module but
it should really be part of the migrations themselves if the function is
to be reused. If in the future the key is changed, the migration should
specify which key should be used.

aiida/storage/psql_dos/migrations/utils/integrity.py

@@ -186,14 +186,12 @@ def write_database_integrity_violation(results, headers, reason_message, action_
         handle.write(tabulate(results, headers))
 
 
-# Currently valid hash key
-_HASH_EXTRA_KEY = '_aiida_hash'
-
-
-def drop_hashes(conn):
+def drop_hashes(conn, hash_extra_key):
     """Drop hashes of nodes.
 
     Print warning only if the DB actually contains nodes.
+
+    :param hash_extra_key: The key in the extras used to store the hash at the time of this migration.
     """
     # Remove when https://github.com/PyCQA/pylint/issues/1931 is fixed
     # pylint: disable=no-name-in-module,import-error
@@ -204,5 +202,5 @@ def drop_hashes(conn):
     if n_nodes > 0:
         echo.echo_warning('Invalidating the hashes of all nodes. Please run "verdi rehash".', bold=True)
 
-    statement = text(f"UPDATE db_dbnode SET extras = extras #- '{{{_HASH_EXTRA_KEY}}}'::text[];")
+    statement = text(f"UPDATE db_dbnode SET extras = extras #- '{{{hash_extra_key}}}'::text[];")
     conn.execute(statement)

aiida/storage/psql_dos/migrations/versions/django_0039_reset_hash.py

@@ -28,9 +28,9 @@
 
 def upgrade():
     """Migrations for the upgrade."""
-    drop_hashes(op.get_bind())  # pylint: disable=no-member
+    drop_hashes(op.get_bind(), hash_extra_key='_aiida_hash')  # pylint: disable=no-member
 
 
 def downgrade():
     """Migrations for the downgrade."""
-    drop_hashes(op.get_bind())  # pylint: disable=no-member
+    drop_hashes(op.get_bind(), hash_extra_key='_aiida_hash')  # pylint: disable=no-member

aiida/storage/psql_dos/migrations/versions/e797afa09270_reset_hash.py

@@ -30,9 +30,9 @@
 
 def upgrade():
     """drop the hashes when upgrading"""
-    drop_hashes(op.get_bind())  # pylint: disable=no-member
+    drop_hashes(op.get_bind(), hash_extra_key='_aiida_hash')  # pylint: disable=no-member
 
 
 def downgrade():
     """drop the hashes also when downgrading"""
-    drop_hashes(op.get_bind())  # pylint: disable=no-member
+    drop_hashes(op.get_bind(), hash_extra_key='_aiida_hash')  # pylint: disable=no-member