support multiple db transitions by keeping the backup-table dynamic

freqtrade/persistence.py

@@ -77,6 +77,13 @@ def check_migrate(engine) -> None:
     inspector = inspect(engine)
 
     cols = inspector.get_columns('trades')
+    tabs = inspector.get_table_names()
+    table_back_name = 'trades_bak'
+    i = 0
+    while table_back_name in tabs:
+        i += 1
+        table_back_name = f'trades_bak{i}'
+        logger.info(f'trying {table_back_name}')
 
     # Check for latest column
     if not has_column(cols, 'max_rate'):
@@ -87,7 +94,7 @@ def check_migrate(engine) -> None:
         max_rate = get_column_def(cols, 'max_rate', '0.0')
 
         # Schema migration necessary
-        engine.execute("alter table trades rename to trades_bak")
+        engine.execute(f"alter table trades rename to {table_back_name}")
         # let SQLAlchemy create the schema as required
         _DECL_BASE.metadata.create_all(engine)
 
@@ -112,8 +119,7 @@ def check_migrate(engine) -> None:
                 stake_amount, amount, open_date, close_date, open_order_id,
                 {stop_loss} stop_loss, {initial_stop_loss} initial_stop_loss,
                 {max_rate} max_rate
-
+                from {table_back_name}
-                from trades_bak
              """)
 
         # Reread columns - the above recreated the table!

freqtrade/tests/test_persistence.py

@@ -7,6 +7,7 @@ from sqlalchemy import create_engine
 
 from freqtrade import constants, OperationalException
 from freqtrade.persistence import Trade, init, clean_dry_run_db
+from freqtrade.tests.conftest import log_has
 
 
 @pytest.fixture(scope='function')
@@ -405,7 +406,7 @@ def test_migrate_old(mocker, default_conf, fee):
     assert trade.initial_stop_loss == 0.0
 
 
-def test_migrate_new(mocker, default_conf, fee):
+def test_migrate_new(mocker, default_conf, fee, caplog):
     """
     Test Database migration (starting with new pairformat)
     """
@@ -442,6 +443,9 @@ def test_migrate_new(mocker, default_conf, fee):
     # Create table using the old format
     engine.execute(create_table_old)
     engine.execute(insert_table_old)
+
+    # fake previous backup
+    engine.execute("create table trades_bak as select * from trades")
     # Run init to test migration
     init(default_conf)
 
@@ -456,6 +460,10 @@ def test_migrate_new(mocker, default_conf, fee):
     assert trade.stake_amount == default_conf.get("stake_amount")
     assert trade.pair == "ETC/BTC"
     assert trade.exchange == "binance"
+    assert trade.max_rate == 0.0
+    assert trade.stop_loss == 0.0
+    assert trade.initial_stop_loss == 0.0
+    assert log_has("trying trades_bak1", caplog.record_tuples)
 
 
 def test_adjust_stop_loss(limit_buy_order, limit_sell_order, fee):