add support to m2m

change cli options
add init-db cmd

aerich/ddl/__init__.py

@@ -1,6 +1,6 @@
 from typing import List, Type
 
-from tortoise import BaseDBAsyncClient, ForeignKeyFieldInstance, Model
+from tortoise import BaseDBAsyncClient, ForeignKeyFieldInstance, ManyToManyFieldInstance, Model
 from tortoise.backends.base.schema_generator import BaseSchemaGenerator
 from tortoise.fields import Field
 
@@ -8,7 +8,7 @@ from tortoise.fields import Field
 class BaseDDL:
     schema_generator_cls: Type[BaseSchemaGenerator] = BaseSchemaGenerator
     DIALECT = "sql"
-    _DROP_TABLE_TEMPLATE = "DROP TABLE {table_name} IF EXISTS"
+    _DROP_TABLE_TEMPLATE = "DROP TABLE IF EXISTS {table_name}"
     _ADD_COLUMN_TEMPLATE = "ALTER TABLE {table_name} ADD {column}"
     _DROP_COLUMN_TEMPLATE = "ALTER TABLE {table_name} DROP COLUMN {column_name}"
     _ADD_INDEX_TEMPLATE = (
@@ -17,6 +17,7 @@ class BaseDDL:
     _DROP_INDEX_TEMPLATE = "ALTER TABLE {table_name} DROP INDEX {index_name}"
     _ADD_FK_TEMPLATE = "ALTER TABLE {table_name} ADD CONSTRAINT `{fk_name}` FOREIGN KEY (`{db_column}`) REFERENCES `{table}` (`{field}`) ON DELETE {on_delete}"
     _DROP_FK_TEMPLATE = "ALTER TABLE {table_name} DROP FOREIGN KEY {fk_name}"
+    _M2M_TABLE_TEMPLATE = "CREATE TABLE {table_name} ({backward_key} {backward_type} NOT NULL REFERENCES {backward_table} ({backward_field}) ON DELETE CASCADE,{forward_key} {forward_type} NOT NULL REFERENCES {forward_table} ({forward_field}) ON DELETE CASCADE){extra}{comment};"
 
     def __init__(self, client: "BaseDBAsyncClient"):
         self.client = client
@@ -25,6 +26,12 @@ class BaseDDL:
     def create_table(self, model: "Type[Model]"):
         raise NotImplementedError
 
+    def create_m2m_table(self, model: "Type[Model]", field: ManyToManyFieldInstance):
+        raise NotImplementedError
+
+    def drop_m2m(self, field: ManyToManyFieldInstance):
+        raise NotImplementedError
+
     def drop_table(self, model: "Type[Model]"):
         raise NotImplementedError
 

aerich/ddl/mysql/__init__.py

@@ -1,6 +1,6 @@
 from typing import List, Type
 
-from tortoise import ForeignKeyFieldInstance, Model
+from tortoise import ForeignKeyFieldInstance, ManyToManyFieldInstance, Model
 from tortoise.backends.mysql.schema_generator import MySQLSchemaGenerator
 from tortoise.fields import Field, JSONField, TextField, UUIDField
 
@@ -17,6 +17,28 @@ class MysqlDDL(BaseDDL):
     def drop_table(self, model: "Type[Model]"):
         return self._DROP_TABLE_TEMPLATE.format(table_name=model._meta.db_table)
 
+    def create_m2m_table(self, model: "Type[Model]", field: ManyToManyFieldInstance):
+        return self._M2M_TABLE_TEMPLATE.format(
+            table_name=field.through,
+            backward_table=model._meta.db_table,
+            forward_table=field.related_model._meta.db_table,
+            backward_field=model._meta.db_pk_column,
+            forward_field=field.related_model._meta.db_pk_column,
+            backward_key=field.backward_key,
+            backward_type=model._meta.pk.get_for_dialect(self.DIALECT, "SQL_TYPE"),
+            forward_key=field.forward_key,
+            forward_type=field.related_model._meta.pk.get_for_dialect(self.DIALECT, "SQL_TYPE"),
+            extra=self.schema_generator._table_generate_extra(table=field.through),
+            comment=self.schema_generator._table_comment_generator(
+                table=field.through, comment=field.description
+            )
+            if field.description
+            else "",
+        )
+
+    def drop_m2m(self, field: ManyToManyFieldInstance):
+        return self._DROP_TABLE_TEMPLATE.format(table_name=field.through)
+
     def add_column(self, model: "Type[Model]", field_object: Field):
         db_table = model._meta.db_table
         default = field_object.default