diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 4ef48eb..4e9ae04 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -6,7 +6,8 @@ ChangeLog
 ===
 0.1.5
 -----
-- Add sqlite and postgres support
+- Add sqlite and postgres support.
+- Fix dependency import.
 
 0.1.4
 -----
diff --git a/aerich/migrate.py b/aerich/migrate.py
index 3cdb299..32ef420 100644
--- a/aerich/migrate.py
+++ b/aerich/migrate.py
@@ -13,15 +13,9 @@ from tortoise import (
     Model,
     Tortoise,
 )
-from tortoise.backends.asyncpg.schema_generator import AsyncpgSchemaGenerator
-from tortoise.backends.mysql.schema_generator import MySQLSchemaGenerator
-from tortoise.backends.sqlite.schema_generator import SqliteSchemaGenerator
 from tortoise.fields import Field
 
 from aerich.ddl import BaseDDL
-from aerich.ddl.mysql import MysqlDDL
-from aerich.ddl.postgres import PostgresDDL
-from aerich.ddl.sqlite import SqliteDDL
 from aerich.exceptions import ConfigurationError
 from aerich.utils import get_app_connection
 
@@ -78,11 +72,17 @@ class Migrate:
         await Tortoise.init(config=migrate_config)
 
         connection = get_app_connection(config, app)
-        if connection.schema_generator is MySQLSchemaGenerator:
+        if connection.schema_generator.DIALECT == "mysql":
+            from aerich.ddl.mysql import MysqlDDL
+
             cls.ddl = MysqlDDL(connection)
-        elif connection.schema_generator is SqliteSchemaGenerator:
+        elif connection.schema_generator.DIALECT == "sqlite":
+            from aerich.ddl.sqlite import SqliteDDL
+
             cls.ddl = SqliteDDL(connection)
-        elif connection.schema_generator is AsyncpgSchemaGenerator:
+        elif connection.schema_generator.DIALECT == "postgres":
+            from aerich.ddl.postgres import PostgresDDL
+
             cls.ddl = PostgresDDL(connection)
         else:
             raise NotImplementedError("Current only support MySQL")
diff --git a/tests/models.py b/tests/models.py
index ea0311c..c6f5073 100644
--- a/tests/models.py
+++ b/tests/models.py
@@ -30,9 +30,6 @@ class User(Model):
     avatar = fields.CharField(max_length=200, default="")
     intro = fields.TextField(default="")
 
-    def __str__(self):
-        return f"{self.pk}#{self.username}"
-
 
 class Category(Model):
     slug = fields.CharField(max_length=200)
@@ -40,9 +37,6 @@ class Category(Model):
     user = fields.ForeignKeyField("models.User", description="User")
     created_at = fields.DatetimeField(auto_now_add=True)
 
-    def __str__(self):
-        return f"{self.pk}#{self.name}"
-
 
 class Product(Model):
     categories = fields.ManyToManyField("models.Category")
@@ -55,15 +49,9 @@ class Product(Model):
     body = fields.TextField()
     created_at = fields.DatetimeField(auto_now_add=True)
 
-    def __str__(self):
-        return f"{self.pk}#{self.name}"
-
 
 class Config(Model):
     label = fields.CharField(max_length=200)
     key = fields.CharField(max_length=20)
     value = fields.JSONField()
     status: Status = fields.IntEnumField(Status, default=Status.on)
-
-    def __str__(self):
-        return f"{self.pk}#{self.label}"
diff --git a/tests/test_ddl.py b/tests/test_ddl.py
index 224a7f7..0ed2897 100644
--- a/tests/test_ddl.py
+++ b/tests/test_ddl.py
@@ -48,7 +48,6 @@ class TestDDL(test.TruncationTestCase):
 );""",
             )
         elif isinstance(self.ddl, PostgresDDL):
-            print(ret)
             self.assertEqual(
                 ret,
                 """CREATE TABLE IF NOT EXISTS "category" (
diff --git a/tests/test_migrate.py b/tests/test_migrate.py
deleted file mode 100644
index bd82e01..0000000
--- a/tests/test_migrate.py
+++ /dev/null
@@ -1,5 +0,0 @@
-from tortoise.contrib import test
-
-
-class TestMigrate(test.TruncationTestCase):
-    pass