diff --git a/docs/source/accounting.rst b/docs/source/accounting.rst
index 86acafd..a28cd51 100644
--- a/docs/source/accounting.rst
+++ b/docs/source/accounting.rst
@@ -15,14 +15,6 @@ Subpackages
 Submodules
 ----------
 
-accounting.database module
---------------------------
-
-.. automodule:: accounting.database
-   :members:
-   :undoc-members:
-   :show-inheritance:
-
 accounting.locale module
 ------------------------
 
diff --git a/src/accounting/__init__.py b/src/accounting/__init__.py
index 41dfbcb..7519d91 100644
--- a/src/accounting/__init__.py
+++ b/src/accounting/__init__.py
@@ -21,9 +21,12 @@ import typing as t
 from pathlib import Path
 
 from flask import Flask, Blueprint
+from flask_sqlalchemy import SQLAlchemy
 
 from accounting.utils.user import AbstractUserUtils
 
+db: SQLAlchemy = SQLAlchemy()
+"""The database instance."""
 data_dir: Path = Path(__file__).parent / "data"
 """The data directory."""
 
@@ -45,8 +48,8 @@ def init_app(app: Flask, user_utils: AbstractUserUtils,
     """
     # The database instance must be set before loading everything
     # in the application.
-    from .database import set_db
-    set_db(app.extensions["sqlalchemy"])
+    global db
+    db = app.extensions["sqlalchemy"]
     from .utils.user import init_user_utils
     init_user_utils(user_utils)
 
diff --git a/src/accounting/account/commands.py b/src/accounting/account/commands.py
index ea4785d..1634b8d 100644
--- a/src/accounting/account/commands.py
+++ b/src/accounting/account/commands.py
@@ -24,7 +24,7 @@ from secrets import randbelow
 import click
 from flask.cli import with_appcontext
 
-from accounting.database import db
+from accounting import db
 from accounting.models import BaseAccount, Account, AccountL10n
 from accounting.utils.user import has_user, get_user_pk
 
diff --git a/src/accounting/account/forms.py b/src/accounting/account/forms.py
index 52accbd..752c7d8 100644
--- a/src/accounting/account/forms.py
+++ b/src/accounting/account/forms.py
@@ -23,7 +23,7 @@ from flask_wtf import FlaskForm
 from wtforms import StringField, BooleanField
 from wtforms.validators import DataRequired, ValidationError
 
-from accounting.database import db
+from accounting import db
 from accounting.locale import lazy_gettext
 from accounting.models import BaseAccount, Account
 from accounting.utils.random_id import new_id
diff --git a/src/accounting/account/views.py b/src/accounting/account/views.py
index d284264..84029f4 100644
--- a/src/accounting/account/views.py
+++ b/src/accounting/account/views.py
@@ -23,7 +23,7 @@ from flask import Blueprint, render_template, session, redirect, flash, \
     url_for, request
 from werkzeug.datastructures import ImmutableMultiDict
 
-from accounting.database import db
+from accounting import db
 from accounting.locale import lazy_gettext
 from accounting.models import Account, BaseAccount
 from accounting.utils.next_url import inherit_next, or_next
diff --git a/src/accounting/base_account/commands.py b/src/accounting/base_account/commands.py
index 9699cd8..1621108 100644
--- a/src/accounting/base_account/commands.py
+++ b/src/accounting/base_account/commands.py
@@ -23,7 +23,7 @@ import click
 from flask.cli import with_appcontext
 
 from accounting import data_dir
-from accounting.database import db
+from accounting import db
 from accounting.models import BaseAccount, BaseAccountL10n
 
 
diff --git a/src/accounting/base_account/converters.py b/src/accounting/base_account/converters.py
index 10fe5b2..7180ac7 100644
--- a/src/accounting/base_account/converters.py
+++ b/src/accounting/base_account/converters.py
@@ -20,7 +20,7 @@
 from flask import abort
 from werkzeug.routing import BaseConverter
 
-from accounting.database import db
+from accounting import db
 from accounting.models import BaseAccount
 
 
diff --git a/src/accounting/currency/commands.py b/src/accounting/currency/commands.py
index 6a151fb..5c640cf 100644
--- a/src/accounting/currency/commands.py
+++ b/src/accounting/currency/commands.py
@@ -24,8 +24,7 @@ import typing as t
 import click
 from flask.cli import with_appcontext
 
-from accounting import data_dir
-from accounting.database import db
+from accounting import db, data_dir
 from accounting.models import Currency, CurrencyL10n
 from accounting.utils.user import has_user, get_user_pk
 
diff --git a/src/accounting/currency/converters.py b/src/accounting/currency/converters.py
index d696b65..55c6a70 100644
--- a/src/accounting/currency/converters.py
+++ b/src/accounting/currency/converters.py
@@ -20,7 +20,7 @@
 from flask import abort
 from werkzeug.routing import BaseConverter
 
-from accounting.database import db
+from accounting import db
 from accounting.models import Currency
 
 
diff --git a/src/accounting/currency/forms.py b/src/accounting/currency/forms.py
index f8cbff0..1f0bc3a 100644
--- a/src/accounting/currency/forms.py
+++ b/src/accounting/currency/forms.py
@@ -24,7 +24,7 @@ from flask_wtf import FlaskForm
 from wtforms import StringField, ValidationError
 from wtforms.validators import DataRequired, Regexp, NoneOf
 
-from accounting.database import db
+from accounting import db
 from accounting.locale import lazy_gettext
 from accounting.models import Currency
 from accounting.utils.strip_text import strip_text
diff --git a/src/accounting/currency/views.py b/src/accounting/currency/views.py
index ba76169..a6ee82b 100644
--- a/src/accounting/currency/views.py
+++ b/src/accounting/currency/views.py
@@ -23,7 +23,7 @@ from flask import Blueprint, render_template, redirect, session, request, \
     flash, url_for
 from werkzeug.datastructures import ImmutableMultiDict
 
-from accounting.database import db
+from accounting import db
 from accounting.locale import lazy_gettext
 from accounting.models import Currency
 from accounting.utils.next_url import inherit_next, or_next
diff --git a/src/accounting/database.py b/src/accounting/database.py
deleted file mode 100644
index 652763b..0000000
--- a/src/accounting/database.py
+++ /dev/null
@@ -1,39 +0,0 @@
-# The Mia! Accounting Flask Project.
-# Author: imacat@mail.imacat.idv.tw (imacat), 2023/1/25
-
-#  Copyright (c) 2023 imacat.
-#
-#  Licensed under the Apache License, Version 2.0 (the "License");
-#  you may not use this file except in compliance with the License.
-#  You may obtain a copy of the License at
-#
-#      http://www.apache.org/licenses/LICENSE-2.0
-#
-#  Unless required by applicable law or agreed to in writing, software
-#  distributed under the License is distributed on an "AS IS" BASIS,
-#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-#  See the License for the specific language governing permissions and
-#  limitations under the License.
-
-"""The database instance factory for the base account management.
-
-This is to overcome the problem that the database instance needs to be
-initialized at compile time, but as a submodule it is only available at run
-time.
-
-"""
-
-from flask_sqlalchemy import SQLAlchemy
-
-db: SQLAlchemy = SQLAlchemy()
-"""The database instance."""
-
-
-def set_db(new_db: SQLAlchemy) -> None:
-    """Sets the database instance.
-
-    :param new_db: The database instance.
-    :return: None.
-    """
-    global db
-    db = new_db
diff --git a/src/accounting/models.py b/src/accounting/models.py
index 942d54a..1371574 100644
--- a/src/accounting/models.py
+++ b/src/accounting/models.py
@@ -25,7 +25,7 @@ from flask import current_app
 from flask_babel import get_locale
 from sqlalchemy import text
 
-from accounting.database import db
+from accounting import db
 from accounting.utils.user import user_cls, user_pk_column
 
 
diff --git a/src/accounting/utils/random_id.py b/src/accounting/utils/random_id.py
index 9c4ecc0..fbb7835 100644
--- a/src/accounting/utils/random_id.py
+++ b/src/accounting/utils/random_id.py
@@ -22,7 +22,7 @@ This module should not import any other module from the application.
 import typing as t
 from secrets import randbelow
 
-from accounting.database import db
+from accounting import db
 
 
 def new_id(cls: t.Type):
diff --git a/tests/test_account.py b/tests/test_account.py
index 92b1090..88c6432 100644
--- a/tests/test_account.py
+++ b/tests/test_account.py
@@ -75,7 +75,7 @@ class AccountCommandTestCase(unittest.TestCase):
 
         runner: FlaskCliRunner = self.app.test_cli_runner()
         with self.app.app_context():
-            from accounting.database import db
+            from accounting import db
             from accounting.models import BaseAccount, Account, AccountL10n
             result: Result
             result = runner.invoke(args="init-db")
@@ -129,7 +129,7 @@ class AccountTestCase(unittest.TestCase):
 
         runner: FlaskCliRunner = self.app.test_cli_runner()
         with self.app.app_context():
-            from accounting.database import db
+            from accounting import db
             from accounting.models import BaseAccount, Account, AccountL10n
             result: Result
             result = runner.invoke(args="init-db")
@@ -316,7 +316,7 @@ class AccountTestCase(unittest.TestCase):
 
         :return: None.
         """
-        from accounting.database import db
+        from accounting import db
         from accounting.models import Account
         create_uri: str = f"{PREFIX}/create"
         store_uri: str = f"{PREFIX}/store"
@@ -648,7 +648,7 @@ class AccountTestCase(unittest.TestCase):
 
         :return: None.
         """
-        from accounting.database import db
+        from accounting import db
         from accounting.models import Account
         response: httpx.Response
 
diff --git a/tests/test_currency.py b/tests/test_currency.py
index df186dd..bd5710c 100644
--- a/tests/test_currency.py
+++ b/tests/test_currency.py
@@ -71,7 +71,7 @@ class CurrencyCommandTestCase(unittest.TestCase):
 
         runner: FlaskCliRunner = self.app.test_cli_runner()
         with self.app.app_context():
-            from accounting.database import db
+            from accounting import db
             from accounting.models import Currency, CurrencyL10n
             result: Result
             result = runner.invoke(args="init-db")
@@ -128,7 +128,7 @@ class CurrencyTestCase(unittest.TestCase):
 
         runner: FlaskCliRunner = self.app.test_cli_runner()
         with self.app.app_context():
-            from accounting.database import db
+            from accounting import db
             from accounting.models import Currency, CurrencyL10n
             result: Result
             result = runner.invoke(args="init-db")