diff --git a/src/accounting/report/reports.py b/src/accounting/report/reports.py
index 8ba07c3..1359f3a 100644
--- a/src/accounting/report/reports.py
+++ b/src/accounting/report/reports.py
@@ -27,13 +27,14 @@ from flask_sqlalchemy.query import Query
 
 from accounting import db
 from accounting.models import JournalEntry, Transaction, Account, Currency
-from accounting.transaction.dispatcher import TXN_TYPE_OBJ, TransactionTypes
 from accounting.utils.pagination import Pagination
+from accounting.utils.txn_types import TransactionTypeEnum
 from .period import Period
 from .period_choosers import PeriodChooser, \
     JournalPeriodChooser
 from .report_chooser import ReportChooser, ReportType
 from .report_rows import ReportRow, JournalRow
+import typing as t
 
 
 class JournalEntryReport(ABC):
@@ -104,12 +105,12 @@ class JournalEntryReport(ABC):
         """
 
     @property
-    def txn_types(self) -> TransactionTypes:
+    def txn_types(self) -> t.Type[TransactionTypeEnum]:
         """Returns the transaction types.
 
         :return: The transaction types.
         """
-        return TXN_TYPE_OBJ
+        return TransactionTypeEnum
 
     def as_csv_download(self) -> Response:
         """Returns the journal entries as CSV download.
diff --git a/src/accounting/templates/accounting/include/add-txn-material-fab.html b/src/accounting/templates/accounting/include/add-txn-material-fab.html
index 8816eb2..80b3cb5 100644
--- a/src/accounting/templates/accounting/include/add-txn-material-fab.html
+++ b/src/accounting/templates/accounting/include/add-txn-material-fab.html
@@ -22,13 +22,13 @@ First written: 2023/2/25
 {% if accounting_can_edit() %}
   <div id="accounting-material-fab-speed-dial" class="d-md-none accounting-material-fab">
     <div id="accounting-material-fab-speed-dial-actions" class="d-md-none accounting-material-fab-speed-dial-group">
-      <a class="btn rounded-pill" href="{{ url_for("accounting.transaction.create", txn_type=types.expense)|accounting_append_next }}">
+      <a class="btn rounded-pill" href="{{ url_for("accounting.transaction.create", txn_type=txn_types.CASH_EXPENSE)|accounting_append_next }}">
         {{ A_("Cash expense") }}
       </a>
-      <a class="btn rounded-pill" href="{{ url_for("accounting.transaction.create", txn_type=types.income)|accounting_append_next }}">
+      <a class="btn rounded-pill" href="{{ url_for("accounting.transaction.create", txn_type=txn_types.CASH_INCOME)|accounting_append_next }}">
         {{ A_("Cash income") }}
       </a>
-      <a class="btn rounded-pill" href="{{ url_for("accounting.transaction.create", txn_type=types.transfer)|accounting_append_next }}">
+      <a class="btn rounded-pill" href="{{ url_for("accounting.transaction.create", txn_type=txn_types.TRANSFER)|accounting_append_next }}">
         {{ A_("Transfer") }}
       </a>
     </div>
diff --git a/src/accounting/templates/accounting/report/journal.html b/src/accounting/templates/accounting/report/journal.html
index fb506d1..2c62dfe 100644
--- a/src/accounting/templates/accounting/report/journal.html
+++ b/src/accounting/templates/accounting/report/journal.html
@@ -40,16 +40,16 @@ First written: 2023/3/4
       </button>
       <ul class="dropdown-menu">
         <li>
-          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=report.txn_types.expense)|accounting_append_next }}">
+          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=report.txn_types.CASH_EXPENSE)|accounting_append_next }}">
             {{ A_("Cash Expense") }}</a>
         </li>
         <li>
-          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=report.txn_types.income)|accounting_append_next }}">
+          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=report.txn_types.CASH_INCOME)|accounting_append_next }}">
             {{ A_("Cash Income") }}
           </a>
         </li>
         <li>
-          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=report.txn_types.transfer)|accounting_append_next }}">
+          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=report.txn_types.TRANSFER)|accounting_append_next }}">
             {{ A_("Transfer") }}
           </a>
         </li>
@@ -69,7 +69,7 @@ First written: 2023/3/4
   </a>
 </div>
 
-{% with types = report.txn_types %}
+{% with txn_types = report.txn_types %}
   {% include "accounting/include/add-txn-material-fab.html" %}
 {% endwith %}
 
diff --git a/src/accounting/templates/accounting/transaction/list.html b/src/accounting/templates/accounting/transaction/list.html
index e212287..61d3e60 100644
--- a/src/accounting/templates/accounting/transaction/list.html
+++ b/src/accounting/templates/accounting/transaction/list.html
@@ -38,16 +38,16 @@ First written: 2023/2/18
       </button>
       <ul class="dropdown-menu">
         <li>
-          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=types.expense)|accounting_append_next }}">
+          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=txn_types.CASH_EXPENSE)|accounting_append_next }}">
             {{ A_("Cash Expense") }}</a>
         </li>
         <li>
-          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=types.income)|accounting_append_next }}">
+          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=txn_types.CASH_INCOME)|accounting_append_next }}">
             {{ A_("Cash Income") }}
           </a>
         </li>
         <li>
-          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=types.transfer)|accounting_append_next }}">
+          <a class="dropdown-item" href="{{ url_for("accounting.transaction.create", txn_type=txn_types.TRANSFER)|accounting_append_next }}">
             {{ A_("Transfer") }}
           </a>
         </li>
diff --git a/src/accounting/transaction/converters.py b/src/accounting/transaction/converters.py
index 37eaeae..11bf80c 100644
--- a/src/accounting/transaction/converters.py
+++ b/src/accounting/transaction/converters.py
@@ -24,8 +24,7 @@ from werkzeug.routing import BaseConverter
 
 from accounting import db
 from accounting.models import Transaction
-from accounting.transaction.dispatcher import TransactionType, \
-    TXN_TYPE_DICT
+from accounting.utils.txn_types import TransactionTypeEnum
 
 
 class TransactionConverter(BaseConverter):
@@ -56,24 +55,26 @@ class TransactionTypeConverter(BaseConverter):
     """The transaction converter to convert the transaction type ID from and to
     the corresponding transaction type in the routes."""
 
-    def to_python(self, value: str) -> TransactionType:
+    def to_python(self, value: str) -> TransactionTypeEnum:
         """Converts a transaction ID to a transaction.
 
         :param value: The transaction ID.
         :return: The corresponding transaction.
         """
-        txn_type: TransactionType | None = TXN_TYPE_DICT.get(value)
+        type_dict: dict[str, TransactionTypeEnum] \
+            = {x.value: x for x in TransactionTypeEnum}
+        txn_type: TransactionTypeEnum | None = type_dict.get(value)
         if txn_type is None:
             abort(404)
         return txn_type
 
-    def to_url(self, value: TransactionType) -> str:
+    def to_url(self, value: TransactionTypeEnum) -> str:
         """Converts a transaction type to its ID.
 
         :param value: The transaction type.
         :return: The ID.
         """
-        return str(value.ID)
+        return str(value.value)
 
 
 class DateConverter(BaseConverter):
diff --git a/src/accounting/transaction/dispatcher.py b/src/accounting/transaction/dispatcher.py
index 237ff53..f433ca6 100644
--- a/src/accounting/transaction/dispatcher.py
+++ b/src/accounting/transaction/dispatcher.py
@@ -24,15 +24,14 @@ from flask import render_template, request, abort
 from flask_wtf import FlaskForm
 
 from accounting.models import Transaction
+from accounting.template_globals import default_currency_code
+from accounting.utils.txn_types import TransactionTypeEnum
 from .forms import TransactionForm, IncomeTransactionForm, \
     ExpenseTransactionForm, TransferTransactionForm
-from accounting.template_globals import default_currency_code
 
 
 class TransactionType(ABC):
     """An abstract transaction type."""
-    ID: str = ""
-    """The transaction type ID."""
     CHECK_ORDER: int = -1
     """The order when checking the transaction type."""
 
@@ -93,8 +92,6 @@ class TransactionType(ABC):
 
 class IncomeTransaction(TransactionType):
     """An income transaction."""
-    ID: str = "income"
-    """The transaction type ID."""
     CHECK_ORDER: int = 2
     """The order when checking the transaction type."""
 
@@ -113,7 +110,8 @@ class IncomeTransaction(TransactionType):
         :return: the form to create a transaction.
         """
         return render_template("accounting/transaction/income/create.html",
-                               form=form, txn_type=self,
+                               form=form,
+                               txn_type=TransactionTypeEnum.CASH_INCOME,
                                currency_template=self.__currency_template,
                                entry_template=self._entry_template)
 
@@ -163,8 +161,6 @@ class IncomeTransaction(TransactionType):
 
 class ExpenseTransaction(TransactionType):
     """An expense transaction."""
-    ID: str = "expense"
-    """The transaction type ID."""
     CHECK_ORDER: int = 1
     """The order when checking the transaction type."""
 
@@ -183,7 +179,8 @@ class ExpenseTransaction(TransactionType):
         :return: the form to create a transaction.
         """
         return render_template("accounting/transaction/expense/create.html",
-                               form=form, txn_type=self,
+                               form=form,
+                               txn_type=TransactionTypeEnum.CASH_EXPENSE,
                                currency_template=self.__currency_template,
                                entry_template=self._entry_template)
 
@@ -233,8 +230,6 @@ class ExpenseTransaction(TransactionType):
 
 class TransferTransaction(TransactionType):
     """A transfer transaction."""
-    ID: str = "transfer"
-    """The transaction type ID."""
     CHECK_ORDER: int = 3
     """The order when checking the transaction type."""
 
@@ -253,7 +248,8 @@ class TransferTransaction(TransactionType):
         :return: the form to create a transaction.
         """
         return render_template("accounting/transaction/transfer/create.html",
-                               form=form, txn_type=self,
+                               form=form,
+                               txn_type=TransactionTypeEnum.TRANSFER,
                                currency_template=self.__currency_template,
                                entry_template=self._entry_template)
 
@@ -301,44 +297,28 @@ class TransferTransaction(TransactionType):
             debit_total="-", credit_total="-")
 
 
-class TransactionTypes:
-    """The transaction types, as object properties."""
-
-    def __init__(self, income: IncomeTransaction, expense: ExpenseTransaction,
-                 transfer: TransferTransaction):
-        """Constructs the transaction types as object properties.
-
-        :param income: The income transaction type.
-        :param expense: The expense transaction type.
-        :param transfer: The transfer transaction type.
-        """
-        self.income: IncomeTransaction = income
-        self.expense: ExpenseTransaction = expense
-        self.transfer: TransferTransaction = transfer
+TXN_ENUM_TO_OP: dict[TransactionTypeEnum, TransactionType] \
+    = {TransactionTypeEnum.CASH_INCOME: IncomeTransaction(),
+       TransactionTypeEnum.CASH_EXPENSE: ExpenseTransaction(),
+       TransactionTypeEnum.TRANSFER: TransferTransaction()}
+"""The map from the transaction type enum to its operator."""
 
 
-TXN_TYPE_DICT: dict[str, TransactionType] \
-    = {x.ID: x() for x in {IncomeTransaction,
-                           ExpenseTransaction,
-                           TransferTransaction}}
-"""The transaction types, as a dictionary."""
-TXN_TYPE_OBJ: TransactionTypes = TransactionTypes(**TXN_TYPE_DICT)
-"""The transaction types, as an object."""
-
-
-def get_txn_type(txn: Transaction) -> TransactionType:
-    """Returns the transaction type that may be specified in the "as" query
-    parameter.  If it is not specified, check the transaction type from the
-    transaction.
+def get_txn_type_op(txn: Transaction) -> TransactionType:
+    """Returns the transaction type operator that may be specified in the "as"
+    query parameter.  If it is not specified, check the transaction type from
+    the transaction.
 
     :param txn: The transaction.
     :return: None.
     """
     if "as" in request.args:
-        if request.args["as"] not in TXN_TYPE_DICT:
+        type_dict: dict[str, TransactionTypeEnum] \
+            = {x.value: x for x in TransactionTypeEnum}
+        if request.args["as"] not in type_dict:
             abort(404)
-        return TXN_TYPE_DICT[request.args["as"]]
-    for txn_type in sorted(TXN_TYPE_DICT.values(),
+        return TXN_ENUM_TO_OP[type_dict[request.args["as"]]]
+    for txn_type in sorted(TXN_ENUM_TO_OP.values(),
                            key=lambda x: x.CHECK_ORDER):
         if txn_type.is_my_type(txn):
             return txn_type
diff --git a/src/accounting/transaction/views.py b/src/accounting/transaction/views.py
index 27831a5..ddc72fe 100644
--- a/src/accounting/transaction/views.py
+++ b/src/accounting/transaction/views.py
@@ -32,8 +32,9 @@ from accounting.utils.flash_errors import flash_form_errors
 from accounting.utils.next_uri import inherit_next, or_next
 from accounting.utils.pagination import Pagination
 from accounting.utils.permission import has_permission, can_view, can_edit
+from accounting.utils.txn_types import TransactionTypeEnum
 from accounting.utils.user import get_current_user_pk
-from .dispatcher import TransactionType, get_txn_type, TXN_TYPE_OBJ
+from .dispatcher import TransactionType, TXN_ENUM_TO_OP, get_txn_type_op
 from .forms import sort_transactions_in, TransactionReorderForm
 from .queries import get_transaction_query
 from .template_filters import with_type, to_transfer, format_amount_input, \
@@ -59,37 +60,39 @@ def list_transactions() -> str:
     pagination: Pagination = Pagination[Transaction](transactions)
     return render_template("accounting/transaction/list.html",
                            list=pagination.list, pagination=pagination,
-                           types=TXN_TYPE_OBJ)
+                           txn_types=TransactionTypeEnum)
 
 
 @bp.get("/create/<transactionType:txn_type>", endpoint="create")
 @has_permission(can_edit)
-def show_add_transaction_form(txn_type: TransactionType) -> str:
+def show_add_transaction_form(txn_type: TransactionTypeEnum) -> str:
     """Shows the form to add a transaction.
 
     :param txn_type: The transaction type.
     :return: The form to add a transaction.
     """
-    form: txn_type.form
+    txn_type_op: TransactionType = TXN_ENUM_TO_OP[txn_type]
+    form: txn_type_op.form
     if "form" in session:
-        form = txn_type.form(ImmutableMultiDict(parse_qsl(session["form"])))
+        form = txn_type_op.form(ImmutableMultiDict(parse_qsl(session["form"])))
         del session["form"]
         form.validate()
     else:
-        form = txn_type.form()
-    return txn_type.render_create_template(form)
+        form = txn_type_op.form()
+    return txn_type_op.render_create_template(form)
 
 
 @bp.post("/store/<transactionType:txn_type>", endpoint="store")
 @has_permission(can_edit)
-def add_transaction(txn_type: TransactionType) -> redirect:
+def add_transaction(txn_type: TransactionTypeEnum) -> redirect:
     """Adds a transaction.
 
     :param txn_type: The transaction type.
     :return: The redirection to the transaction detail on success, or the
         transaction creation form on error.
     """
-    form: txn_type.form = txn_type.form(request.form)
+    txn_type_op: TransactionType = TXN_ENUM_TO_OP[txn_type]
+    form: txn_type_op.form = txn_type_op.form(request.form)
     if not form.validate():
         flash_form_errors(form)
         session["form"] = urlencode(list(request.form.items()))
@@ -111,8 +114,8 @@ def show_transaction_detail(txn: Transaction) -> str:
     :param txn: The transaction.
     :return: The detail.
     """
-    txn_type: TransactionType = get_txn_type(txn)
-    return txn_type.render_detail_template(txn)
+    txn_type_op: TransactionType = get_txn_type_op(txn)
+    return txn_type_op.render_detail_template(txn)
 
 
 @bp.get("/<transaction:txn>/edit", endpoint="edit")
@@ -123,15 +126,15 @@ def show_transaction_edit_form(txn: Transaction) -> str:
     :param txn: The transaction.
     :return: The form to edit the transaction.
     """
-    txn_type: TransactionType = get_txn_type(txn)
-    form: txn_type.form
+    txn_type_op: TransactionType = get_txn_type_op(txn)
+    form: txn_type_op.form
     if "form" in session:
-        form = txn_type.form(ImmutableMultiDict(parse_qsl(session["form"])))
+        form = txn_type_op.form(ImmutableMultiDict(parse_qsl(session["form"])))
         del session["form"]
         form.validate()
     else:
-        form = txn_type.form(obj=txn)
-    return txn_type.render_edit_template(txn, form)
+        form = txn_type_op.form(obj=txn)
+    return txn_type_op.render_edit_template(txn, form)
 
 
 @bp.post("/<transaction:txn>/update", endpoint="update")
@@ -143,8 +146,8 @@ def update_transaction(txn: Transaction) -> redirect:
     :return: The redirection to the transaction detail on success, or the
         transaction edit form on error.
     """
-    txn_type: TransactionType = get_txn_type(txn)
-    form: txn_type.form = txn_type.form(request.form)
+    txn_type_op: TransactionType = get_txn_type_op(txn)
+    form: txn_type_op.form = txn_type_op.form(request.form)
     if not form.validate():
         flash_form_errors(form)
         session["form"] = urlencode(list(request.form.items()))
diff --git a/src/accounting/utils/txn_types.py b/src/accounting/utils/txn_types.py
new file mode 100644
index 0000000..6da6e50
--- /dev/null
+++ b/src/accounting/utils/txn_types.py
@@ -0,0 +1,30 @@
+# The Mia! Accounting Flask Project.
+# Author: imacat@mail.imacat.idv.tw (imacat), 2023/3/4
+
+#  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 transaction types.
+
+"""
+from enum import Enum
+
+
+class TransactionTypeEnum(Enum):
+    """The transaction types."""
+    CASH_INCOME: str = "income"
+    """The cash income transaction."""
+    CASH_EXPENSE: str = "expense"
+    """The cash expense transaction."""
+    TRANSFER: str = "transfer"
+    """The transfer transaction."""