diff --git a/internal/howmuch/model/event.go b/internal/howmuch/model/event.go
index b4ce516..ecd866b 100644
--- a/internal/howmuch/model/event.go
+++ b/internal/howmuch/model/event.go
@@ -25,7 +25,8 @@ package model
 import "time"
 
 type Event struct {
-	ID              int
+	ID int
+
 	Name            string
 	Description     string
 	Users           []*User
@@ -33,6 +34,7 @@ type Event struct {
 	TotalAmount     Money
 	DefaultCurrency Currency
 	CreatedBy       User
-	CreatedAt       time.Time
-	UpdatedAt       time.Time
+
+	CreatedAt time.Time
+	UpdatedAt time.Time
 }
diff --git a/internal/howmuch/model/expense.go b/internal/howmuch/model/expense.go
index 862bfdd..7515fad 100644
--- a/internal/howmuch/model/expense.go
+++ b/internal/howmuch/model/expense.go
@@ -30,13 +30,15 @@ type ExpenseDetail struct {
 }
 
 type Expense struct {
-	ID           int
+	ID int
+
 	Amount       Money
 	Currency     Currency
 	PayerIDs     []int
 	RecipientIDs []int
 	EventID      int
 	Detail       ExpenseDetail
-	CreatedAt    time.Time
-	UpdatedAt    time.Time
+
+	CreatedAt time.Time
+	UpdatedAt time.Time
 }
diff --git a/internal/howmuch/model/participation.go b/internal/howmuch/model/participation.go
new file mode 100644
index 0000000..1f215d4
--- /dev/null
+++ b/internal/howmuch/model/participation.go
@@ -0,0 +1,37 @@
+// MIT License
+//
+// Copyright (c) 2024 vinchent <vinchent@vinchent.xyz>
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+package model
+
+import "time"
+
+// Participation is the association between Users and Events
+type Participation struct {
+	ID int
+
+	UserID          int
+	EventID         int
+	InvitedByUserID int
+
+	CreatedAt time.Time
+	UpdatedAt time.Time
+}
diff --git a/internal/howmuch/model/transaction.go b/internal/howmuch/model/transaction.go
new file mode 100644
index 0000000..8f0fada
--- /dev/null
+++ b/internal/howmuch/model/transaction.go
@@ -0,0 +1,38 @@
+// MIT License
+//
+// Copyright (c) 2024 vinchent <vinchent@vinchent.xyz>
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+package model
+
+import "time"
+
+// Transaction is the association between Expenses and Users
+type Transaction struct {
+	ID int
+
+	ExpenseID Expense
+	PayerID   int
+	Amount    Money
+	Currency  Currency
+
+	CreatedAt time.Time
+	UpdatedAt time.Time
+}
diff --git a/internal/howmuch/model/user.go b/internal/howmuch/model/user.go
index 14f3387..c6e7fd8 100644
--- a/internal/howmuch/model/user.go
+++ b/internal/howmuch/model/user.go
@@ -38,11 +38,13 @@ type UserExistDTO struct {
 
 // User model
 type User struct {
-	ID        int
+	ID int
+
 	Email     string
 	FirstName string
 	LastName  string
 	Password  string
+
 	CreatedAt time.Time
 	UpdatedAt time.Time
 }