Add Expense entity to database

db/db.go

@@ -58,5 +58,6 @@ func Connect() *gorm.DB {
 	gormDB.AutoMigrate(&User{})
 	gormDB.AutoMigrate(&Type{})
 	gormDB.AutoMigrate(&Session{})
+	gormDB.AutoMigrate(&Expense{})
 	return newUDB
 }

db/expense.go

@@ -0,0 +1,136 @@
+package db
+
+import (
+	"errors"
+	"log"
+	"time"
+
+	"gorm.io/gorm"
+)
+
+type Expense struct {
+	gorm.Model
+	CardID  uint
+	Card    *Card
+	Value   uint64
+	Comment string
+	Date    time.Time
+	UserID  uint
+	User    *User
+	TypeID  uint
+	Type    *Type
+}
+
+// Implements db.UserIdentifiable:1
+func (e Expense) GetID() uint {
+	return e.ID
+}
+
+// Implements db.UserIdentifiable:2
+func (e Expense) GetUserID() uint {
+	return e.UserID
+}
+
+// Implements db.UserIdentifiable:3
+func (e *Expense) SetUserID(id uint) {
+	e.UserID = id
+}
+
+var (
+	ERROR_EXPENSE_INVALID_USERID            = errors.New("Expense's `UserID` and Card's `UserID` are not equal")
+	ERROR_EXPENSE_CARD_INSUFFICIENT_BALANCE = errors.New("Card's `Balance` is lower than Expense's Value")
+	ERROR_EXPENSE_INVALID_TYPE_USERID       = errors.New("Expense's `UserID` and Type's `UserID` are not equal")
+)
+
+func (e *Expense) BeforeCreate(tx *gorm.DB) error {
+	log.Printf("BeforeCreate")
+	card := &Card{}
+	if err := tx.Find(card, e.CardID).Error; err != nil {
+		return err
+	}
+	if card.UserID != e.UserID {
+		return ERROR_EXPENSE_INVALID_USERID
+	}
+	if card.Balance < e.Value {
+		return ERROR_EXPENSE_CARD_INSUFFICIENT_BALANCE
+	}
+	card.Balance -= e.Value
+	if err := tx.Save(card).Error; err != nil {
+		return err
+	}
+
+	typ := &Type{}
+	if err := tx.Find(typ, e.TypeID).Error; err != nil {
+		return err
+	}
+	log.Printf("e.UserID = %d\n", e.UserID)
+	log.Printf("e.TypeID= %d\n", e.TypeID)
+	log.Printf("typ.UserID= %d\n", typ.UserID)
+	if typ.UserID != e.UserID {
+		return ERROR_EXPENSE_INVALID_TYPE_USERID
+	}
+	return nil
+}
+
+func (e *Expense) BeforeUpdate(tx *gorm.DB) (err error) {
+	var original Expense
+	if err := tx.Model(&Expense{}).Select("card_id", "value").Where("id = ?", e.ID).First(&original).Error; err != nil {
+		return err
+	}
+	if original.CardID != 0 {
+		oldCard := &Card{}
+		if err := tx.Find(oldCard, original.CardID).Error; err != nil {
+			return err
+		}
+		if oldCard.UserID != e.UserID {
+			return ERROR_EXPENSE_INVALID_USERID
+		}
+		oldCard.Balance += e.Value
+		if err := tx.Save(oldCard).Error; err != nil {
+			return err
+		}
+	}
+
+	if e.CardID != 0 {
+		newCard := &Card{}
+		if err := tx.Find(newCard, e.CardID).Error; err != nil {
+			return err
+		}
+		if newCard.UserID != e.UserID {
+			return ERROR_EXPENSE_INVALID_USERID
+		}
+		if newCard.Balance < e.Value {
+			return ERROR_EXPENSE_CARD_INSUFFICIENT_BALANCE
+		}
+		newCard.Balance -= e.Value
+		if err := tx.Save(newCard).Error; err != nil {
+			return err
+		}
+	}
+	typ := &Type{}
+	if err := tx.Find(typ, e.TypeID).Error; err != nil {
+		return err
+	}
+	if typ.UserID != e.UserID {
+		return ERROR_EXPENSE_INVALID_TYPE_USERID
+	}
+	return nil
+}
+
+func (e *Expense) AfterDelete(tx *gorm.DB) (err error) {
+	card := &Card{}
+	if err := tx.Find(card, e.CardID).Error; err != nil {
+		return err
+	}
+	if card.UserID != e.UserID {
+		return ERROR_EXPENSE_INVALID_USERID
+	}
+	if card.Balance < e.Value {
+		return ERROR_EXPENSE_CARD_INSUFFICIENT_BALANCE
+	}
+	card.Balance += e.Value
+	if err := tx.Save(card).Error; err != nil {
+		return err
+	}
+	return nil
+}