feat: 添加购买分组功能，替代跨分类购物选项

backend/internal/models/category.go

@@ -7,23 +7,24 @@ import (
 )
 
 type Category struct {
-	ID                 uint           `gorm:"primaryKey" json:"id"`
-	Name               string         `gorm:"size:100;not null;uniqueIndex" json:"name"`
-	Description        string         `json:"description"`
-	ParentID           *uint          `json:"parent_id"`
-	MinAmount          *float64       `json:"min_amount"`
-	MaxAmount          *float64       `json:"max_amount"`
-	MinQuantity        *int           `json:"min_quantity"`
-	MaxQuantity        *int           `json:"max_quantity"`
-	MinWeight          *float64       `json:"min_weight"`
-	MaxWeight          *float64       `json:"max_weight"`
-	AllowCrossCategory bool           `gorm:"default:false" json:"allow_cross_category"`
-	SortOrder          int            `gorm:"default:0" json:"sort_order"`
-	CreatedAt          time.Time      `json:"created_at"`
-	UpdatedAt          time.Time      `json:"updated_at"`
-	DeletedAt          gorm.DeletedAt `gorm:"index" json:"-"`
-	ProductCount       int64          `gorm:"-" json:"product_count"`
-	Children           []Category     `gorm:"foreignKey:ParentID" json:"children,omitempty"`
+	ID               uint           `gorm:"primaryKey" json:"id"`
+	Name             string         `gorm:"size:100;not null;uniqueIndex" json:"name"`
+	Description      string         `json:"description"`
+	ParentID         *uint          `json:"parent_id"`
+	PurchaseGroupID  *uint          `json:"purchase_group_id"`
+	PurchaseGroup    *PurchaseGroup `gorm:"foreignKey:PurchaseGroupID" json:"purchase_group,omitempty"`
+	MinAmount        *float64       `json:"min_amount"`
+	MaxAmount        *float64       `json:"max_amount"`
+	MinQuantity      *int           `json:"min_quantity"`
+	MaxQuantity      *int           `json:"max_quantity"`
+	MinWeight        *float64       `json:"min_weight"`
+	MaxWeight        *float64       `json:"max_weight"`
+	SortOrder        int            `gorm:"default:0" json:"sort_order"`
+	CreatedAt        time.Time      `json:"created_at"`
+	UpdatedAt        time.Time      `json:"updated_at"`
+	DeletedAt        gorm.DeletedAt `gorm:"index" json:"-"`
+	ProductCount     int64          `gorm:"-" json:"product_count"`
+	Children         []Category     `gorm:"foreignKey:ParentID" json:"children,omitempty"`
 }
 
 func (Category) TableName() string {

backend/internal/models/purchase_group.go

@@ -0,0 +1,22 @@
+package models
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+)
+
+type PurchaseGroup struct {
+	ID          uint           `gorm:"primaryKey" json:"id"`
+	Name        string         `gorm:"size:100;not null;uniqueIndex" json:"name"`
+	Description string         `json:"description"`
+	SortOrder   int            `gorm:"default:0" json:"sort_order"`
+	CreatedAt   time.Time      `json:"created_at"`
+	UpdatedAt   time.Time      `json:"updated_at"`
+	DeletedAt   gorm.DeletedAt `gorm:"index" json:"-"`
+	Categories  []Category     `gorm:"foreignKey:PurchaseGroupID" json:"categories,omitempty"`
+}
+
+func (PurchaseGroup) TableName() string {
+	return "purchase_groups"
+}