Add collection api.

server/model/collection.go

@@ -0,0 +1,31 @@
+package model
+
+import "gorm.io/gorm"
+
+type Collection struct {
+	gorm.Model
+	Title     string     `gorm:"not null"`
+	Article   string     `gorm:"not null"`
+	UserID    uint       `gorm:"not null"`
+	User      User       `gorm:"foreignKey:UserID;references:ID"`
+	Images    []Image    `gorm:"many2many:collection_images;"`
+	Resources []Resource `gorm:"many2many:collection_resources;"`
+}
+
+type CollectionView struct {
+	ID      uint     `json:"id"`
+	Title   string   `json:"title"`
+	Article string   `json:"article"`
+	User    UserView `json:"user"`
+	Images  []Image  `json:"images"`
+}
+
+func (c Collection) ToView() *CollectionView {
+	return &CollectionView{
+		ID:      c.ID,
+		Title:   c.Title,
+		Article: c.Article,
+		User:    c.User.ToView(),
+		Images:  c.Images,
+	}
+}