Add comment functionality.

server/model/comment.go

@@ -0,0 +1,31 @@
+package model
+
+import (
+	"gorm.io/gorm"
+	"time"
+)
+
+type Comment struct {
+	gorm.Model
+	Content    string   `gorm:"not null"`
+	ResourceID uint     `gorm:"not null"`
+	UserID     uint     `gorm:"not null"`
+	User       User     `gorm:"foreignKey:UserID"`
+	Resource   Resource `gorm:"foreignKey:ResourceID"`
+}
+
+type CommentView struct {
+	ID        uint      `json:"id"`
+	Content   string    `json:"content"`
+	CreatedAt time.Time `json:"created_at"`
+	User      UserView  `json:"user"`
+}
+
+func (c *Comment) ToView() *CommentView {
+	return &CommentView{
+		ID:        c.ID,
+		Content:   c.Content,
+		CreatedAt: c.CreatedAt,
+		User:      c.User.ToView(),
+	}
+}