Javascript Mongoose要求唯一，如果存在，请修改并保存

我需要保持我的slug的唯一性，但是如果默认情况下它们会创建相同的slug，我仍然希望接受新条目

例如，列出杂货店：

输入：

[
  {
    "name": "Grocery Store",
    "location": "Bellevue"
  },
  {
    "name": "Grocery Store",
    "location": "Seattle"
  },
  {
    "name": "Grocery Store",
    "location": "Seattle"
  },
  {
    "name": "Grocery Store",
    "location": "Seattle"
  }
]

另存为：

[
  {
    "name": "Grocery Store",
    "location": "Bellevue",
    "slug": "grocery-store-bellevue"
  },
  {
    "name": "Grocery Store",
    "location": "Seattle",
    "slug": "grocery-store-seattle"
  },
  {
    "name": "Grocery Store",
    "location": "Seattle",
    "slug": "grocery-store-seattle-1"
  },
  {
    "name": "Grocery Store",
    "location": "Seattle",
    "slug": "grocery-store-seattle-2"
  }
]

需要slug的模式：

slug: {
  type: String,
  unique: true
},

我的pre（'save'）…截至目前

// Create project slug from name and location
StoreSchema.pre('save', function(next) {
  this.slug = slugify(this.name + '-' + this.location, { lower: true });

  next();
});