解决Mongoose Schema向MongoDB存储空数组的问题

问题背景 #

我使用Express + Node.js开发API，通过Mongoose将数据存储到MongoDB，设计的MessagesSchema如下：

const MessagesSchema = new mongoose.Schema(
  {
    readReceipt: {
      type: String,
      required: [true, "Read Receipt Mandatory"],
      enum: {
        values: ["sent", "received", "read"],
        message: `Invalid value {VALUE}`,
      },
    },
    messageContent: { type: String },
    sentBy: {
      type: mongoose.Schema.Types.ObjectId,
      ref: "Users",
      required: [true, "Sender cannot be Empty"],
    },
    sentTo: {
      type: [mongoose.Schema.Types.ObjectId],
      ref: "Users",
      required: [true, "At Least One senderId required"],
    },
  },
  { timestamps: true }
);

但实际存入数据库的数据中，sentTo字段为空数组却未触发必填验证：

{
    "readReceipt": "sent",
    "messageContent": "Test Message 4",
    "sentBy": "6728a8b1b6fd6ebeac8e0fa5",
    "sentTo": [],
    "_id": "672b2539d7f2f99e8f9ef738",
    "createdAt": "2024-11-06T08:13:45.080Z",
    "updatedAt": "2024-11-06T08:13:45.080Z",
    "__v": 0
}

使用版本：

• mongoose: "8.8.0"
• express: "4.21.1"
• node: "18.18.0"

核心原因 #

Mongoose中required: true对数组类型仅验证数组本身存在，空数组属于合法存在的数组，因此不会触发报错。要限制数组不能为空，需额外添加验证规则。

可行解决方案 #

方案1：使用minLength验证规则 #

直接在sentTo字段配置中添加minLength，指定数组最小长度为1：

sentTo: {
  type: [mongoose.Schema.Types.ObjectId],
  ref: "Users",
  required: [true, "At Least One senderId required"],
  minLength: [1, "At Least One recipient required"]
}

方案2：自定义验证函数 #

如果需要更灵活的验证逻辑，可使用自定义验证器：

sentTo: {
  type: [mongoose.Schema.Types.ObjectId],
  ref: "Users",
  required: [true, "At Least One senderId required"],
  validate: {
    validator: function(v) {
      return v.length > 0;
    },
    message: "At Least One recipient required"
  }
}

方案3：结合required与default（可选） #

设置default: undefined避免Mongoose自动给数组填充空默认值，配合required强制传入非空数组：

sentTo: {
  type: [mongoose.Schema.Types.ObjectId],
  ref: "Users",
  required: [true, "At Least One senderId required"],
  default: undefined
}

注意：若数据库中已存在空数组的历史数据，修改Schema后需手动清理或在更新时触发验证逻辑。

内容的提问来源于stack exchange，提问作者y.d_edition