如何用findOne、Find方法获取MongoDB中MembersID数组元素值

问题背景 #

已定义Mongoose Schema如下：

const { model, Schema} = require("mongoose")

let ticketSchema = new Schema({
    GuildID : String,
    MembersID: [String],
    TicketID: String,
    ChannelID: String,
    Closed: Boolean,
    Locked: Boolean,
    Type: String,
    Claimed: Boolean,
    ClaimedBy: String,
    Open:Boolean,
    OpenBy:String,
})

module.exports = model("Ticket", ticketSchema);

示例文档结构：

{
  _id: new ObjectId("63d8340e0a415466f7ad55f0"),
  GuildID: '1066373193767592047',
  MembersID: ['811664013313310720'],
  TicketID: '2',
  ChannelID: '1069728239200780398',
  Closed: false,
  Locked: false,
  Type: 'Hola',
  Claimed: false,
  Open: false,
  OpenBy: '811664013313310720',
  __v: 0
}

需要获取MembersID数组的第一个元素用于系统校验，以下是两种实现方案：

方案1：使用findOne方法 #

findOne用于匹配单个目标文档，获取文档后直接通过数组索引取首个元素：

const Ticket = require('./path-to-your-ticket-model');

// 可根据业务需求替换查询条件，比如GuildID、ChannelID等
async function getFirstMemberId() {
  try {
    const ticketDoc = await Ticket.findOne({ TicketID: '2' });
    
    if (ticketDoc && ticketDoc.MembersID.length > 0) {
      const firstMemberId = ticketDoc.MembersID[0];
      // 此处将firstMemberId用于系统校验逻辑
      console.log(firstMemberId);
      return firstMemberId;
    } else {
      console.log('未找到目标文档或MembersID数组为空');
      return null;
    }
  } catch (error) {
    console.error('查询失败:', error);
    throw error;
  }
}

// 调用函数执行查询
getFirstMemberId();

方案2：使用find方法 #

find返回匹配的文档数组，需先取数组中的目标文档，再提取MembersID的首个元素：

const Ticket = require('./path-to-your-ticket-model');

async function getFirstMemberId() {
  try {
    const ticketDocs = await Ticket.find({ TicketID: '2' });
    
    if (ticketDocs.length > 0) {
      const targetDoc = ticketDocs[0];
      if (targetDoc.MembersID.length > 0) {
        const firstMemberId = targetDoc.MembersID[0];
        // 此处将firstMemberId用于系统校验逻辑
        console.log(firstMemberId);
        return firstMemberId;
      } else {
        console.log('MembersID数组为空');
        return null;
      }
    } else {
      console.log('未找到匹配的文档');
      return null;
    }
  } catch (error) {
    console.error('查询失败:', error);
    throw error;
  }
}

// 调用函数执行查询
getFirstMemberId();

优化：数据库层面投影返回指定内容 #

如果希望减少数据传输量，可使用投影（Projection）让数据库仅返回MembersID的第一个元素：

// findOne搭配投影
const ticketDoc = await Ticket.findOne({ TicketID: '2' }, { 'MembersID': { $slice: 1 } });
const firstMemberId = ticketDoc?.MembersID[0];

// find搭配投影
const ticketDocs = await Ticket.find({ TicketID: '2' }, { 'MembersID': { $slice: 1 } });
const firstMemberId = ticketDocs[0]?.MembersID[0];

内容的提问来源于stack exchange，提问作者Sebitas Aldas