如何修复我的 mongoose/mongodb 搜索功能的“未定义”返回答案

【问题标题】：How to fix the "undefined" return from my mongoose/mongodb search function如何修复我的 mongoose/mongodb 搜索功能的“未定义”返回
【发布时间】：2019-05-28 13:12:46
【问题描述】：

我正在尝试从 mongodb 获取结果，然后将其传递给 const，但是得到“未定义”的返回值我哪里出错了？

我确保代码在没有返回的情况下工作并打印到控制台，并确保数据集存在于我的 mongodb 中。

const mongoose = require('mongoose');

function search(query) {
  const search = db.collection('spells').find({
    "name": query
  }).then(function(cursor) {
    cursor.forEach(function(spell) {
      console.log(spell);
      return spell;
    });
  });
}

mongoose.connect('mongodb://localhost/dnd', {
  useNewUrlParser: true
});

const db = mongoose.connection;

db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function() {
  console.log("Connected to DB" + "\n");

});

console.log(search("Blight"));

当上面运行时，我在命令行上得到以下输出

未定义

连接到数据库

然后它打印以下是MongoDB中的数据

{ _id: 5ced1ce8aa89b60a7c2e34de,
  name: 'Blight',
  level: 4,
  school: 'N',
  time: [ { number: 1, unit: 'action' } ],
  range: { type: 'point', distance: { type: 'feet', amount: 30 } },
  components: { v: true, s: true },
  duration: [ { type: 'instant' } ],
  classes:
   { fromClassList: [ [Object], [Object], [Object], [Object] ],
     fromSubclass:
      [ [Object], [Object], [Object], [Object], [Object], [Object] ] },
  source: 'PHB',
  entries:
   [ 'Necromantic energy washes over a creature of your choice that you can see within range, draining moisture and vitality from it. The target must make a Constitution saving throw. The target takes {@dice 8d8} necrotic damage on a failed save, or half as much damage on a succ
essful one. This spell has no effect on undead or constructs.',
     'If you target a plant creature or a magical plant, it makes the saving throw with disadvantage, and the spell deals maximum damage to it.',
     'If you target a nonmagical plant that isn\'t a creature, such as a tree or shrub, it doesn\'t make a saving throw, it simply withers and dies.' ],
  entriesHigherLevel:
   [ { type: 'entries', name: 'At Higher Levels', entries: [Array] } ],
  page: 219,
  damageInflict: [ 'necrotic' ],
  savingThrow: [ 'constitution' ] }

我希望能够通过返回而不是在函数内部获取数据。

【问题讨论】：

标签： node.js mongodb mongoose

【解决方案1】：

您当前正在将数据返回给 Promise，但您的函数没有返回任何内容，您可以返回数组对象并稍后处理结果

async function search(query) {
  try {
    const search = await db.collection('spells').find({
      "name": query
    }).toArray();
    return search;
  } catch(err) {
    throw new Error(err);
  }
}

【讨论】：

【解决方案2】：

const mongoose = require('mongoose');

function search(query) {
   return db.collection('spells').find({
    "name": query
  })
}

mongoose.connect('mongodb://localhost/dnd', {
  useNewUrlParser: true
});

const db = mongoose.connection;

db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function() {
  console.log("Connected to DB" + "\n");       
  search("Blight").then(console.log);
});

【讨论】：

【解决方案3】：

在 freenode/#Node.js 中从 avu 获得一些建议后，我研究了 Promise 并提出了这个问题。

const mongoose = require('mongoose');

function search(query) {
  return new Promise(function(resolve) {
      const findspell = db.collection('spells').find({
        "name": query
      }).then(function(cursor) {
        cursor.forEach(function(spell) {
          resolve(spell)
        });
      });
    });
  }

  mongoose.connect('mongodb://localhost/dnd', {
    useNewUrlParser: true
  });

  const db = mongoose.connection;

  db.on('error', console.error.bind(console, 'connection error:'));
  db.once('open', function() {
    console.log("Connected to DB" + "\n");

  });

  search("Blight").then(console.log(response)});

【讨论】：