MongoDB使用$elemMatch匹配数组多元素查询失败问题咨询

Absolutely, MongoDB does support this kind of query using $elemMatch—your approach is actually on the right track. Let's break down why you might not be seeing expected results, confirm the correct execution, and cover some edge cases.

First: Your Query Logic Is Correct #

Running your exact query against the sample dataset you provided does return the document, because the arrivals array contains an element that matches both conditions:

• number: "KL 1451"
• movement.scheduledTimeLocal includes "2020-05-23"

Here's how to verify this step-by-step:

1. Insert the Sample Data #

First, add your test document to a collection (replace flights with your actual collection name):

db.flights.insertOne({
  "departures": [
    {
      "movement": {
        "airport": { "icao": "EHAM", "iata": "AMS", "name": "Amsterdam" },
        "scheduledTimeLocal": "2020-05-23 12:25+01:00",
        "scheduledTimeUtc": "2020-05-23 11:25Z",
        "quality": [ "Basic" ]
      },
      "number": "KL 1446",
      "status": "CanceledUncertain",
      "codeshareStatus": "IsOperator",
      "isCargo": false,
      "aircraft": { "model": "Embraer 190" },
      "airline": { "name": "KLM" }
    },
    {
      "movement": {
        "airport": { "icao": "EGLL", "iata": "LHR", "name": "London" },
        "scheduledTimeLocal": "2020-05-23 14:50+01:00",
        "scheduledTimeUtc": "2020-05-23 13:50Z",
        "quality": [ "Basic" ]
      },
      "number": "BA 1309",
      "status": "Unknown",
      "codeshareStatus": "IsOperator",
      "isCargo": false,
      "aircraft": { "model": "Airbus A319" },
      "airline": { "name": "British Airways" }
    }
  ],
  "arrivals": [
    {
      "movement": {
        "airport": { "icao": "LFPG", "iata": "CDG", "name": "Paris" },
        "scheduledTimeLocal": "2020-05-23 21:10+01:00",
        "scheduledTimeUtc": "2020-05-23 20:10Z",
        "quality": [ "Basic" ]
      },
      "number": "AF 1472",
      "status": "Unknown",
      "codeshareStatus": "Unknown",
      "isCargo": false,
      "aircraft": { "model": "Embraer 170" },
      "airline": { "name": "Air France" }
    },
    {
      "movement": {
        "airport": { "icao": "EHAM", "iata": "AMS", "name": "Amsterdam" },
        "scheduledTimeLocal": "2020-05-23 22:15+01:00",
        "scheduledTimeUtc": "2020-05-23 21:15Z",
        "quality": [ "Basic" ]
      },
      "number": "KL 1451",
      "status": "CanceledUncertain",
      "codeshareStatus": "IsOperator",
      "isCargo": false,
      "aircraft": { "model": "Boeing 737-700" },
      "airline": { "name": "KLM" }
    }
  ]
})

2. Run Your Query #

Execute your original query (again, replace flights with your collection name):

db.flights.find({
  arrivals: {
    $elemMatch: {
      'number': 'KL 1451',
      'movement.scheduledTimeLocal': { $regex: /2020-05-23/ }
    }
  }
})

This will return the full document as expected, since the arrivals array has a matching element.

Why You Might Not Be Seeing Results #

If you're getting no hits, check these common issues:

• Wrong collection name: You wrote db.collection.find(...)—make sure collection is replaced with your actual collection's name (like flights, airport_data, etc.).
• Hidden whitespace in data: Double-check if the number field in your real data has extra spaces (e.g., "KL 1451" instead of "KL 1451"). Test with a regex for the number: 'number': { $regex: /^KL\s1451$/ }
• Regex edge cases: While your regex works for the sample data, if your real timestamps use different formatting, you might need to adjust it (e.g., $regex: "2020-05-23", $options: "i" for case insensitivity, though that's not needed here).
• Outdated MongoDB version: $elemMatch has been supported since MongoDB 2.2, so this is only an issue if you're using a very old version.

Bonus: Return Only Matching Array Elements #

If you don't want the entire document and just need the matching arrivals element(s):

• To return the first matching element (all MongoDB versions):

  db.flights.find(
    { arrivals: { $elemMatch: { 'number': 'KL 1451', 'movement.scheduledTimeLocal': { $regex: /2020-05-23/ } } } },
    { 'arrivals.$': 1 } // Projects only the first matching array element
  )
  

• To return all matching elements (MongoDB 3.2+):

  db.flights.aggregate([
    { $match: { arrivals: { $elemMatch: { 'number': 'KL 1451', 'movement.scheduledTimeLocal': { $regex: /2020-05-23/ } } } } },
    {
      $project: {
        arrivals: {
          $filter: {
            input: "$arrivals",
            cond: {
              $and: [
                { $eq: ["$$this.number", "KL 1451"] },
                { $regexMatch: { input: "$$this.movement.scheduledTimeLocal", regex: /2020-05-23/ } }
              ]
            }
          }
        }
      }
    }
  ])
  

内容的提问来源于stack exchange，提问作者Scotty