MongoDB为什么要为该模式中不存在的字段创建索引？

Question

TL;DR: I am having trouble with my mongo database seemingly creating indexes for my boards collection from fields from my users collection which is causing E11000 errors when I try to create a new board.

I am building a kanban board (like Jira) and have board, task and user collections (entity relationship diagram : https://imgur.com/a/Nu6Eg91 ). All of the collections work fine following a .dropIndexes(). However, when I have been working with tasks via the UI on one board, when I try to create another board I get this E11000 error:

{ MongoError: insertDocument :: caused by :: 11000 E11000 duplicate key error index: kanban.boards.$username_1  dup key: { : null }
    at Function.create (/home/ubuntu/workspace/kanban v1.0/node_modules/mongodb-core/lib/error.js:43:12)
    at toError (/home/ubuntu/workspace/kanban v1.0/node_modules/mongodb/lib/utils.js:149:22)
    at coll.s.topology.insert (/home/ubuntu/workspace/kanban v1.0/node_modules/mongodb/lib/operations/collection_ops.js:859:39)
    at /home/ubuntu/workspace/kanban v1.0/node_modules/mongodb-core/lib/connection/pool.js:532:18
    at _combinedTickCallback (internal/process/next_tick.js:73:7)
    at process._tickCallback (internal/process/next_tick.js:104:9)
  driver: true,
  name: 'MongoError',
  index: 0,
  code: 11000,
  errmsg: 'insertDocument :: caused by :: 11000 E11000 duplicate key error index: kanban.boards.$username_1  dup key: { : null }' }

This appears to be because of a null value in the username field in the board schema but there is no such field in this model as can be seen below:

// Board Schema

// Config
var mongoose = require("mongoose"),
    passportLocalMongoose = require("passport-local-mongoose");


// Create Board Schema

var BoardSchema = new mongoose.Schema({
    user: {type: mongoose.Schema.Types.ObjectId, ref: "User", unique: true, sparse: true},
    todo: [{type: mongoose.Schema.Types.ObjectId, ref: "Task"}],
    inProgress: [{type: mongoose.Schema.Types.ObjectId, ref: "Task"}],
    testing: [{type: mongoose.Schema.Types.ObjectId, ref: "Task"}],
    completed: [{type: mongoose.Schema.Types.ObjectId, ref: "Task"}]
});


// Validation
BoardSchema.plugin(passportLocalMongoose);


// Export Model
module.exports = mongoose.model("Board", BoardSchema);

Here is an example board in the db:

{ "_id" : ObjectId("5c65767c8977670a2366ffe5"), 
"todo" : [ ObjectId("5c657a1e451bc80ac315ef35"), ObjectId("5c657a4a451bc80ac315ef37"), ObjectId("5c657a76451bc80ac315ef39") ], 
"inProgress" : [ ObjectId("5c6579e1451bc80ac315ef31"), ObjectId("5c657a03451bc80ac315ef33"), ObjectId("5c657a3a451bc80ac315ef36"), ObjectId("5c657a8a451bc80ac315ef3a") ], 
"testing" : [ ObjectId("5c657a9a451bc80ac315ef3b") ], 
"completed" : [ ObjectId("5c657a60451bc80ac315ef38"), ObjectId("5c65bb8f6f5b731aec27b4a7"), ObjectId("5c65bba06f5b731aec27b4a8"), ObjectId("5c657a11451bc80ac315ef34") ], 
"user" : ObjectId("5c65767b8977670a2366ffe4"), 
"__v" : 51 }

For some reason, I think a username index has been created by the database for the boards schema. The indexes for the boards collection are below:

[
        {
                "v" : 1,
                "key" : {
                        "_id" : 1
                },
                "name" : "_id_",
                "ns" : "kanban.boards"
        },
        {
                "v" : 1,
                "key" : {
                        "user" : 1
                },
                "name" : "user_1",
                "ns" : "kanban.boards",
                "background" : true
        },
        {
                "v" : 1,
                "unique" : true,
                "key" : {
                        "username" : 1
                },
                "name" : "username_1",
                "ns" : "kanban.boards",
                "background" : true
        }
]

For completeness, here is the user schema:

// User Schema

// Config

var mongoose = require("mongoose"),
    uniqueValidator = require("mongoose-unique-validator"),
    passportLocalMongoose = require("passport-local-mongoose");


// Create User Schema

var UserSchema = new mongoose.Schema({
    username: {type: String, required: true, unique: true},
    password: String
});


// Validation and Hash/Salt PW
UserSchema.plugin(uniqueValidator, {message: "A user is already registered with that {PATH}."});
UserSchema.plugin(passportLocalMongoose);


// Export Model
module.exports = mongoose.model("User", UserSchema);

The code causing the error is in the signup route, part of which is shown below:

// create new board for user
        var newBoard = {
            user: user._id,
            todo: [],
            inProgress: [],
            testing: [],
            review: [],
            completed: [],
        };


        Board.create(newBoard, function(err, board) {
            if(err) {
                console.log(err);
                req.flash("error", "Uh oh! Something went wrong.");
                return res.redirect("/");
            }

            // authenticate user
            passport.authenticate("local")(req, res, function() {
                req.flash("success", "Welcome to your Kanban board, " + user.username + ".");
                return res.redirect("/board");
            });

        });

I don't understand why this index is being created (or indeed if this is what is causing the E11000 errors but I'm pretty sure it is). Apologies for the spam of code, I am quite inexperienced with using mongo and so don't know what is relevant and what is not. I have built mongo databases with multiple collections before but not with a link collection as I have here so I can't work out what is going wrong. Please let me know if I have missed anything that is useful or important. Thanks.

Answer 1

I'm not 100% sure if this is the issue, but you should remove the unique: true and sparse: true from the BoardSchema.user parameter. Since you declare those in the UserSchema, you shouldn't also need them in the BoardSchema.

EDIT: You might also have to manually delete the index after completing this first step.

Answer 2

问题是我只将护照本地猫鼬插入到董事会架构中，而这只应位于用户架构中。