在填充用户时遇到问题。 案例：
var User = new mongoose.Schema({
name: {
type: String,
lowercase: true,
unique: true
},
portfolio:[
{
name: String,
formatType: { type: mongoose.Schema.Types.ObjectId, ref: 'FormatType' },
}
]
});
这是我的Mongoose命令：
User.findById(req.payload.id)
.populate({
path:'portfolio',
populate:{
path: 'formatType',
model: 'FormatType'
}
})
.then(user => { ...
所以我们这里有一个模型 - 一个Obect内部 - 一个数组内部 - 在一个实体内部。
无法在线找到答案，非常感谢〜！
答案 0 :(得分：2)
您在这里基本上错过的是您想要populate()字段的“路径”，实际上是'portfolio.formatType'，而不仅仅是您输入的'portfolio'。由于这个错误和结构，你可能会有一些普遍的误解。
基本修正只需要正确的路径，并且您不需要model参数，因为这已经隐含在模式中：
User.findById(req.params.id).populate('portfolio.formatType');
这里的下一个一般观点是populate()本身有些“老帽子”，而且实际上并不是大多数新用户认为的那种“神奇”的东西。要清楚populate()是 NOT A JOIN ，它正在做的就是对服务器执行另一个查询以返回“相关”项，然后将该内容合并到返回的文档中来自上一个查询。
如果您正在寻找“加入”，那么您可能真的想要“嵌入”，如前所述。这实际上是处理“关系”的“MongoDB方式”，但是将所有“相关”数据保存在一个文档中。数据在不同集合中的“连接”的另一种方法是通过现代版本中的$lookup运算符。
由于您的“混合”内容数组形式，这会变得更复杂，但通常可以表示为：
// Aggregation pipeline don't "autocast" from schema
const { Types: { ObjectId } } = require("mongoose");
User.aggregate([
{ "$match": { _id: ObjectId(req.params.id) } },
{ "$lookup": {
"from": FormatType.collection.name,
"localField": "portfolio.formatType",
"foreignField": "_id",
"as": "formats"
}},
{ "$project": {
"name": 1,
"portfolio": {
"$map": {
"input": "$portfolio",
"in": {
"name": "$$this.name",
"formatType": {
"$arrayElemAt": [
"$formats",
{ "$indexOfArray": [ "$formats._id", "$$this.formatType" ] }
]
}
}
}
}
}}
]);
或者从MongoDB 3.6开始以更具表现力的$lookup形式：
User.aggregate([
{ "$match": { _id: ObjectId(req.params.id) } },
{ "$lookup": {
"from": FormatType.collection.name,
"let": { "portfolio": "$portfolio" },
"as": "portfolio",
"pipeline": [
{ "$match": {
"$expr": {
"$in": [ "$_id", "$$portfolio.formatType" ]
}
}},
{ "$project": {
"_id": {
"$arrayElemAt": [
"$$portfolio._id",
{ "$indexOfArray": [ "$$portfolio.formatType", "$_id" ] }
]
},
"name": {
"$arrayElemAt": [
"$$portfolio.name",
{ "$indexOfArray": [ "$$portfolio.formatType", "$_id" ] }
]
},
"formatType": "$$ROOT",
}}
]
}}
]);
这两种方法的工作方式略有不同，但两者基本上都与返回匹配的“相关”条目然后“重新映射”到现有数组内容以便与"name"属性合并“的概念一起工作”嵌入“阵列内部。这实际上是主要的复杂因素，否则这是一种相当直接的检索方法。
这与populate()在“客户端”上实际执行但在“服务器”上执行的过程几乎相同。因此，比较使用$indexOfArray运算符来查找匹配的ObjectId值的位置，然后通过$arrayElemAt操作从匹配的“index”返回数组中的属性。
唯一的区别是，在MongoDB 3.6兼容版本中，我们在“外部”内容 “之前进行”替换“” 将联接结果返回到父母。在之前的版本中，我们返回整个匹配的外部数组，然后使用$map“结合”两者以形成单个“合并”数组。
虽然这些最初可能看起来“更复杂”，但这里的最大优势是这些构成 “单一请求” 到 populate()发出和接收“多个”请求。这实际上节省了网络流量的大量开销，并大大增加了响应时间。
此外，这些都是“真正的联接”，所以你可以做更多的事情，这是“多个查询”无法实现的。例如，你可以在“加入”上“排序”结果并且仅返回最高结果，其中使用populate()需要引入“所有父母”才能查找返回结果的“孩子” 。对于孩子“加入”的“过滤”条件也是如此。
在Querying after populate in Mongoose上有关于一般限制的更多细节，以及你实际上甚至可以在必要时“自动化”生成这种“复杂”聚合管道语句的内容。
执行这些“连接”和理解引用模式的另一个常见问题是人们经常在存储引用的位置和时间以及它们如何工作时得到错误的概念。因此，以下列表用于说明此类数据的存储和检索。
在旧版NodeJS版本的原生Promises实现中：
const { Schema } = mongoose = require('mongoose');
const uri = 'mongodb://localhost/usertest';
mongoose.Promise = global.Promise;
mongoose.set('debug',true);
const formatTypeSchema = new Schema({
name: String
});
const portfolioSchema = new Schema({
name: String,
formatType: { type: Schema.Types.ObjectId, ref: 'FormatType' }
});
const userSchema = new Schema({
name: String,
portfolio: [portfolioSchema]
});
const FormatType = mongoose.model('FormatType', formatTypeSchema);
const User = mongoose.model('User', userSchema);
const log = data => console.log(JSON.stringify(data, undefined, 2));
(function() {
mongoose.connect(uri).then(conn => {
let db = conn.connections[0].db;
return db.command({ buildInfo: 1 }).then(({ version }) => {
version = parseFloat(version.match(new RegExp(/(?:(?!-).)*/))[0]);
return Promise.all(Object.entries(conn.models).map(([k,m]) => m.remove()))
.then(() => FormatType.insertMany(
[ 'A', 'B', 'C' ].map(name => ({ name }))
)
.then(([A, B, C]) => User.insertMany(
[
{
name: 'User 1',
portfolio: [
{ name: 'Port A', formatType: A },
{ name: 'Port B', formatType: B }
]
},
{
name: 'User 2',
portfolio: [
{ name: 'Port C', formatType: C }
]
}
]
))
.then(() => User.find())
.then(users => log({ users }))
.then(() => User.findOne({ name: 'User 1' })
.populate('portfolio.formatType')
)
.then(user1 => log({ user1 }))
.then(() => User.aggregate([
{ "$match": { "name": "User 2" } },
{ "$lookup": {
"from": FormatType.collection.name,
"localField": "portfolio.formatType",
"foreignField": "_id",
"as": "formats"
}},
{ "$project": {
"name": 1,
"portfolio": {
"$map": {
"input": "$portfolio",
"in": {
"name": "$$this.name",
"formatType": {
"$arrayElemAt": [
"$formats",
{ "$indexOfArray": [ "$formats._id", "$$this.formatType" ] }
]
}
}
}
}
}}
]))
.then(user2 => log({ user2 }))
.then(() =>
( version >= 3.6 ) ?
User.aggregate([
{ "$lookup": {
"from": FormatType.collection.name,
"let": { "portfolio": "$portfolio" },
"as": "portfolio",
"pipeline": [
{ "$match": {
"$expr": {
"$in": [ "$_id", "$$portfolio.formatType" ]
}
}},
{ "$project": {
"_id": {
"$arrayElemAt": [
"$$portfolio._id",
{ "$indexOfArray": [ "$$portfolio.formatType", "$_id" ] }
]
},
"name": {
"$arrayElemAt": [
"$$portfolio.name",
{ "$indexOfArray": [ "$$portfolio.formatType", "$_id" ] }
]
},
"formatType": "$$ROOT",
}}
]
}}
]).then(users => log({ users })) : ''
);
})
.catch(e => console.error(e))
.then(() => mongoose.disconnect());
})()
使用async/await语法获取更新的NodeJS版本，包括当前的LTS v.8.x系列：
const { Schema } = mongoose = require('mongoose');
const uri = 'mongodb://localhost/usertest';
mongoose.Promise = global.Promise;
mongoose.set('debug',true);
const formatTypeSchema = new Schema({
name: String
});
const portfolioSchema = new Schema({
name: String,
formatType: { type: Schema.Types.ObjectId, ref: 'FormatType' }
});
const userSchema = new Schema({
name: String,
portfolio: [portfolioSchema]
});
const FormatType = mongoose.model('FormatType', formatTypeSchema);
const User = mongoose.model('User', userSchema);
const log = data => console.log(JSON.stringify(data, undefined, 2));
(async function() {
try {
const conn = await mongoose.connect(uri);
let db = conn.connections[0].db;
let { version } = await db.command({ buildInfo: 1 });
version = parseFloat(version.match(new RegExp(/(?:(?!-).)*/))[0]);
log(version);
// Clean data
await Promise.all(Object.entries(conn.models).map(([k,m]) => m.remove()));
// Insert some things
let [ A, B, C ] = await FormatType.insertMany(
[ 'A', 'B', 'C' ].map(name => ({ name }))
);
await User.insertMany(
[
{
name: 'User 1',
portfolio: [
{ name: 'Port A', formatType: A },
{ name: 'Port B', formatType: B }
]
},
{
name: 'User 2',
portfolio: [
{ name: 'Port C', formatType: C }
]
}
]
);
// Show plain users
let users = await User.find();
log({ users });
// Get user with populate
let user1 = await User.findOne({ name: 'User 1' })
.populate('portfolio.formatType');
log({ user1 });
// Get user with $lookup
let user2 = await User.aggregate([
{ "$match": { "name": "User 2" } },
{ "$lookup": {
"from": FormatType.collection.name,
"localField": "portfolio.formatType",
"foreignField": "_id",
"as": "formats"
}},
{ "$project": {
"name": 1,
"portfolio": {
"$map": {
"input": "$portfolio",
"in": {
"name": "$$this.name",
"formatType": {
"$arrayElemAt": [
"$formats",
{ "$indexOfArray": [ "$formats._id", "$$this.formatType" ] }
]
}
}
}
}
}}
]);
log({ user2 });
// Expressive $lookup
if ( version >= 3.6 ) {
let users = await User.aggregate([
{ "$lookup": {
"from": FormatType.collection.name,
"let": { "portfolio": "$portfolio" },
"as": "portfolio",
"pipeline": [
{ "$match": {
"$expr": {
"$in": [ "$_id", "$$portfolio.formatType" ]
}
}},
{ "$project": {
"_id": {
"$arrayElemAt": [
"$$portfolio._id",
{ "$indexOfArray": [ "$$portfolio.formatType", "$_id" ] }
]
},
"name": {
"$arrayElemAt": [
"$$portfolio.name",
{ "$indexOfArray": [ "$$portfolio.formatType", "$_id" ] }
]
},
"formatType": "$$ROOT",
}}
]
}}
]);
log({ users })
}
mongoose.disconnect();
} catch(e) {
console.log(e)
} finally {
process.exit()
}
})()
后一个列表如果在每个阶段上进行评论以解释这些部分，您至少可以通过比较来看两种语法形式如何相互关联。
请注意，“表达式”$lookup示例仅在连接的MongoDB服务器实际支持语法的地方运行。
对于那些无法自己运行代码的人来说，“输出”：
Mongoose: formattypes.remove({}, {})
Mongoose: users.remove({}, {})
Mongoose: formattypes.insertMany([ { _id: 5b1601d8be9bf225554783f5, name: 'A', __v: 0 }, { _id: 5b1601d8be9bf225554783f6, name: 'B', __v: 0 }, { _id: 5b1601d8be9bf225554783f7, name: 'C', __v: 0 } ], {})
Mongoose: users.insertMany([ { _id: 5b1601d8be9bf225554783f8, name: 'User 1', portfolio: [ { _id: 5b1601d8be9bf225554783fa, name: 'Port A', formatType: 5b1601d8be9bf225554783f5 }, { _id: 5b1601d8be9bf225554783f9, name: 'Port B', formatType: 5b1601d8be9bf225554783f6 } ], __v: 0 }, { _id: 5b1601d8be9bf225554783fb, name: 'User 2', portfolio: [ { _id: 5b1601d8be9bf225554783fc, name: 'Port C', formatType: 5b1601d8be9bf225554783f7 } ], __v: 0 } ], {})
Mongoose: users.find({}, { fields: {} })
{
"users": [
{
"_id": "5b1601d8be9bf225554783f8",
"name": "User 1",
"portfolio": [
{
"_id": "5b1601d8be9bf225554783fa",
"name": "Port A",
"formatType": "5b1601d8be9bf225554783f5"
},
{
"_id": "5b1601d8be9bf225554783f9",
"name": "Port B",
"formatType": "5b1601d8be9bf225554783f6"
}
],
"__v": 0
},
{
"_id": "5b1601d8be9bf225554783fb",
"name": "User 2",
"portfolio": [
{
"_id": "5b1601d8be9bf225554783fc",
"name": "Port C",
"formatType": "5b1601d8be9bf225554783f7"
}
],
"__v": 0
}
]
}
Mongoose: users.findOne({ name: 'User 1' }, { fields: {} })
Mongoose: formattypes.find({ _id: { '$in': [ ObjectId("5b1601d8be9bf225554783f5"), ObjectId("5b1601d8be9bf225554783f6") ] } }, { fields: {} })
{
"user1": {
"_id": "5b1601d8be9bf225554783f8",
"name": "User 1",
"portfolio": [
{
"_id": "5b1601d8be9bf225554783fa",
"name": "Port A",
"formatType": {
"_id": "5b1601d8be9bf225554783f5",
"name": "A",
"__v": 0
}
},
{
"_id": "5b1601d8be9bf225554783f9",
"name": "Port B",
"formatType": {
"_id": "5b1601d8be9bf225554783f6",
"name": "B",
"__v": 0
}
}
],
"__v": 0
}
}
Mongoose: users.aggregate([ { '$match': { name: 'User 2' } }, { '$lookup': { from: 'formattypes', localField: 'portfolio.formatType', foreignField: '_id', as: 'formats' } }, { '$project': { name: 1, portfolio: { '$map': { input: '$portfolio', in: { name: '$$this.name', formatType: { '$arrayElemAt': [ '$formats', { '$indexOfArray': [ '$formats._id', '$$this.formatType' ] } ] } } } } } } ], {})
{
"user2": [
{
"_id": "5b1601d8be9bf225554783fb",
"name": "User 2",
"portfolio": [
{
"name": "Port C",
"formatType": {
"_id": "5b1601d8be9bf225554783f7",
"name": "C",
"__v": 0
}
}
]
}
]
}
Mongoose: users.aggregate([ { '$lookup': { from: 'formattypes', let: { portfolio: '$portfolio' }, as: 'portfolio', pipeline: [ { '$match': { '$expr': { '$in': [ '$_id', '$$portfolio.formatType' ] } } }, { '$project': { _id: { '$arrayElemAt': [ '$$portfolio._id', { '$indexOfArray': [ '$$portfolio.formatType', '$_id' ] } ] }, name: { '$arrayElemAt': [ '$$portfolio.name', { '$indexOfArray': [ '$$portfolio.formatType', '$_id' ] } ] }, formatType: '$$ROOT' } } ] } } ], {})
{
"users": [
{
"_id": "5b1601d8be9bf225554783f8",
"name": "User 1",
"portfolio": [
{
"_id": "5b1601d8be9bf225554783fa",
"name": "Port A",
"formatType": {
"_id": "5b1601d8be9bf225554783f5",
"name": "A",
"__v": 0
}
},
{
"_id": "5b1601d8be9bf225554783f9",
"name": "Port B",
"formatType": {
"_id": "5b1601d8be9bf225554783f6",
"name": "B",
"__v": 0
}
}
],
"__v": 0
},
{
"_id": "5b1601d8be9bf225554783fb",
"name": "User 2",
"portfolio": [
{
"_id": "5b1601d8be9bf225554783fc",
"name": "Port C",
"formatType": {
"_id": "5b1601d8be9bf225554783f7",
"name": "C",
"__v": 0
}
}
],
"__v": 0
}
]
}