node.js 使用猫鼬检查集合中是否存在 ID
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Check if ID exists in a collection with mongoose
提问by Michael
For instance, I have a collection User:
例如，我有一个集合User：
var mongoose = require('mongoose');
var UserSchema = new mongoose.Schema({
email: String,
googleId: String,
facebookId: String,
displayName: String,
active: Boolean
});
module.exports = mongoose.model('User', UserSchema);
And then I have an ID:
然后我有一个ID：
var userID = "some-user-id"
What is the right way to just check if this id exists in the Usercollection. I don't need it to read the file or return it, I just need the trueor falsevalue.
仅检查User集合中是否存在此 id 的正确方法是什么。我不需要它来读取文件或返回它，我只需要trueorfalse值。
Here is one way to achieve it:
这是实现它的一种方法：
User.findOne({
_id: userID
}, function (err, existingUser) {
But is there faster and more efficient way?
但是有没有更快更有效的方法呢？
回答by Alex
Use countrather than findOne.
使用count而不是 findOne。
This will (under the hood) cause mongoose to use find: http://docs.mongodb.org/manual/reference/method/db.collection.count
这将（在幕后）导致猫鼬使用find：http: //docs.mongodb.org/manual/reference/method/db.collection.count
findOne()will read + return the document if it exists
On the other hand, find()just returns a cursor (or not) and only reads the data if you iterate over the cursor.
So in our case, we're not iterating over the cursor, merely counting the results returned.
findOne()将读取 + 返回文档（如果存在）另一方面，find()只返回一个游标（或不返回），并且只有在遍历游标时才读取数据。所以在我们的例子中，我们没有迭代游标，只是计算返回的结果。
User.count({_id: userID}, function (err, count){
if(count>0){
//document exists });
}
});
回答by Tom
You can now use User.exists()as of September 2019like so:
User.exists()从2019 年 9 月起，您现在可以像这样使用：
const doesUserExit = await User.exists({ _id: userID });
const doesUserExit = await User.exists({ _id: userID });
From the docs:
从文档：
Under the hood,
MyModel.exists({ answer: 42 })is equivalent toMyModel.findOne({ answer: 42 }).select({ _id: 1 }).lean().then(doc => !!doc)
在引擎盖下，
MyModel.exists({ answer: 42 })相当于MyModel.findOne({ answer: 42 }).select({ _id: 1 }).lean().then(doc => !!doc)
回答by Alisson
The accepted answer is fine for small collections.
接受的答案适用于小型收藏。
A faster way on larger collectionsis to simply use this:
一对大集合更快的方法是简单地使用：
const result = await User.findOne({ _id: userID }).select("_id").lean();
if (result) {
// user exists...
}
// or without "async/await":
User.findOne({ _id: userID }).select("_id").lean().then(result => {
if (result) {
// user exists...
}
});
It won't return all fields. I believe they are currently working on a new featureto support what you (and I) want.
它不会返回所有字段。我相信他们目前正在开发一项新功能来支持你（和我）想要的。
In the meantime you could create a plugin, very simple and reusable.
与此同时，您可以创建一个插件，非常简单且可重用。
Create an any.jsfile with this code:
any.js使用以下代码创建一个文件：
module.exports = function any(schema, options) {
schema.statics.any = async function (query) {
const result = await this.findOne(query).select("_id").lean();
return result ? true : false;
};
}
Then in your model you do this:
然后在你的模型中你这样做：
var mongoose = require('mongoose');
const any = require('./plugins/any'); // I'm assuming you created a "plugins" folder for it
var UserSchema = new mongoose.Schema({
email: String,
googleId: String,
facebookId: String,
displayName: String,
active: Boolean
});
UserSchema.plugin(any);
module.exports = mongoose.model('User', UserSchema);
...and use it like this:
...并像这样使用它：
const result = await User.any({ _id: userID });
if (result) {
// user exists...
}
// or without using "async/await":
User.any({ _id: userID }).then(result => {
if (result) {
// user exists...
}
});
回答by Hasan Sefa Ozalp
User.exists({ _id: userID }).then(exists => {
if (exists) {
res.redirect('/dashboard')
} else {
res.redirect('/login')
}
})
More info can be found at Mongoose docs.
更多信息可以在Mongoose 文档中找到。
