如何在一个请求中对 mongo 进行多个查询

Question

Let say I have a collection of Person{email: 'actual email', ..other data} and want to query if Person exists with given email and retrieve it data if so or get a null if not.

If i want to do that once than no problem just do a query, through mongoose using Person.findOne() or whatever.
But what if I have to do a check for 25-100 given emails? Of course I can just send a tons of requests to mongodb and retrieve the data but it seems a vast of network.

Is there a good and perfomant way to query a mongodb with multiple clauses in single batch like findBatch([{email: 'email1'}, {email: 'email2'}...{email: 'emailN'} ]) and got as result [document1,null,document3,null, documentN] where null is for not matched find criterias?

Currently I see only one option:

1. Huge find with single {email: $in: [] } query and that do a matching through the searching on the server side in application logic. Cons: quite cumbersome and error prone if you have more than one search criteria.

Is there any better ways to implement such thing?

Answer 1

Try this:

• Replace the arrayOfEmails with your query array
• Replace emailField with the actual name in your db documents

db.collName.aggregate([
    {
        "$match" : {
            "emailField" : {
                "$in" : arrayOfEmails
            }
        }
    },
    {
        "$group" : {
            "_id" : null,
            "docs" : {
                "$push" : {
                    "$cond" : [
                        {
                            "$in" : [
                                arrayOfEmails,
                                [
                                    "$emailField"
                                ]
                            ]
                        },
                        "$$ROOT",
                        null
                    ]
                }
            }
        }
    }
])