Mongo db conditional query

问题

being a newbie to mongo, stuck in a conditional query: I want to perform a search on the basis of 3 criteria, first name, last name and email id: below query works perfect when all the fields exist:

db.students.find( { $and: [ { first_name:  /^Abc$/i }, { last_name:         'Xyz'},{email_id:'gd@he'} ]})

the problem is when I don't give an email id , the query dosen't returns any result as it considers the email id to be null and searches for the combination 'Abc Firtis null', where as I want the below scenario to be fulfilled: I have a collection of students:

- FirstName: 1. ABC 2. ABC 3.ABC
- LastName:  1.XYZ 2. XY 3. XZ
- EmailID:   1.abc@xyz  2.Ab@xy 3.Ab@xz

if one enters only the first name in the search it should return all the 3 results if user enters first name and last name it should return first two results and if the user enters all three details it should return only 1 result.

Any leads would be highly appreciated.

回答1:

You seem to be talking about "input" data being different for the queries you want to issue and how to contruct the query to ignore fields as criteria for which you have no input.

This is all really about how the input is being collected as to how you handle it, but it all boils down to that you "conditionally build" the query ( which is just a data structure anyway ) rather than statically define a query and somehow ignore null or empty data.

So if you have seperate variables, then you test each value and build the query:

var firstName = "abc",
    lastName = "xy,
    email = null,
    query = {};

if (firstName) {
    query.firstName = new RegExp("^"+firstName,"i")
}

if (lastName) {
    query.lastName = new RegExp("^"+lastName,"i")
}

if (email) {
    query.email = new RegExp("^"+email,"i")
}

db.students.find(query)

This would build a query object that would end up like this based on the inputs:

{ "firstName": /^abc/i, "lastName": /^xy/i }

So since there is no value in email then the condition is not included. The end result is the condition not provided is not even queried for and then you get the relevant matches.

The same approach is basically simplified if you have some structured input to begin with:

var params = {
    firstName = "abc",
    lastName = "xy"
};

var query = {};

Object.keys(params).forEach(function(key) {
    if (params[key])
        query[key] = new RegExp("^"+key,"i");
});

db.students.find(query);

And it's the same thing, but since you have all parameter keys in one place then you can iterate them to build the query rather than test individually.

This is generally the case where you have input from something like a web request with parameters that come into req.params or even req.body depending on your method of input. So if you structure your code to accept input into a similar object ( or already have it ) then you use it to build your query.

Also note that all MongoDB query arguments are implicitly an "AND" condition by definition, so there is rarely any need to use $and unless you explicitly have multiple conditions to meet for the same document property. Even then there are generally better syntax alternates.

回答2:

No Need to give and you can simply try this

find( { first_name: { $regex: '/^Abc$/i' }, last_name:'Xyz',email_id:'gd@he'}

来源：https://stackoverflow.com/questions/32815970/mongo-db-conditional-query

标签

mongodb

mongodb-query