Removing an element from array in mongodb

问题

I want to remove a specific element from array stored in mongodb document. I am using this:

 model.registerCompany.findOneAndUpdate({companyKey:"a key"},
    {$pop:{onlineEmployees:"John"}},
    function(err,doc){
    if(!err)
        console.log("Online list modified: ",doc);
    else
        console.log("Online list modified error :",err);
});

But I am not sure if the $pop removes the specific element "John" from array(onlineEmployees) or just pop out the last element from it.

Am i doing it right or there is another way to do it.?

I think i got the answer .. $pull is used for this purpose as explained here in the link: http://docs.mongodb.org/manual/reference/operator/pull/#_S_pull

回答1:

The $pop operator will remove first or last element of the array, which may not necessarily be the right one.

If you want a specific element, you can $pull the item with defined criteria:

   model.registerCompany.findOneAndUpdate({companyKey:"a key"},
    {$pull:{onlineEmployees:"John"}},

You have to make sure the value in the array is unique, for $pull removes every element matching the name 'John'.

If identical values exist in the array, you need to use $unset and $ positional operator to set the target element value to null(unfortunately $unset won't remove elements) and then use $pull to remove the element with null value. To do that, you have to make sure valid value can not be null. In that case, the code could be like:

model.registerCompany.findOneAndUpdate({companyKey:"a key", onlineEmployees:"John"},{ $unset: { "onlineEmployees.$" : '' } } ) 
model.registerCompany.findOneAndUpdate({companyKey:"a key"},{ $pull: { "onlineEmployees" : null } } ) 

来源：https://stackoverflow.com/questions/14472858/removing-an-element-from-array-in-mongodb