猫鼬如何进行多次更新

Question

I'm having a tough time coming up with a solution to update multiple documents with different values.

I have an app that makes sales for every sold item I want to reduce the quantity in my database by one.

var soldItems = 
[

    {
        "_id": "1"
        "name": "Foo",
        "price": 1.09
    },
    {
        "_id": "2",
        "name": "Bar",
        "price": 2.00
    }

]

var ids = [];

soldItems.forEach(function(item){

   ids.push(item._id);

});

I'm collecting all the ids in my soldItems array of objects.

Now I want to know how many items quantity I have in the database and then reduce the number quantity by one.

ModelItem.find({_id: {$in: ids}}, function(err, docs){
    if(err) throw err;

    docs.forEach(function(doc){

        soldItems.forEach(function(item){

            if(doc._id === item._id){
                doc.quantity += -1;
            }

        });            

    });

    Item.update({_id: {$in: ids}}, {$set: docs }, function(err){
        if(err) throw err;


    });

});

Obviously this is wrong because $set is passing in array instead of an object.

I want to know how can I reduce the quantity by one for each item in my database, but I the same time I don't want to go below 0 items in the database.

I'm sure im looking at this from the wrong angle.

Thanks.

Answer 1

Use the $inc operator instead, and the multi options:

Item.update({_id: {$in: ids}, quantity: {$gt: 0}}, // selection
            {$inc: {quantity: -1}}, // modifications
            {multi: true}); //options