How to loop through mongodb subdocument array find the matching elements and update the element fields with new values at once - mongodb

Question

For example, if a purchase order has line items like this:
and user from the client side send us line items to be updated in an array called lineItemsToUpdate and has a format like this:
[
{ unitCost: 342,
totalQuantity: 13,
acceptedQuantity: 6,
rejectedQuantity: 18,
title: 'Unbranded Concrete Pizza',
description: 'Soft',
variant: 5f2d5eb0195026e6dd549ef0 },
{ unitCost: 189,
totalQuantity: 95,
acceptedQuantity: 49,
rejectedQuantity: 16,
title: 'Handcrafted Rubber Cheese',
description: 'Assurance',
variant: 5f2d5eaf195026e6dd549b7d },
{ unitCost: 267,
totalQuantity: 18,
acceptedQuantity: 93,
rejectedQuantity: 11,
title: 'Incredible Soft Car',
description: 'solution-oriented',
variant: 5f2d5eb0195026e6dd549d3d },
]
here in the lineItemsToUpdate array, it's possible that the value of each element has been changed by the client and I want to update all the matching element by variant field in my sub-document if I describe it in the format of a user story:
update all lineItems "fields" according to lineItemsToUpdate array where the lineItemsToUpdate.[elem].variant === linitem.[elem].variant using $set, if possible $each and arrayFilters operators
I read some example through the mongodb documentation like this one:
db.students2.update(
{ },
{ $set: { "grades.$[elem].mean" : 100 } },
{
multi: true,
arrayFilters: [ { "elem.grade": { $gte: 85 } } ]
}
)
but the problem in here { $set: { "grades.$[elem].mean" : 100 } } is that the 100 value is constant and I want this part dynamic as I described in above.

Answer 1

Following is JS function you have to take help of.
function(c1,arr2){
var arr1 = c1.next().lineItems;
for(i=0;i<arr1.length;i++){
for(j=0;j<arr2.length;j++){
if(arr1[i].variant===arr2[j].variant){
db.purchaseOrder.update(
{ },
{ $set: { "lineItems.$[elem].unitCost" : arr2[j].unitCost,"lineItems.$[elem].totalQuantity" : arr2[j].totalQuantity } .....},
{ multi: true,
arrayFilters: [ { "elem.variant": { $eq: arr2[j].variant } } ]
}
)
}
}
}
}
Explanation
We have to pass 2 parameters: i) Mongo cursor and ii) An array.
Cursor is the collection to be updated. For your case, it is
Purchase Order. Array is lineItemsToUpdate array here.
Next we take 2 for loops to match variant field between cursor and
array.
If there is a match, we update the Purchase Order using update
command and $set operator.
Execution
Go to your Mongo Shell. Ensure the current database has Purchase
Order collection.
Define modifyItems function as below.
var modifyItems=function(c1,arr2){
var arr1 = c1.next().lineItems;
for(i=0;i<arr1.length;i++){
for(j=0;j<arr2.length;j++){
if(arr1[i].variant===arr2[j].variant){
db.purchaseOrder.update(
{ },
{ $set: { "lineItems.$[elem].unitCost" : arr2[j].unitCost,"lineItems.$[elem].totalQuantity" : arr2[j].totalQuantity }... },
{ multi: true,
arrayFilters: [ { "elem.variant": { $eq: arr2[j].variant } } ]
}
)
}
}
}
}
Define a variable arr which contains lineItemsToUpdate.
var arr=[
{ unitCost: 342,
totalQuantity: 13,
acceptedQuantity: 6,
rejectedQuantity: 18,
title: 'Unbranded Concrete Pizza',
description: 'Soft',
variant: 5f2d5eb0195026e6dd549ef0 },
{ unitCost: 189,
totalQuantity: 95,
acceptedQuantity: 49,
rejectedQuantity: 16,
title: 'Handcrafted Rubber Cheese',
description: 'Assurance',
variant: 5f2d5eaf195026e6dd549b7d },
{ unitCost: 267,
totalQuantity: 18,
acceptedQuantity: 93,
rejectedQuantity: 11,
title: 'Incredible Soft Car',
description: 'solution-oriented',
variant: 5f2d5eb0195026e6dd549d3d }
]
Now execute the JS function.
modifyItems(db.purchaseOrder.find({},{"lineItems":1,"_id":0}),arr);
If there is no error, your Purchase Order line items will be now updated with the array values in one single shot.