how do I increment field in array of objects after finding it (using findOne()) and before saving it?

Question

I want to update an object inside an array of schemas without having to do two requests to the database. I currently am incrementing the field using findOneAndUpdate() if the object already exists and it works fine. but in case the object does not exist then I am having to make another request using update() to push the new object and make it available for later increments.

I want to be able to do only one request (e.g. findOne()) to get the user and then increment the field only if object exists in the array and if not I would like to push the new object instead. then save the document. this way I am only making one read/request from the database instead of two.

this is the function now:

  async addItemToCart(body, userId) {
const itemInDb = await Model.findOneAndUpdate(
  {
    _id: userId,
    'cart.productId': body.productId,
  },
  { $inc: { 'cart.$.count': 1 } }
);
if (itemInDb) return true;

const updated = await Model.update(
  { _id: userId },
  { $push: { cart: body } }
);
if (updated.ok !== 1)
  return createError(500, 'something went wrong in userService');
return true;
}

what I would like to do is:

  async addItemToCart(body, userId) {
const itemInDb = await Model.findOne(
  {
    _id: userId,
    'cart.productId': body.productId,
  }
);
if (itemInDb) {
  /**
   * 
   * increment cart in itemInDb then do itemInDb.save()  <<------------
   */
} else {
  /**
   * push product to itemInDb then save
   */
}

Thank you!

IftekharDani · Accepted Answer · 2018-10-12 06:22:26Z

2

You can try findOneAndUpdate with upsert.

upsert: true then create data if not exists in DB.

Model.findOneAndUpdate(
  {
    _id: userId,
    'cart.productId': body.productId,
  },
  { $inc: { 'cart.$.count': 1 } },
 {
     upsert: true,
   }
)

Use $set and $inc in one query.

try {
  db.scores.findOneAndUpdate(
    {
      _id: userId,
      'cart.productId': body.productId,
    },
     { $set: { "cart.$.productName" : "A.B.C", "cart.$.productPrice" : 5}, $inc : { "cart.$.count" : 1 } },
     { upsert:true, returnNewDocument : true }
  );
  }
  catch (e){
     //error
  }

reference Link : here

edited Oct 12, 2018 at 6:22

answered Oct 12, 2018 at 5:16

IftekharDani

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2 Comments

tito.300 Over a year ago

The product in cart array has more fields than “count”, how do I add those if they object doesn’t exist?

tito.300 Over a year ago

it did not work because what I'm dealing with is an array of embedded sub documents. turns out to do it I would have to introduce a lot more complexity. check this answer: stackoverflow.com/a/49204544/9111239 . thank you for your effort!

Surjeet Bhadauriya · Accepted Answer · 2018-10-12 05:28:20Z

You can use upsert.

upsert is defined as an operation that creates a new document when no document matches the query criteria and if matches then it updates the document. It is an option for the update command. If you execute a command like below it works as an update, if there is a document matching query, or as an insert with a document described by the update as an argument.

Example: I am just giving a simple example. You have to change it according to your requirement.

db.people.update(
   { name: "Andy" },
   {
      name: "Andy",
      rating: 1,
      score: 1
   },
   { upsert: true }
)

So in the above example, if the people with name Andy is found then the update operation will be performed. If not then it will create a new document.

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