How to use count query in an array of object array using Nodejs , mongodb and express?

Question

I have 2 models one is called User and the other Item. An array of items is assigned to each User(each user has 5 items). Through each user's session, the user can classify the items to Qualified or Not Qualified or none of them. Here is the Models:

const ItemSchema = new Schema({
  title: {
    type: String,
  },
  classification: {
    type: String,
  }
});
//Create the User Schema
const UserSchema = new Schema({
  username: {
    type: String,
    required: true,
  },
  password: {
    type: String,
    required: true,
  },
  items: [ItemSchema],
});

UserSchema.pre("save", function (next) {
  this.items = [];
  this.items.push({
    title: "Item 1",
    classification: ""
  });
  this.items.push({
    title: "Item 2",
    classification: ""
  });
  this.items.push({
    title: "Item 3",
    classification: ""
  });
  next();
});
module.exports = User = mongoose.model("users", UserSchema);

As you can see the user's items has classification property which can be written "Qualified" or "Not Qualified" or "" in it. What I like to do is to count how many users classify Item 1 as "Qualified" and how many as "Not Qualified" & how many as "".So if 3 users classified Item 1 as "Qualified" and 2 users as "Not Qualified", I can say Item 1 is "Qualified".

Pawan Bishnoi · Accepted Answer · 2021-06-02 08:35:30Z

1

// count Qualified And Item One
const res = await User.count({items:{ $elemMatch: { title: "Item 1",classification:"Qualified"}}}});

const res = await User.count({items:{ $elemMatch: { title: "Item 1",classification:"Not Qualified"}}}});

const res = await User.count({items:{ $elemMatch: { title: "Item 1",classification:""}}}});

answered Jun 2, 2021 at 8:35

Pawan Bishnoi

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2 Comments

FFXX Over a year ago

thank you,it worked! But in case I would have 20 items.Is there any way to loop through all the items or I should do for all of them separately like above?

Pawan Bishnoi Over a year ago

Querying database in loop is not a good choice also aggregation for multiple stage can be complex, as a alternate way you can use below code const docs = await User.count().select({results:1}); const aggregate = {}; for(document of docs ){ if(!aggregate[document.item]){ aggregate[document.item] = {} } if(!aggregate[document.item][document.classification]){ aggregate[document.item][document.classification] = 0; } aggregate[document.item][document.classification] ++; } due to character limit i can't post full code in comment, handle classification empty case

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