I have this model:

const NeighborSchema = new Schema({
  friends: [
    {
      type: Schema.Types.ObjectId,
      ref: "users",
    },
  ],
  date: {
    type: Date,
    default: Date.now,
  },
});

module.exports = Neighbor = mongoose.model("neighbor", NeighborSchema);

I am trying to see if a friend exists in friends of all neighbors:

const mongoose = require("mongoose");
const ObjectId = mongoose.Types.ObjectId;
const testIncludes = async () => {
  let neighbors = await Neighbor.find();
  let friends_ids = [];

  neighbors.map((neighbor) => {
    const { friends } = neighbor;
    friends_ids = [...friends_ids, ...friends];
  });

  // Returns false for this
  const element_to_search = ObjectId("60dcbb29118ea36a4f3ce229");
  // Returns false for this
  // const element_to_search = "60dcbb29118ea36a4f3ce229";
  let is_element_found = friends_ids.includes(element_to_search);
};
// Returns false in both cases
testIncludes();

Even though, element_to_search was taken directly from list of returned friends_ids array, when I try to search it using include, it returns false for some reason, whether I search it as a String or as an ObjectId.

Any idea what's going on?

CodePudding user response：

Array.prototype.includes compares each element against the sample until it finds a match. Objects are considered equal only if they reference the same instance of the class. When you call a constructor const element_to_search = ObjectId("60dcbb29118ea36a4f3ce229"); it creates a new instance which has never been in the array, even if its value is the same.

You need to compare scalars. Strings for example:

friends_ids.map(f => f.toString()).includes("60dcbb29118ea36a4f3ce229");

or cast it strings when you build up the friends_ids at the first place to avoid the extra loop over the array.