NodeJS / Mongoose：在forEach循环中推送值后数组变空

Question

I am using Mongoose Reference Schema and trying to get all entities of the current user, and pushing it to the array, but after forEach loop ends, the array is getting empty

let entityList = [];

Entity.find({})
      .populate('host')
      .exec( function(err, entities)
      {
            //Iterate through each entity, find if it belongs to current user
            //If it belongs, add to the list
            entities.forEach((entity)=>
            {
                  console.log(entity);
                  console.log(entity.host._id);
                  if(entity.host._id == req.params.id){
                        console.log("Found");
                        entityList.push(entity);
                        console.log(entityList);    //Printing the value
                  }
            });
      });
//Not being logged
entityList.forEach((i)=>{
      console.log(i);
});
console.log(entityList); //Empty array

EntitySchema:

const entitySchema = new Schema({
      username: String,
      userType: String,
      host: { 
            type: mongoose.Schema.Types.ObjectId,
            ref: 'User'
      }
});

const Entity = mongoose.model("Entity",entitySchema);

UserSchema:

const userSchema = new Schema({
      socialMediaID: String,
      username: String,
      thumbnail: String
});

const User = mongoose.model("User",userSchema);

Answer 1

The exec() function returns immediately. Your code continues with logging entityList . But at that time the list is still empty.

The callback, which fills entityList , is called sometimes later (asynchronously).