Mongoose: Guaranteeing that the array will never surpass a specific limit of items

Question

Mongoose: Guaranteeing that the array will never surpass a specific limit of items

Struggling to understand the proper syntax for a set operation in Mongoose. My schema is structured like this:

const userSchema = mongoose.Schema({
  instagram: {
    images: [{
      id: { type: String },
      media_type: { type: String },
      media_url: { type: String },
      timestamp: { type: Date }
    }]
  }
});

I need to regularly update this array with the most recent Instagram photos from the user:

User.findOneAndUpdate({ _id }, { $addToSet: { "instagram.images": { $each: arr } } });

How can I ensure that the array always contains the latest images, but never goes over 30 images? Ideally, if there are 20 images in the array and 11 new ones need to be added, all 11 new images should be appended while removing the oldest existing image.

javascript mongodb mongoose

Answer 1

Answer №1

To achieve this specific task, the $addToSet operator will not suffice. You have two viable options available:

If you want to ensure that only unique images are fetched, you can utilize the combination of $push along with the $slice operator.

User.findOneAndUpdate({ _id }, 
    { $push: { "instagram.images": { $each: arr, $slice: -30 } } });

In cases where unique images cannot be guaranteed, you need to retrieve the user data and filter the array in your code prior to updating:

let user = User.findOne({_id});
// Use a unique identifier for image uniqueness
let imagesIds = user.instagram.images.map(v => v.id);
let filteredImages = arr.filter((elem => !imagesIds.includes(elem.id)));

Finally, apply the approach from option 1 using filteredImages:

User.findOneAndUpdate({ _id }, 
    { $push: { "instagram.images": { $each: filteredImages, $slice: -30 } } });

It's important to note that mongoose typically generates an _id field for nested objects automatically, making the utility of $addToSet somewhat redundant in this context.

Answer 2

To achieve this specific task, the $addToSet operator will not suffice. You have two viable options available:

If you want to ensure that only unique images are fetched, you can utilize the combination of $push along with the $slice operator.

User.findOneAndUpdate({ _id }, 
    { $push: { "instagram.images": { $each: arr, $slice: -30 } } });

In cases where unique images cannot be guaranteed, you need to retrieve the user data and filter the array in your code prior to updating:

let user = User.findOne({_id});
// Use a unique identifier for image uniqueness
let imagesIds = user.instagram.images.map(v => v.id);
let filteredImages = arr.filter((elem => !imagesIds.includes(elem.id)));

Finally, apply the approach from option 1 using filteredImages:

User.findOneAndUpdate({ _id }, 
    { $push: { "instagram.images": { $each: filteredImages, $slice: -30 } } });

It's important to note that mongoose typically generates an _id field for nested objects automatically, making the utility of $addToSet somewhat redundant in this context.

Answer 3

Answer №2

If you follow the reasoning correctly, consider using the $size operator in this way:

const T = async () => {
  try {
     //If the array_field has more than 30 elements, the result document will not be found.
     let result = User.findOneAndUpdate({$expr: {$lte: [{$size: "$array_field"}, 30]}});
     if (!result) {
        //No documents meet the criteria
     } else {
       //You can add elements using a for loop, for example
       result.array_field.addToSet(element)
       //You can also check the length of array_field before saving it
       await result.save()
     }
  } catch (e) {
    console.error(e)
  }
}

If the array_field has less than 30 elements, it will be found and updated. You can also use $size in combination with comparison operators: $gte / $lte

$addToSet ensures that you update the array with unique values. You can verify this again before saving to the collection.

Answer 4

If you follow the reasoning correctly, consider using the $size operator in this way:

const T = async () => {
  try {
     //If the array_field has more than 30 elements, the result document will not be found.
     let result = User.findOneAndUpdate({$expr: {$lte: [{$size: "$array_field"}, 30]}});
     if (!result) {
        //No documents meet the criteria
     } else {
       //You can add elements using a for loop, for example
       result.array_field.addToSet(element)
       //You can also check the length of array_field before saving it
       await result.save()
     }
  } catch (e) {
    console.error(e)
  }
}

If the array_field has less than 30 elements, it will be found and updated. You can also use $size in combination with comparison operators: $gte / $lte

$addToSet ensures that you update the array with unique values. You can verify this again before saving to the collection.

Mongoose: Guaranteeing that the array will never surpass a specific limit of items

Answer №1

Answer №2

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