Develop Reference

How to perform mongoose deleteMany() with query operators?

I want to delete X number of posts starting from the most recently created for a specific user.
How can I apply this logic using mongoose so that I can perform just ONE database operation instead of first having to query for these posts and remove them one by one?
I am finding using the query and projection operators with the $ very confusing, any help would be appreciated.
Below I added pseudo code on how it should to work.
Thank you!
const userId = "123456"
const deleteCount = 6
const deletedPosts = await Post.deleteMany({
.where { userid == userId) }
.sort({createdAt: -1}) // delete by most recent
.limit(deleteCount) // only delete 6 (most recent) posts
}, {new: true}) // return results of operation
console.log(deletedPosts.deletedCount) // -> should be "6"

You can't set a limit when using deleteMany or findAndModify. So, if you want to precisely limit the number of documents removed, you'll need to do it in two steps.
db.getCollection('users').find({}, {class : 4}) .limit(2) .sort({StudentAge: -1}) .toArray() .map(function(doc) { return doc._id; }); //returns the array of id's
db.getCollection('users').deleteMany({_id: {$in: [ "s3", "s4" ]}})//put the array of id's

Javascript ForEach on Array of Arrays

I am looping through a collection of blog posts to firstly push the username and ID of the blog author to a new array of arrays, and then secondly, count the number of blogs from each author. The code below achieves this; however, in the new array, the username and author ID are no longer separate items in the array, but seem to be concatenated into a single string. I need to retain them as separate items as I need to use both separately; how can I amend the result to achieve this?
var countAuthors = [];
blogAuthors = await Blog.find().populate('authors');
blogAuthors.forEach(function(blogAuthor){
countAuthors.push([blogAuthor.author.username, blogAuthor.author.id]);
})
console.log(countAuthors);
// Outputs as separate array items, as expected:
// [ 'author1', 5d7eed028c298b424b3fb5f1 ],
// [ 'author2', 5dd8aa254d74b30017dbfdd3 ],
var result = {};
countAuthors.forEach(function(x) {
result[x] = (result[x] || 0) + 1;
});
console.log(result);
// Username and author ID become a single string and cannot be accessed as separate array items
// 'author1,5d7eed028c298b424b3fb5f1': 15,
// 'author2,5dd8aa254d74b30017dbfdd3': 2,
Update:
Maybe I can explain a bit further WHY on what to do this. What I am aiming for is a table which displays the blog author's name alongside the number of blogs they have written. However, I also want the author name to link to their profile page, which requires the blogAuthor.author.id to do so. Hence, I need to still be able to access the author username and ID separately after executing the count. Thanks

You could use String.split().
For example:
let result = 'author1,5d7eed028c298b424b3fb5f1'.split(',')
would set result to:
['author1' , '5d7eed028c298b424b3fb5f1']
You can then access them individually like:
result[1] //'5d7eed028c298b424b3fb5f1'

Your issue is that you weren't splitting the x up in the foreach callback, and so the whole array was being converted to a string and being used as the key when inserting into the results object.
You can use array destructuring to split the author name and blog id, and use them to optionally adding a new entry to the result object, and then update that result.
countAuthors = [
['author1', 'bookId1'],
['author2', 'bookId2'],
['author1', 'bookId3'],
['author1', 'bookId4'],
['author2', 'bookId5']
]
var result = {};
countAuthors.forEach(([author, id]) => {
if (result[author] === undefined) {
result[author] = {count: 0, blogIds: []};
}
result[author].count += 1;
result[author].blogIds.push(id);
});
console.log(result);

Update multiple documents / add keys and its values in to a new array

I have collection named inventory where I have multiple documents that has values for each doc
{ "apples": 2 ,"oranges": 3, "carrots": 5 }
{ "apples": 4, "oranges": 6, "carrots": 9 }
How do I update push all fruits in to a single array on multiple documents like so:
{ "fruits": { "apples":2 ,"oranges":3 }, "carrots": 5 }

First thing to note here is that the example you give is not an array but just a sub-document for "fruits" that has different keys. An "array" in MongoDB would look like this:
{ "fruits": [{ "apples":2 } , { "orange":3 }], "carrot": 5 }
Also, aside from the term "fruits" being subjective, as with no other identifier you would have to specify a "list" of things that qualify as fruits, the other thing to consider is that there is no actual way in MongoDB at present to refer to the existing value of a field when processing an update.
What that means is you need to .find() each document to retrieve the data in order to be able to work with the sort of "re-structure" that you want. This essentially means looping the results an performing an .update() operation for each document.
The Bulk API for MongoDB 2.6 and greater can be of some help here, where at least the "write" operations to the database can be sent in batches, rather than one at a time:
var bulk = db.collection.initializeOrderedBulkOp();
var count = 0;
var fruits = ["apples","oranges"];
var unset = {};
fruits.forEach(function(fruit) {
unset[fruit] = 1;
});
db.collection.find({}).forEach(function(doc) {
var fields = [];
fruits.forEach(function(fruit) {
if ( doc.hasOwnProperty(fruit) ) {
var subDoc = {};
subDoc[fruit] = doc[fruit];
fields.push(subDoc);
}
});
bulk.find({ "_id": doc._id }).updateOne({
"$unset": unset, "$push": { "fruits": { "$each": fields } }
});
count++;
if ( count % 1000 == 0 ) {
bulk.execute();
var bulk = db.collection.initializeOrderedBulkOp();
}
});
if ( count % 1000 != 0 )
bulk.execute();
That also uses the $each modifier for $push in order to add multiple array entries at once. The $unset operator can be safely called for fields that don't exist in the document so there is no need to check for their presence in the document as is otherwise required when constructing the array of elements to $push.
Of course if you actually want a document like what you gave an example of that is not actually an array, then you construct differently with the $set operator:
var fields = {};
fruits.forEach(function(fruit) {
if ( doc.hasOwnProperty(fruit) )
fields[fruit] = doc[fruit];
});
bulk.find({ "_id": doc._id }).updateOne({
"$unset": unset, "$set": { "fruits": fields }
});
Whatever the case is you need to loop the existing collection. There is no operation that allows you to "take" an existing value in a document and "use it" in order to set a new value from a server side perspective.

MongoDB: how to update n records based on ObjectID

I've created a Collection containing 1 million documents, and I'm trying to select 50000 of these records based on the ObjectID, and update one of the values (i'm working in Mongo shell, running on Ubuntu).
Is it possible to define a 50000 document range? It doesn't matter which documents are included in the 50000 range, I simply want to ringfence a definite number of records and run an update operation using the primary id so that I can measure the performance time.
The code I've tried to run doesn't work:
use Assignment
var _start = new Date()
db.FlightsDate.update({$set:{Airtime: 8888}}).limit(50000).hint({_id:1});
var _end = new Date();
print("Time to Bulk Update AirTime key for 50000 documents… " + ((_end _start)/1000));
...i'm gathering that MongoDB needs me to include a query in the command to specify which docs are to be updated (I now understand from reading other posts that .limit won't constrain the number of records than an .update writes to).
Please can anyone advise a method that'll enable me to define the number of records to be updated?
Grateful for advice.
R,
Jon

If you are simply looking for a "range" that covers 50,000 of the documents in the collection then your best approach is to query and find the "starting" and "ending" documents of your range first. Then apply that "range" specification to your update.
var start_id = db.FlightsDate.find({}).limit(1).toArray()[0]._id;
var end_id = db.FlightsDate.find({}).skip(49999).limit(1).toArray()[0]._id;
var _start = new Date();
db.FlightsDate.update(
{ "_id": { "$gte": start_id, "$lte": end_id } },
{ "$set"; { "Airtime": 8888 } },
{ "multi": true }
);
var _end = new Date();
( _end - _start )/1000;
If you then wanted the next 50,000 in an additional range then :
var start_id = db.FlightsDate.find(
{ "_id": { "$gt": end_id } }
).limit(1).toArray()[0]._id;
var end_id = db.FlightsDate.find(
{ "_id": { "$gt": end_id } }
).skip(49999).limit(1).toArray()[0]._id;
And do it all again.
The point is you need to know where to "start" and when to "end" within a range to limit your update to just 50,000 documents without any other criteria to do so.
Also note the usage of "multi" in the update method there. By default, .update() does not "update" any more than one document, essentially being the first match. So what you mean to do is update "all documents in the range" and that is why you need to apply "multi" here.

Multiple keys query in IndexedDB (Similar to OR in sql)

I have store with multiEntry index on tags.
{ tags: [ 'tag1', 'tag2', 'tag3' ] }
And i have query that also list of tags.
[ 'tag2', 'tag1', 'tag4' ]
I need to get all records which contain one of tag in query (Similar to SQL OR statement).
Currently I cannot find any other solution except iterate over tags in query and search by the each tag in the store.
Is there any better solution?
Thank you.

You cannot retrieve all results with one query except with iteration. You can optimize the search result by opening a index from the lowest value to the highest:
IDBKeyRange.bound ('tag1', 'tag4');
Other Indexed-Db feature you can use is to open multiple queries and combine the result when the queries complete. This way would be much faster than the iteration.

IndexedDB has only range query as Deni Mf answered.
OR query is simply union of multiple queries. That may be OK.
If you want efficient query, you have to iterate the cursor and seek the cursor position as necessary. Using my library, it will be
tags = ['tag2', 'tag1', 'tag4'];
tags.sort();
iter = new ydn.db.KeyIterator('store name', 'tags', IDBKeyRange.bound(tags[0], tags[tags.length-1]);
keys = [];
i = 0;
var req = db.open(iter, function(cursor) {
if (tags.indexOf(cursor.indexKey()) >= 0) {
// we got the result
if (keys.indexOf(cursor.key()) == -1) { // remove duplicate
keys.push(cursor.key());
}
} else {
return tags[++i]; // jump to next index position.
}
);
req.done(function() {
db.list('store name', keys).done(function(results) {
console.log(results);
}
});
Notice that the algorithm has no false positive retrieval. Key only query is performed first, so that we don't waste on de-serilization. The results is retrieved only we get all the primary keys after removing deplicates.