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say I have this array property ('articles') on a Mongoose schema:
articles: [ { kind: 'bear', hashtag: 'foo' }, { kind: 'llama', hashtag: 'baz', }, { kind: 'sheep', hashtag: 'bar', } ] how can I use
$addToSet https://docs.mongodb.org/manual/reference/operator/update/addToSet/
to add to this array by checking the value of hashtag to see if it's unique?
For example, if I want to add the following object to the above array, I want Mongo to 'reject' it as a duplicate:
{ kind: 'tortoise', hashtag: 'foo' } because hashtag=foo has already been taken.
The problem is that I only know how to use $addToSet with simple arrays of integers...
for example, if articles looked like this:
articles: [ 1 , 5 , 4, 2] I would use $addToSet like this:
var data = { "$addToSet": { "articles": 9 } } model.update(data); but how can I accomplish the same thing with an array of objects where the unique field is a string, in this case 'hashtag'? The docs don't make this clear and it seems like I have searched everywhere..
thanks
826
Learn how to update array fields in documents in MongoDB collections. You can use the updateOne() or updateMany() methods to add, update, or remove array elements based on the specified criteria. It is recommended to use the updateMany() method to update multiple arrays in a collection.
If the value is an array, $push appends the whole array as a single element. To add each element of the value separately, use the $each modifier with $push . For an example, see Append a Value to Arrays in Multiple Documents. For a list of modifiers available for $push , see Modifiers.
To remove an element, update, and use $pull in MongoDB. The $pull operator removes from an existing array all instances of a value or values that match a specified condition.
The $addToSet operator adds a value to an array unless the value is already present, in which case $addToSet does nothing to that array. The $addToSet operator has the form: { $addToSet: { <field1>: <value1>, ... } } To specify a <field> in an embedded document or in an array, use dot notation.
You need to use the $ne operator.
var data = { 'kind': 'tortoise', 'hashtag': 'foo' }; Model.update( { 'articles.hashtag': { '$ne': 'foo' } }, { '$addToSet': { 'articles': data } } ) This will update the document only if there is no sub document in the "article" array with the value of hashtag equals to "foo".
As @BlakesSeven mentioned in the comment
The
$addToSetbecomes irrelevant once you are testing for the presence of one of the values, so this may as well be a$pushfor code clarity. But the principle is correct since$addToSetworks on the whole object and not just part of it.
Model.update({ { 'articles.hashtag': { '$ne': 'foo' } }, { '$push': {'articles': data } } ) If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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