mongodb - How does $addToSet specify a field as a check field for existence?

Question

There is a document, and one of its attributes is a document array. I want to add a document to the array. If it exists, it will not be added. How to judge whether it exists or not is that all attributes are the same. ? Can you specify an attribute
{_id:0,
user:[{id:1,name:a}]
}
For example, for the above record, I want to add data to user , if the id is 1, it means it already exists, so it will not be added, otherwise it will be added to the user array
$addToSet can achieve this requirement
Thank you

Answer 1

The uniqueness of the sub document you need cannot be achieved by $addToSet. There are two ideas for reference:

1. Try to create a composite unique index for business purposes

For example: create a unique composite index on name and user.id of the text {_id, name, number,user[{id,name}]}

2. Code control

db.test.update({ "_id" : ObjectId(""), "user.id" : {$ne : value }}, {$push : { user : { id : 1 , name : "a" }}})

db.test.update({ "_id" : ObjectId(""), "user.id" : {$nin : [] }}, {$push : { user : { id : 1 , name : "a" }}})

Use $ne or $nin before updating to determine whether the user.id exists in the existing id. If it does not exist, you can update.

For reference.

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