MongoDB add values to array if not exists

Question

I have this collection :

{
username : "user1",
arr : [
    {
        name : "test1",
        times : 0
    },
    {
        name : "test2",
        times : 5
    }
]
}

I have an array with some object. This objects have a name and the value times. Now I want to add new objects, if my array doesn't contain them. Example:

I have this two objects with the name "test1" and "test2" already in the collection. I want now to insert the objects "test2", "test3" and "test4". It should only add the object "test3" and "test4" to the array and not "test2" again. The value times doesn't do anything in this case, they should just have the value 0 when it gets insert.

Is there a way to do this with one query?

Will those objects you are adding have the times key as well? — chridam
– chridam, Commented Feb 8, 2017 at 14:58

Tarush Arora · Accepted Answer · 2017-02-09 00:09:35Z

19

If you can insert test1, test2,... one by one, then you can do something like this.

db.collection.update(
{username : "user1", 'arr.name': {$ne: 'test2'}}, 
{$push: {
     arr: {'name': 'test2', 'times': 0}
   }
})

The $ne condition will prevent the update if the name is already present in arr.

answered Feb 9, 2017 at 0:09

Tarush Arora

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2 Comments

user6586661 Over a year ago

Thank you, that will work. And a little other question. Can I update something else, if $ne prevents to insert my object?

Tarush Arora Over a year ago

@user6586661 Yes, you can specify in update parameter of the query, whatever you want to update.

Lazhar · Accepted Answer · 2017-12-21 12:51:40Z

4

You can now use the addToSet operator that is built just for that: adds a value to an array if it does not exist.

Documentation: https://docs.mongodb.com/manual/reference/operator/update/addToSet/

answered Dec 21, 2017 at 12:51

Lazhar

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1 Comment

Doradus Over a year ago

But that does not guarantee to preserve the order, unfortunately, so it's not equivalent.

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