Mongoose push item to array if not exists

Question

I have a model schema like this:

Collection: {
    irrelevant fields,
    object: { 
        more irrelevant fields,
        array:
        [
            {
                field1,
                field2,
                _id: false
            }
        ]
    }
}

I want to push to array any object {field1, field2} that does not repeat with field1 already existing in array (in an updateOne query). field2 is constantly updating itself and i have tried addtoset but it considers field2 so it ends up adding another item i don't want to add.

For example:

array:[
    {field1: 1, field2: 6},
    {field1: 2, field2: 4},
    {field1: 3, field2: 1}
]

if i would want to push {field1: 2, field2: 6} it should not let me push it because the field1:2 already exists in array. (using addtoset, even it does check that the field1:2 already existis, it ends up adding te object because of field2 being different)

array:[
    {field1: 1, field2: 6},
    {field1: 2, field2: 4},
    {field1: 3, field2: 1}
    {field1: 2, field2: 6}
]

Joe · Accepted Answer · 2020-12-30 19:35:59Z

2

You could use the pipeline form of update with the $cond operator. If the field1 value already exists, keep the value of the array the same, if not, append the new value to the end.

Perhaps something similar to:

const newValue = {field1: 2, field2: 6};

db.collection.update({match criteria},
    [{$set:{
         array:{
             $cond:{
               if: {$in: [newValue.field1, "$array.field1"]},
               then: "$array",
               else: {$concatArrays: ["$array", [newValue]]}]}
             }
         }
     }}]
)

edited Dec 30, 2020 at 19:35

answered Dec 29, 2020 at 2:10

Joe

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2 Comments

Traoré Moussa Over a year ago

What if I need to update a value on the existing item in the array if the fild1 is indeed present ?

Joe Over a year ago

If the change is too complex to put on the then line, take a look at using $reduce

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