Mongo field null vs empty

Question

SQL has the convention of leaving fields as null when not present.

Is there a convention in Mongo to leave the field as null or use an empty value (such as an empty array) if the field is not set?

To be specific, I am using Go and Mongo 4.2 with the official Go mongo driver.

For example,

type A struct {
    ID string `bson:"_id"`

    Bs []B `bson:"bs"`
}

type B struct {
    ID string `bson:"_id"`
}

If an A does not have any Bs (Bs is empty), should it be defined as a zero-value ([]B(nil)) or as an empty array ([]B{}).

Note this affects the way the data is stored:

for zero-value

{
    "_id" : ...,
    "bs" : null
}

vs for empty value

{
    "_id" : ...,
    "bs" : [ ]
}

As well as construction before InsertOne (or insertion in general), since you would want to make sure memory is allocated beforehand for such objects.

There are even more than "null" and "empty": https://stackoverflow.com/questions/68255363/or-with-if-and-in-mongodb/68255564#68255564 — Wernfried Domscheit, Jan 01 '22 at 11:36

score 1 · Answer 1 · answered Jan 01 '22 at 01:47

1

In GO a string can not be null but a pointer to a string can be null so just use a pointer.

answered Jan 01 '22 at 01:47

DDMM

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Mongo field null vs empty

1 Answers1