Gorm return empty object instead default object when value is not found

Question

I made a MySQL query using GORM inside a little go app.

I have declared my domain struct

type Domain struct {
    gorm.Model
    Name string
    ...
}

Then when I send a query to MySQL with GORM with this method.

func DomainInfos(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    w.WriteHeader(http.StatusOK)

    var d Domain

    config.DbConnection.Where("name = ?", vars["domain"]).Find(&d)

    json.NewEncoder(w).Encode(d)
}

When the domain is not found it return an default object from my struct definition

{
    {0 0001-01-01 00:00:00 +0000 UTC 0001-01-01 00:00:00 +0000 UTC <nil>} 
    0
    0
    0
}

So I wrote a little condition to manually return an empty object

if d.ID == 0 {
    json.NewEncoder(w).Encode(make(map[string]string))
    return
}

Is it possible GORM return an empty object directly when the query return nothing, to avoid this manual checking ?

Adrian · Accepted Answer · 2018-12-07 15:05:28Z

5

GORM is returning an empty object; when it comes to Go values, "empty" and "default" are the same, and are actually called the zero value. In your situation, you're needing to control the JSON output, not the GORM return value.

You can add the omitempty tag to your fields to have them exluded from JSON output if they contain the zero value for their type:

type Domain struct {
    gorm.Model
    Name string `json:",omitempty"`
    ...
}

For each field with this tag, when you call Encode or Marshal, if the field contains its zero value (e.g. for Name, which is a string, if it is equal to ""), the field will not be included in the output. If you tag all the exported fields this way, and they all contain their zero values, the output will be an empty JSON object {}.

Also note that this:

json.NewEncoder(w).Encode(make(map[string]string))

Is equivalent to, but significantly less efficient than:

w.Write([]byte("{}"))

Your other option would be a custom marshal func, something like this:

func (d Domain) MarshalJSON() ([]byte, error) {
    if t.ID == 0 {
        return []byte("{}"), nil
    }

    // Wrap the type to avoid infinite recursion on MarshalJSON
    type dd Domain
    return json.Marshal(dd(d))
}

You can see a working sample here: https://play.golang.org/p/mIRfRKXeyyW

edited Dec 7, 2018 at 15:05

answered Dec 7, 2018 at 14:32

Adrian

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4 Comments

Jérôme Over a year ago

This is working for Name, ... but it still return the gorm.Model value. I also tried to add json:",omitempty" to gorm.Model without success

Adrian Over a year ago

If it's not omitting the field, then the field does not contain its type's zero value.

Jérôme Over a year ago

I think it's because gorm.Model extend my struct and add non omitted field.

Adrian Over a year ago

I've added another option in case the first does not work for your case. It's less intuitive but may help.

Avinash Ghadshi · Accepted Answer · 2023-02-26 12:31:07Z

1

omitempty does not work on the struct field of type time.Time

answered Feb 26, 2023 at 12:31

Avinash Ghadshi

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