Validate two optional fields which should only be validated together

[makks129]

I have a struct with 2 fields: latitude and longitude
Both of them are optional, but if 1 is present the other should be validated as required
I haven't found a combination that would work to validate these 4 cases:

1.
lat=nil
lng=nil
Valid
2.
lat=123
lng=nil
Error
3.
lat=nil
lng=123
Error
4.
lat=123
lng=123
Valid

I tried different variations of required_ and excluded_ and omitempty but one of the cases always failed so far

Lat         string  `json:"lat" validate:"required_with=Inner.Lng,excluded_without=Inner.Lng,omitempty,latitude"`
Lng         string  `json:"lng" validate:"required_with=Inner.Lat,excluded_without=Inner.Lat,omitempty,longitude"`

It seems that it should be a fairly common case. Your help will be greatly appreciated!

[vynazevedo]

required_with on each field is enough here. Put it before omitempty, and refer to the sibling's Go field name:

type Coordinates struct {
    Lat *float64 `json:"lat" validate:"required_with=Lng,omitempty,latitude"`
    Lng *float64 `json:"lng" validate:"required_with=Lat,omitempty,longitude"`
}

With validate.Struct(...), that gives:

• Both nil: valid.
• Only one non-nil: the other fails required_with.
• Both present: both coordinate validators run.
• Both pointing to zero: valid; zero is a real coordinate.

The pointers distinguish a missing coordinate from zero. Your example declares strings, which can't be nil; if you keep strings, use the same tags and treat "" as missing.

If these fields live inside Inner, the tags still say Lng and Lat: they're looked up relative to the struct containing the fields. You don't need excluded_without as well.

One detail in the examples: latitude 123 should fail the latitude check even when longitude is present. Use something like 45, 123 to test the valid pair.

Checked with validator v10.27.0, including a containing struct with an Inner Coordinates field. The required_with documentation describes the presence check.