Empty Optional Parameters And alphanum

[smatric]

My endpoint accepts two optional parameters:

type Params struct {
	FYear  int    `form:"f-year" validate:"gt=1800,lt=2100"`
	FQuery string `form:"f-query" validate:"alphanum"`
}

However, validation fails on the field tagged as alphanum:

Error:Field validation for 'FQuery' failed on the 'alphanum' tag

How can I make the rule to be applied only when the field has a value?

[smatric]

Gin framework automatically assigns zero values to the fields corresponding to query string parameters that are missing. If I understand this correctly, this is why I cannot have an optional URL parameter and use validation rules such as "gt=1800" in the example above (because the value would be 0 if omitted).

If you could add support for a library such as gopkg.in/guregu/null.v4, it would solve the problem. I could define fields as nullable:

type Params struct {
	FYear  null.Int    `form:"f-year" validate:"gt=1800,lt=2100"`
	FQuery null.String `form:"f-query" validate:"alphanum"`
}

and, at the same time, apply validation that wouldn't be affected by zero values.

Please consider this feature request.

[deankarn]

Hey @smatric there are actually two ways to do what you want today :)

1. Use the omitempty tag and when the value is empty validator we skip all subsequent validations.
2. Register a CustomTypeFunc (Custom Type Function) to handle just like the sql.Null* types here in the tests.

let me know if this helps.

[smatric]

I somehow overlooked that. Thank you!