How to Check for Valid Fields in Go Templates with Null Types?

Testing for Valid Fields in Go Templates

In Go's database/sql package, Null types provide a mechanism to represent nullable database values. Determining whether a field within a struct is null (Valid is false) can be challenging in template expressions.

To print a SQL field's value, the .Value property is commonly used. However, when comparing a field's value with another value, issues can arise if the field is null. Directly testing for nil (e.g., if $.MyStruct.MyField == nil) will not work as the fields are not nil but rather empty Null structs.

The and function in Go templates evaluates all its arguments, even if the result is already determined. Therefore, using {{ if and ($.MyStruct.MyField) (eq $.MyStruct.MyField.Value .) }} will cause an error if $.MyStruct.MyField is null.

Instead, use nested {{ if }} statements to selectively evaluate expressions:

{{ if $.MyStruct.MyField }}
    {{ if eq $.MyStruct.MyField.Value . }}selected="selected"{{ end }}
{{ end }}

Alternately, employ the {{ with }} statement, but be aware that it sets the dot, requiring careful consideration:

{{ with $.MyStruct.MyField }}
    {{ if eq .Value $e }}selected="selected"{{ end }}
{{ end }}

Note that the examples above assume non-nullable values. For Null types, check the Valid field directly:

{{ if $.MyStruct.MyField.Valid }}
    {{ if eq $.MyStruct.MyField.Value . }}selected="selected"{{ end }}
{{ end }}

The above is the detailed content of How to Check for Valid Fields in Go Templates with Null Types?. For more information, please follow other related articles on the PHP Chinese website!