How to Handle Null Values in Golang Templates when Comparing with Slice Elements?

Handling Null Values in Golang Templates

Scenario

In Golang's database/sql package, Null[Type] structs help handle database values and their possible null values. However, testing for null values can be challenging. Using .Value to print SQL fields is straightforward, but evaluating against values in more complex scenarios can lead to issues.

Issue

Consider the following template code:

<select name="y">
   {{ range .SomeSlice }}
       <option value="{{ . }}" {{ if eq $.MyStruct.MyField.Value .}}selected="selected"{{ end }}></option>
   {{ end }}
</select>

This code attempts to set the selected attribute based on the equality of $.MyStruct.MyField.Value and .. However, if .MyField is not Valid, an error occurs.

Solution

There are two solutions to this issue.

Using Nested if Statements

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

Using the with Directive

<select name="y">
   {{range $idx, $e := .SomeSlice}}
       <option value="{{.}}">{{with $.MyStruct.MyField}}
               {{if eq .Value $e}}selected="selected"{{end}}
           {{end}}</option>
   {{end}}
</select>

Note:

Null[Type] structs are non-nil, so check the Valid field to determine if Value() will return a non-nil value.

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

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