How to Distinguish Between Unset and Empty Values in Go Structs?

Distinguishing Between Unset and Empty Values in Go Structs

In Go, when defining structs, you may encounter the need to distinguish between values that are intentionally unset and values that are simply empty. This can be critical for database persistence and ensuring accurate data handling.

Consider the following example:

<code class="go">type Organisation struct {
    Category string
    Code     string
    Name     string
}</code>

Let's say you want to determine if the Category field was never set or was intentionally set as an empty string. Using pointers for fields (e.g., *string) will not solve this problem, as the zero value for a pointer is nil, which cannot distinguish between an unset and an empty value.

To address this, you can utilize a custom type such as sql.NullString from the database/sql package. It keeps track of the NULL state and allows you to differentiate between the following scenarios:

• unset: NullString{String: "", Valid: false}
• empty string: NullString{String: "", Valid: true}
• non-empty string: NullString{String: "value", Valid: true}

During database scanning and parameter binding, the sql.NullString type handles the NULL state automatically.

For example, to scan into a NullString field:

<code class="go">err := db.QueryRow("SELECT category FROM organisations WHERE id = ?", id).Scan(&org.Category)</code>

To bind a NullString value to a database parameter:

<code class="go">_, err := db.Exec("INSERT INTO organisations (category) VALUES (?)", org.Category)</code>

This approach allows you to distinguish between unset and empty values and ensure accurate database persistence.

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