How to Handle Type Conversions When Working with Databases in Go?

Golang Type Assertion: Handling Database Type Conversions

In Go, type assertions allow us to convert a value to a different type based on its actual type. This is useful when working with dynamic types or implementing custom interfaces.

Consider a scenario where we create a custom type called Role based on a string and wish to use it with a database driver. To do this, we need to implement the Valuer and Scanner interfaces.

However, while implementing these interfaces, we may encounter the error:

cannot convert value.(string) (type string) to type *Role

Solution for Scan Function:

The Scan function is used when retrieving data from a database. The issue arises because we are trying to convert the value of type string directly to a *Role pointer. Instead, we should dereference the r pointer and assign the value of value to it, like so:

func (r *Role) Scan(value interface{}) error {
    *r = Role(value.(string))
    return nil
}

Solution for Value Function:

The Value function is used when inserting or updating data in a database. The incorrect signature was provided earlier. The correct signature is:

func (r Role) Value() (driver.Value, error) {
    return string(r), nil
}

Note that this function doesn't handle or produce NULL values.

By following these corrections, we can successfully implement type conversion for our custom Role type when working with database drivers.

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