How to Prevent Null Target Assignment When Mapping with Null Source in Struct?

How can I ensure that the target remains non-null when the source is null during struct mapping?

// Example in Go
func MapStruct(source *SourceStruct, target *TargetStruct) {
    if source == nil {
        return // Exit without modifying the target
    }
    target.Field1 = source.Field1
    target.Field2 = source.Field2
}

When mapping data between structs, if the source struct is null, it can lead to unintended consequences where the target structure may be set to null as well. In this answer, we will explore how to safeguard against such scenarios by employing appropriate checks and fail-safe mechanisms in your mapping logic.

// Improved mapping function in Go
func SafeMapStruct(source *SourceStruct, target *TargetStruct) {
    if source == nil {
        return // Prevent any assignment to the target struct
    }
    target.Field1 = source.Field1
    target.Field2 = source.Field2 // Continue assigning other fields

    // Ensure additional logical checks or transformations as needed
}

Causes

• Null source being passed directly to the mapping function.
• Unconditional assignment from the source to the target without checks.

Solutions

• Implement a check for null values at the start of the mapping function.
• Use a default state for the target struct that ensures it doesn't get set to null if the source is null.
• Leverage functional programming paradigms, such as Option types, to handle potential nulls more gracefully.

Mistake: Not checking if the source is null before proceeding with the mapping.

Solution: Always check for null sources and return early to avoid null assignments.

Mistake: Directly assigning fields from source to target without ensuring target is initialized.

Solution: Initialize the target struct properly before mapping to avoid unexpected nulls.