sdk: support for nullable model field types

sdk/nullable/nullable.go

@@ -0,0 +1,103 @@
+package nullable
+
+import (
+	"bytes"
+	"encoding/json"
+)
+
+type Type[T comparable] map[bool]T
+
+func Value[T comparable](t T) Type[T] {
+	var n Type[T]
+	n.Set(t)
+	return n
+}
+
+func NoZero[T comparable](t T) Type[T] {
+	var n Type[T]
+	n.SetNoZero(t)
+	return n
+}
+
+// Get retrieves the underlying value, if present, and returns nil if the value is null
+func (t Type[T]) Get() *T {
+	var empty T
+	if t.IsNull() {
+		return nil
+	}
+	if t.IsSpecified() {
+		ret := t[true]
+		return &ret
+	}
+	return &empty
+}
+
+// GetOrZero retrieves the underlying value, if present, and returns the zero value if null
+func (t Type[T]) GetOrZero() T {
+	var empty T
+	val := t.Get()
+	if val == nil {
+		return empty
+	}
+	return *val
+}
+
+// IsNull indicate whether the field was sent, and had a value of `null`
+func (t Type[T]) IsNull() bool {
+	_, foundNull := t[false]
+	return foundNull
+}
+
+// IsSpecified indicates whether the field was sent
+func (t Type[T]) IsSpecified() bool {
+	return len(t) != 0
+}
+
+// Set sets the underlying value to a given value
+func (t *Type[T]) Set(value T) {
+	*t = map[bool]T{true: value}
+}
+
+// SetNoZero sets the underlying value to a given value, whilst also nulling the field if it was set to
+// its zero value. This ensures that zero values are sent as null.
+func (t *Type[T]) SetNoZero(value T) {
+	var empty T
+	*t = map[bool]T{value != empty: value}
+}
+
+// SetNull indicate that the field was sent, and had a value of `null`
+func (t *Type[T]) SetNull() {
+	var empty T
+	*t = map[bool]T{false: empty}
+}
+
+// SetUnspecified indicate whether the field was sent
+func (t *Type[T]) SetUnspecified() {
+	*t = map[bool]T{}
+}
+
+func (t Type[T]) MarshalJSON() ([]byte, error) {
+	// note: if value was unspecified, and `omitempty` is set on the field tags, `json.Marshal` will omit this field
+	// if value was specified, and `null`, marshal it
+	if t.IsNull() {
+		return []byte("null"), nil
+	}
+	// otherwise, we have a value, so marshal it
+	return json.Marshal(t[true])
+}
+
+func (t *Type[T]) UnmarshalJSON(data []byte) error {
+	// note: if value is unspecified, UnmarshalJSON won't be called
+	// if value is specified and `null`
+	if bytes.Equal(data, []byte("null")) {
+		t.SetNull()
+		return nil
+	}
+	// otherwise, we have an actual value, so parse it
+	var val T
+	if err := json.Unmarshal(data, &val); err != nil {
+		return err
+	}
+	t.Set(val)
+	return nil
+}