From 43b1e0c39171e207ff37a1e0d4844483bd6f3775 Mon Sep 17 00:00:00 2001
From: Stefan Majewsky <majewsky@gmx.net>
Date: Sat, 4 Jan 2025 16:13:45 +0100
Subject: add SQL support

---
 option/option.go      | 50 +++++++++++++++++++++++++++++++++++++++++++++-----
 option/option_test.go | 29 +++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+), 5 deletions(-)

(limited to 'option')

diff --git a/option/option.go b/option/option.go
index 1ea2e79..0f19bb5 100644
--- a/option/option.go
+++ b/option/option.go
@@ -113,9 +113,13 @@
 package option
 
 import (
+	"database/sql"
+	"database/sql/driver"
 	"encoding/json"
 	"fmt"
 	"iter"
+
+	"github.com/majewsky/gg/internal/hack"
 )
 
 // Option is a type that contains either one or no instances of T.
@@ -289,6 +293,16 @@ func (o Option[T]) Xor(other Option[T]) Option[T] {
 ////////////////////////////////////////////////////////////////////////////////
 // formatting/marshalling support
 
+// These are static assertions that Option implements the intended interfaces.
+// (The YAML interfaces are not checked because we don't want to add 3rd-party lib deps here.)
+var (
+	_ fmt.Formatter    = Option[bool]{}
+	_ sql.Scanner      = &Option[bool]{}
+	_ driver.Valuer    = Option[bool]{}
+	_ json.Marshaler   = Option[bool]{}
+	_ json.Unmarshaler = &Option[bool]{}
+)
+
 // Format implements the fmt.Formatter interface.
 //
 // If there is a contained value, it will be formatted as if it was given directly.
@@ -311,7 +325,33 @@ type yamlMarshaler interface {
 	MarshalYAML() (any, error)
 }
 
-// MarshalJSON implements the json.Marshaler interface.
+// Scan implements the database/sql.Scanner interface.
+func (o *Option[T]) Scan(src any) error {
+	switch src := src.(type) {
+	case nil:
+		*o = None[T]()
+		return nil
+	default:
+		var data T
+		err := hack.ConvertAssign(&data, src)
+		if err != nil {
+			return err
+		}
+		*o = Some(data)
+		return nil
+	}
+}
+
+// Value implements the database/sql/driver.Valuer interface.
+func (o Option[T]) Value() (driver.Value, error) {
+	if o.isSome {
+		return driver.DefaultParameterConverter.ConvertValue(o.value)
+	} else {
+		return nil, nil
+	}
+}
+
+// MarshalJSON implements the encoding/json.Marshaler interface.
 func (o Option[T]) MarshalJSON() ([]byte, error) {
 	if o.isSome {
 		return json.Marshal(o.value)
@@ -320,7 +360,7 @@ func (o Option[T]) MarshalJSON() ([]byte, error) {
 	}
 }
 
-// UnmarshalJSON implements the json.Unmarshaler interface.
+// UnmarshalJSON implements the encoding/json.Unmarshaler interface.
 func (o *Option[T]) UnmarshalJSON(buf []byte) error {
 	var data *T
 	err := json.Unmarshal(buf, &data)
@@ -331,7 +371,7 @@ func (o *Option[T]) UnmarshalJSON(buf []byte) error {
 	return nil
 }
 
-// MarshalYAML implements the yaml.Marshaler interface.
+// MarshalYAML implements the yaml.Marshaler interface from gopkg.in/yaml.v2 and v3.
 func (o Option[T]) MarshalYAML() (any, error) {
 	if o.isSome {
 		// If we just return o.value directly here, MarshalYAML will not be called
@@ -347,9 +387,9 @@ func (o Option[T]) MarshalYAML() (any, error) {
 	}
 }
 
-// UnmarshalYAML implements the yaml.Unmarshaler interface.
+// UnmarshalYAML implements the yaml.Unmarshaler interface from gopkg.in/yaml.v2.
 //
-// This function signature is compatible with both v2 and v3 of github.com/go-yaml/yaml,
+// gopkg.in/yaml.v3 supports this interface via backwards-compatibility,
 // so we intentionally do not use the v3-only signature that refers to the yaml.Node type.
 func (o *Option[T]) UnmarshalYAML(unmarshal func(any) error) error {
 	var data *T
diff --git a/option/option_test.go b/option/option_test.go
index 2bac4f5..80e8e84 100644
--- a/option/option_test.go
+++ b/option/option_test.go
@@ -146,6 +146,35 @@ func TestFormat(t *testing.T) {
 	AssertEqual(t, fmt.Sprintf("value is %#v", listOfOptions), "value is []option.Option[int]{<none>, 42}")
 }
 
+func TestMarshalSQL(t *testing.T) {
+	value, err := None[string]().Value()
+	AssertEqual(t, err, nil)
+	AssertEqual(t, value, nil)
+
+	value, err = Some("hello").Value()
+	AssertEqual(t, err, nil)
+	AssertEqual(t, value, "hello")
+
+	_, err = Some(struct{}{}).Value()
+	AssertEqual(t, err.Error(), "unsupported type struct {}, a struct")
+}
+
+func TestUnmarshalSQL(t *testing.T) {
+	var o1 Option[string]
+	err := o1.Scan(nil)
+	AssertEqual(t, err, nil)
+	AssertEqual(t, o1, None[string]())
+
+	var o2 Option[string]
+	err = o2.Scan("hello")
+	AssertEqual(t, err, nil)
+	AssertEqual(t, o2, Some("hello"))
+
+	var o3 Option[struct{}]
+	err = o3.Scan("hello")
+	AssertEqual(t, err.Error(), "unsupported Scan, storing driver.Value type string into type *struct {}")
+}
+
 func TestMarshalAndUnmarshalJSON(t *testing.T) {
 	type payload struct {
 		N1 Option[int] `json:"n1"`
-- 
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