From 368295d3ee4d8f08f30d5f8cb1841461cd4f14a6 Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <hi+github@yamlcoder.me>
Date: Sun, 12 Apr 2020 18:40:52 +0100
Subject: [PATCH] Create ROW helper for adhoc decoding of records

---
 composite_test.go | 13 +++++++++++++
 convert.go        | 28 ++++++++++++++++++++++++++++
 pgtype.go         |  9 +++++++++
 3 files changed, 50 insertions(+)

diff --git a/composite_test.go b/composite_test.go
index d51cb579..ffa7d479 100644
--- a/composite_test.go
+++ b/composite_test.go
@@ -71,7 +71,20 @@ create type mytype as (
 	}
 
 	fmt.Printf("Second row: %v\n", result)
+
+	// Adhoc rows can be decoded inplace without boilerplate (works with composite types too)
+	var isNull bool
+	var a int
+	var b *string
+
+	if err = conn.QueryRow(context.Background(), "select (2, 'bar')::mytype", pgx.QueryResultFormats{pgx.BinaryFormatCode}).Scan(pgtype.ROW(&isNull, &a, &b)); err != nil {
+		panic(err)
+	}
+
+	fmt.Printf("Adhoc: isNull=%v a=%d b=%s", isNull, a, *b)
+
 	// Output:
 	// First row: a=1 b=foo
 	// Second row: <nil>
+	// Adhoc: isNull=false a=2 b=bar
 }
diff --git a/convert.go b/convert.go
index a0c38c5b..8157358b 100644
--- a/convert.go
+++ b/convert.go
@@ -471,6 +471,34 @@ func ScanRowValue(ci *ConnInfo, src []byte, dst ...Value) error {
 	return nil
 }
 
+// ROW allows deconstructing row values (records and composite types) into
+// fields directly without creating your own type and implementing decoder interfaces
+func ROW(isNull *bool, fields ...interface{}) BinaryDecoderFunc {
+	return func(ci *ConnInfo, src []byte) error {
+		var record Record
+		if err := record.DecodeBinary(ci, src); err != nil {
+			return err
+		}
+
+		if record.Status == Null {
+			*isNull = true
+			return nil
+		}
+
+		if len(record.Fields) != len(fields) {
+			return errors.Errorf("can't scan row value, number of fields don't match: row fields count=%d desired fields count=%d", len(record.Fields), len(fields))
+		}
+
+		for i, f := range record.Fields {
+			if err := f.AssignTo(fields[i]); err != nil {
+				return err
+			}
+		}
+
+		return nil
+	}
+}
+
 func init() {
 	kindTypes = map[reflect.Kind]reflect.Type{
 		reflect.Bool:    reflect.TypeOf(false),
diff --git a/pgtype.go b/pgtype.go
index 914e02d2..1749c8c2 100644
--- a/pgtype.go
+++ b/pgtype.go
@@ -158,6 +158,15 @@ type TextEncoder interface {
 	EncodeText(ci *ConnInfo, buf []byte) (newBuf []byte, err error)
 }
 
+//The BinaryDecoderFunc type is an adapter to allow the use of ordinary functions as BinaryDecoder types.
+// If f is a function with the appropriate signature, BinaryDecoderFunc(f) is a BinaryDecoder that calls f.
+type BinaryDecoderFunc func(ci *ConnInfo, src []byte) error
+
+// DecodeBinary calls f(ci, src)
+func (f BinaryDecoderFunc) DecodeBinary(ci *ConnInfo, src []byte) error {
+	return f(ci, src)
+}
+
 var errUndefined = errors.New("cannot encode status undefined")
 var errBadStatus = errors.New("invalid status")