From 406888cdd515c5738777ddedd8d76a2842417da1 Mon Sep 17 00:00:00 2001
From: Gregory Eremin <g@erem.in>
Date: Tue, 3 Jul 2018 19:47:23 +0200
Subject: [PATCH] Extract column indexing into reflect2 package

---
 reflect2/fields.go    | 27 +++++++++++++++++++++++++++
 sqldb/query_result.go | 27 ++++++---------------------
 2 files changed, 33 insertions(+), 21 deletions(-)
 create mode 100644 reflect2/fields.go

diff --git a/reflect2/fields.go b/reflect2/fields.go
new file mode 100644
index 0000000..ccbdc5f
--- /dev/null
+++ b/reflect2/fields.go
@@ -0,0 +1,27 @@
+package reflect2
+
+import "reflect"
+
+// TagIndex returns a map that associates tag values with field indices.
+func TagIndex(typ reflect.Type, tag string) map[string]int {
+	tagIndex := map[string]int{}
+	for i := 0; i < typ.NumField(); i++ {
+		tag := typ.Field(i).Tag.Get(tag)
+		if tag != "" {
+			tagIndex[tag] = i
+		}
+	}
+	return tagIndex
+}
+
+// AssociateColumns returns a map that associates column indices with fields.
+func AssociateColumns(typ reflect.Type, tag string, cols []string) map[int]int {
+	tagIndex := TagIndex(typ, tag)
+	colFields := map[int]int{}
+	for i, col := range cols {
+		if fi, ok := tagIndex[col]; ok {
+			colFields[i] = fi
+		}
+	}
+	return colFields
+}
diff --git a/sqldb/query_result.go b/sqldb/query_result.go
index c33dff3..6340cac 100644
--- a/sqldb/query_result.go
+++ b/sqldb/query_result.go
@@ -4,6 +4,8 @@ import (
 	"database/sql"
 	"fmt"
 	"reflect"
+
+	"github.com/localhots/gobelt/reflect2"
 )
 
 // QueryResult ...
@@ -13,6 +15,8 @@ type QueryResult interface {
 	Rows() *sql.Rows
 }
 
+const tagName = "db"
+
 type queryResult struct {
 	err  error
 	rows *sql.Rows
@@ -177,7 +181,7 @@ func (r *queryResult) loadStruct(typ reflect.Type, dest interface{}) {
 
 	val := reflect.ValueOf(dest).Elem()
 	vals := make([]interface{}, len(cols))
-	tm := tagMap(cols, val.Type())
+	tm := reflect2.AssociateColumns(val.Type(), tagName, cols)
 	for i := range cols {
 		if fi, ok := tm[i]; ok {
 			fval := val.Field(fi)
@@ -210,7 +214,7 @@ func (r *queryResult) loadSliceOfStructs(typ reflect.Type, dest interface{}) {
 	vSlice := reflect.ValueOf(dest).Elem()
 	tSlice := vSlice.Type()
 	tElem := tSlice.Elem()
-	tm := tagMap(cols, tElem)
+	tm := reflect2.AssociateColumns(tElem, tagName, cols)
 
 	for r.rows.Next() {
 		vals := make([]interface{}, len(cols))
@@ -259,22 +263,3 @@ func newValue(typ *sql.ColumnType) interface{} {
 		panic(fmt.Errorf("Unsupported MySQL type: %s", typ.DatabaseTypeName()))
 	}
 }
-
-func tagMap(cols []string, typ reflect.Type) map[int]int {
-	fieldIndices := map[string]int{}
-	for i := 0; i < typ.NumField(); i++ {
-		tag := typ.Field(i).Tag.Get("db")
-		if tag != "" {
-			fieldIndices[tag] = i
-		}
-	}
-
-	colFields := map[int]int{}
-	for i, col := range cols {
-		if fi, ok := fieldIndices[col]; ok {
-			colFields[i] = fi
-		}
-	}
-
-	return colFields
-}