Add support for strict scan.

If there are unused columns in query result set Query method panics.

qrm/qrm.go

@@ -10,6 +10,21 @@ import (
 	"reflect"
 )
 
+// Config holds the configuration settings for QRM scanning behavior.
+type Config struct {
+	// StrictScan, when true, causes the scanning function to panic if it encounters any
+	// unused columns in the SQL query result. This ensures that every column is mapped
+	// to a field in the destination struct.
+	// Does not apply to statements build with SELECT_JSON_OBJ or SELECT_JSON_ARR
+	StrictScan bool
+}
+
+// GlobalConfig is the package-wide configuration for SQL scanning.
+// This variable should be modified only once, for instance, during application initialization.
+var GlobalConfig = Config{
+	StrictScan: false,
+}
+
 // ErrNoRows is returned by Query when query result set is empty
 var ErrNoRows = errors.New("qrm: no rows in result set")
 
@@ -199,12 +214,16 @@ func ScanOneRowToDest(scanContext *ScanContext, rows *sql.Rows, destPtr interfac
 
 	destValuePtr := reflect.ValueOf(destPtr)
 
+	scanContext.rowNum++
+
 	_, err = mapRowToStruct(scanContext, "", destValuePtr, nil)
 
 	if err != nil {
 		return fmt.Errorf("jet: failed to scan a row into destination, %w", err)
 	}
 
+	scanContext.EnsureEveryColumnRead() // can panic
+
 	return nil
 }
 
@@ -246,6 +265,10 @@ func queryToSlice(ctx context.Context, db Queryable, query string, args []interf
 		if err != nil {
 			return scanContext.rowNum, err
 		}
+
+		if scanContext.rowNum == 1 && GlobalConfig.StrictScan {
+			scanContext.EnsureEveryColumnRead()
+		}
 	}
 
 	err = rows.Close()

qrm/scan_context.go

@@ -17,7 +17,9 @@ type ScanContext struct {
 	groupKeyInfoCache        map[string]groupKeyInfo
 	typeInfoMap              map[string]typeInfo
 
-	typesVisited typeStack // to prevent circular dependency scan
+	typesVisited    typeStack // to prevent circular dependency scan
+	columnAlias     []string
+	columnIndexRead []bool
 }
 
 // NewScanContext creates new ScanContext from rows
@@ -57,9 +59,26 @@ func NewScanContext(rows *sql.Rows) (*ScanContext, error) {
 		typeInfoMap: make(map[string]typeInfo),
 
 		typesVisited: newTypeStack(),
+
+		columnAlias:     aliases,
+		columnIndexRead: make([]bool, len(aliases)),
 	}, nil
 }
 
+func (s *ScanContext) EnsureEveryColumnRead() {
+	var neverUsedColumns []string
+
+	for index, read := range s.columnIndexRead {
+		if !read {
+			neverUsedColumns = append(neverUsedColumns, `'`+s.columnAlias[index]+`'`)
+		}
+	}
+
+	if len(neverUsedColumns) > 0 {
+		panic("jet: columns never used: " + strings.Join(neverUsedColumns, ", "))
+	}
+}
+
 func createScanSlice(columnCount int) []interface{} {
 	scanPtrSlice := make([]interface{}, columnCount)
 
@@ -244,6 +263,9 @@ func (s *ScanContext) typeToColumnIndex(typeName, fieldName string) int {
 // rowElemValue always returns non-ptr value,
 // invalid value is nil
 func (s *ScanContext) rowElemValue(index int) reflect.Value {
+	if s.rowNum == 1 {
+		s.columnIndexRead[index] = true
+	}
 	scannedValue := reflect.ValueOf(s.row[index])
 	return scannedValue.Elem().Elem() // no need to check validity of Elem, because s.row[index] always contains interface in interface
 }