Merge pull request #22 from go-jet/err-no-rows

QRM returns sql.ErrNoRows when scanning into struct destination and query result set is empty.

README.md

@@ -11,7 +11,7 @@ Jet is a framework for writing type-safe SQL queries in Go, with ability to easi
 convert database query result into desired arbitrary object structure.  
 Jet currently supports `PostgreSQL`, `MySQL` and `MariaDB`. Future releases will add support for additional databases.
 
-![jet](https://github.com/go-jet/jet/wiki/image/jet.png)   
+![jet](https://github.com/go-jet/jet/wiki/image/jet.png)  
 Jet is the easiest and the fastest way to write complex SQL queries and map database query result 
 into complex object composition. __It is not an ORM.__ 
 

internal/jet/statement.go

@@ -15,10 +15,12 @@ type Statement interface {
 	DebugSql() (query string)
 
 	// Query executes statement over database connection db and stores row result in destination.
-	// Destination can be arbitrary structure
+	// Destination can be either pointer to struct or pointer to a slice.
+	// If destination is pointer to struct and query result set is empty, method returns sql.ErrNoRows.
 	Query(db qrm.DB, destination interface{}) error
 	// QueryContext executes statement with a context over database connection db and stores row result in destination.
-	// Destination can be of arbitrary structure
+	// Destination can be either pointer to struct or pointer to a slice.
+	// If destination is pointer to struct and query result set is empty, method returns sql.ErrNoRows.
 	QueryContext(context context.Context, db qrm.DB, destination interface{}) error
 
 	//Exec executes statement over db connection without returning any rows.

qrm/qrm.go

@@ -3,20 +3,14 @@ package qrm
 import (
 	"context"
 	"database/sql"
-	"database/sql/driver"
-	"fmt"
 	"github.com/go-jet/jet/internal/utils"
-	"github.com/go-jet/jet/qrm/internal"
-	"github.com/google/uuid"
 	"reflect"
-	"strconv"
-	"strings"
-	"time"
 )
 
 // Query executes Query Result Mapping (QRM) of `query` with list of parametrized arguments `arg` over database connection `db`
 // using context `ctx` into destination `destPtr`.
 // Destination can be either pointer to struct or pointer to slice of structs.
+// If destination is pointer to struct and query result set is empty, method returns sql.ErrNoRows.
 func Query(ctx context.Context, db DB, query string, args []interface{}, destPtr interface{}) error {
 
 	utils.MustBeInitializedPtr(db, "jet: db is nil")
@@ -26,17 +20,23 @@ func Query(ctx context.Context, db DB, query string, args []interface{}, destPtr
 	destinationPtrType := reflect.TypeOf(destPtr)
 
 	if destinationPtrType.Elem().Kind() == reflect.Slice {
-		return queryToSlice(ctx, db, query, args, destPtr)
+		_, err := queryToSlice(ctx, db, query, args, destPtr)
+		return err
 	} else if destinationPtrType.Elem().Kind() == reflect.Struct {
 		tempSlicePtrValue := reflect.New(reflect.SliceOf(destinationPtrType))
 		tempSliceValue := tempSlicePtrValue.Elem()
 
-		err := queryToSlice(ctx, db, query, args, tempSlicePtrValue.Interface())
+		rowsProcessed, err := queryToSlice(ctx, db, query, args, tempSlicePtrValue.Interface())
 
 		if err != nil {
 			return err
 		}
 
+		if rowsProcessed == 0 {
+			return sql.ErrNoRows
+		}
+
+		// edge case when row result set contains only NULLs.
 		if tempSliceValue.Len() == 0 {
 			return nil
 		}
@@ -53,7 +53,7 @@ func Query(ctx context.Context, db DB, query string, args []interface{}, destPtr
 	}
 }
 
-func queryToSlice(ctx context.Context, db DB, query string, args []interface{}, slicePtr interface{}) error {
+func queryToSlice(ctx context.Context, db DB, query string, args []interface{}, slicePtr interface{}) (rowsProcessed int64, err error) {
 	if ctx == nil {
 		ctx = context.Background()
 	}
@@ -61,27 +61,27 @@ func queryToSlice(ctx context.Context, db DB, query string, args []interface{},
 	rows, err := db.QueryContext(ctx, query, args...)
 
 	if err != nil {
-		return err
+		return
 	}
 	defer rows.Close()
 
 	scanContext, err := newScanContext(rows)
 
 	if err != nil {
-		return err
+		return
 	}
 
 	if len(scanContext.row) == 0 {
-		return nil
+		return
 	}
 
 	slicePtrValue := reflect.ValueOf(slicePtr)
 
 	for rows.Next() {
-		err := rows.Scan(scanContext.row...)
+		err = rows.Scan(scanContext.row...)
 
 		if err != nil {
-			return err
+			return
 		}
 
 		scanContext.rowNum++
@@ -89,22 +89,24 @@ func queryToSlice(ctx context.Context, db DB, query string, args []interface{},
 		_, err = mapRowToSlice(scanContext, "", slicePtrValue, nil)
 
 		if err != nil {
-			return err
+			return
 		}
 	}
 
 	err = rows.Close()
 	if err != nil {
-		return err
+		return
 	}
 
 	err = rows.Err()
 
 	if err != nil {
-		return err
+		return
 	}
 
-	return nil
+	rowsProcessed = scanContext.rowNum
+
+	return
 }
 
 func mapRowToSlice(scanContext *scanContext, groupKey string, slicePtrValue reflect.Value, field *reflect.StructField) (updated bool, err error) {
@@ -171,57 +173,8 @@ func mapRowToBaseTypeSlice(scanContext *scanContext, slicePtrValue reflect.Value
 	return
 }
 
-type typeInfo struct {
-	fieldMappings []fieldMapping
-}
-
-type fieldMapping struct {
-	complexType       bool
-	columnIndex       int
-	implementsScanner bool
-}
-
-func (s *scanContext) getTypeInfo(structType reflect.Type, parentField *reflect.StructField) typeInfo {
-
-	typeMapKey := structType.String()
-
-	if parentField != nil {
-		typeMapKey += string(parentField.Tag)
-	}
-
-	if typeInfo, ok := s.typeInfoMap[typeMapKey]; ok {
-		return typeInfo
-	}
-
-	typeName := getTypeName(structType, parentField)
-
-	newTypeInfo := typeInfo{}
-
-	for i := 0; i < structType.NumField(); i++ {
-		field := structType.Field(i)
-
-		newTypeName, fieldName := getTypeAndFieldName(typeName, field)
-		columnIndex := s.typeToColumnIndex(newTypeName, fieldName)
-
-		fieldMap := fieldMapping{
-			columnIndex: columnIndex,
-		}
-
-		if implementsScannerType(field.Type) {
-			fieldMap.implementsScanner = true
-		} else if !isSimpleModelType(field.Type) {
-			fieldMap.complexType = true
-		}
-
-		newTypeInfo.fieldMappings = append(newTypeInfo.fieldMappings, fieldMap)
-	}
-
-	s.typeInfoMap[typeMapKey] = newTypeInfo
-
-	return newTypeInfo
-}
-
 func mapRowToStruct(scanContext *scanContext, groupKey string, structPtrValue reflect.Value, parentField *reflect.StructField, onlySlices ...bool) (updated bool, err error) {
+	mapOnlySlices := len(onlySlices) > 0
 	structType := structPtrValue.Type().Elem()
 
 	typeInf := scanContext.getTypeInfo(structType, parentField)
@@ -250,22 +203,21 @@ func mapRowToStruct(scanContext *scanContext, groupKey string, structPtrValue re
 				updated = true
 			}
 
-		} else if len(onlySlices) == 0 {
+		} else {
-
+			if mapOnlySlices || fieldMap.columnIndex == -1 {
-			if fieldMap.columnIndex == -1 {
 				continue
 			}
 
+			cellValue := scanContext.rowElem(fieldMap.columnIndex)
+
+			if cellValue == nil {
+				continue
+			}
+
+			initializeValueIfNilPtr(fieldValue)
+			updated = true
+
 			if fieldMap.implementsScanner {
-
-				cellValue := scanContext.rowElem(fieldMap.columnIndex)
-
-				if cellValue == nil {
-					continue
-				}
-
-				initializeValueIfNilPtr(fieldValue)
-
 				scanner := getScanner(fieldValue)
 
 				err = scanner.Scan(cellValue)
@@ -273,15 +225,8 @@ func mapRowToStruct(scanContext *scanContext, groupKey string, structPtrValue re
 				if err != nil {
 					panic("jet: " + err.Error() + ", " + fieldToString(&field) + " of type " + structType.String())
 				}
-				updated = true
 			} else {
-				cellValue := scanContext.rowElem(fieldMap.columnIndex)
+				setReflectValue(reflect.ValueOf(cellValue), fieldValue)
-
-				if cellValue != nil {
-					updated = true
-					initializeValueIfNilPtr(fieldValue)
-					setReflectValue(reflect.ValueOf(cellValue), fieldValue)
-				}
 			}
 		}
 	}
@@ -289,21 +234,6 @@ func mapRowToStruct(scanContext *scanContext, groupKey string, structPtrValue re
 	return
 }
 
-func mapRowToDestinationPtr(scanContext *scanContext, groupKey string, destPtrValue reflect.Value, structField *reflect.StructField) (updated bool, err error) {
-
-	utils.ValueMustBe(destPtrValue, reflect.Ptr, "jet: internal error. Destination is not pointer.")
-
-	destValueKind := destPtrValue.Elem().Kind()
-
-	if destValueKind == reflect.Struct {
-		return mapRowToStruct(scanContext, groupKey, destPtrValue, structField)
-	} else if destValueKind == reflect.Slice {
-		return mapRowToSlice(scanContext, groupKey, destPtrValue, structField)
-	} else {
-		panic("jet: unsupported dest type: " + structField.Name + " " + structField.Type.String())
-	}
-}
-
 func mapRowToDestinationValue(scanContext *scanContext, groupKey string, dest reflect.Value, structField *reflect.StructField) (updated bool, err error) {
 
 	var destPtrValue reflect.Value
@@ -331,552 +261,17 @@ func mapRowToDestinationValue(scanContext *scanContext, groupKey string, dest re
 	return
 }
 
-var scannerInterfaceType = reflect.TypeOf((*sql.Scanner)(nil)).Elem()
+func mapRowToDestinationPtr(scanContext *scanContext, groupKey string, destPtrValue reflect.Value, structField *reflect.StructField) (updated bool, err error) {
 
-func implementsScannerType(fieldType reflect.Type) bool {
+	utils.ValueMustBe(destPtrValue, reflect.Ptr, "jet: internal error. Destination is not pointer.")
-	if fieldType.Implements(scannerInterfaceType) {
-		return true
-	}
 
-	typePtr := reflect.New(fieldType).Type()
+	destValueKind := destPtrValue.Elem().Kind()
 
-	return typePtr.Implements(scannerInterfaceType)
+	if destValueKind == reflect.Struct {
-}
+		return mapRowToStruct(scanContext, groupKey, destPtrValue, structField)
-
+	} else if destValueKind == reflect.Slice {
-func getScanner(value reflect.Value) sql.Scanner {
+		return mapRowToSlice(scanContext, groupKey, destPtrValue, structField)
-	if scanner, ok := value.Interface().(sql.Scanner); ok {
-		return scanner
-	}
-
-	return value.Addr().Interface().(sql.Scanner)
-}
-
-func getSliceElemType(slicePtrValue reflect.Value) reflect.Type {
-	sliceTypePtr := slicePtrValue.Type()
-
-	elemType := sliceTypePtr.Elem().Elem()
-
-	if elemType.Kind() == reflect.Ptr {
-		return elemType.Elem()
-	}
-
-	return elemType
-}
-
-func getSliceElemPtrAt(slicePtrValue reflect.Value, index int) reflect.Value {
-	sliceValue := slicePtrValue.Elem()
-	elem := sliceValue.Index(index)
-
-	if elem.Kind() == reflect.Ptr {
-		return elem
-	}
-
-	return elem.Addr()
-}
-
-func appendElemToSlice(slicePtrValue reflect.Value, objPtrValue reflect.Value) error {
-	if slicePtrValue.IsNil() {
-		panic("jet: internal, slice is nil")
-	}
-	sliceValue := slicePtrValue.Elem()
-	sliceElemType := sliceValue.Type().Elem()
-
-	newElemValue := objPtrValue
-
-	if sliceElemType.Kind() != reflect.Ptr {
-		newElemValue = objPtrValue.Elem()
-	}
-
-	if newElemValue.Type().ConvertibleTo(sliceElemType) {
-		newElemValue = newElemValue.Convert(sliceElemType)
-	}
-
-	if !newElemValue.Type().AssignableTo(sliceElemType) {
-		panic("jet: can't append " + newElemValue.Type().String() + " to " + sliceValue.Type().String() + " slice")
-	}
-
-	sliceValue.Set(reflect.Append(sliceValue, newElemValue))
-
-	return nil
-}
-
-func newElemPtrValueForSlice(slicePtrValue reflect.Value) reflect.Value {
-	destinationSliceType := slicePtrValue.Type().Elem()
-	elemType := indirectType(destinationSliceType.Elem())
-
-	return reflect.New(elemType)
-}
-
-func getTypeName(structType reflect.Type, parentField *reflect.StructField) string {
-	if parentField == nil {
-		return structType.Name()
-	}
-
-	aliasTag := parentField.Tag.Get("alias")
-
-	if aliasTag == "" {
-		return structType.Name()
-	}
-
-	aliasParts := strings.Split(aliasTag, ".")
-
-	return toCommonIdentifier(aliasParts[0])
-}
-
-func getTypeAndFieldName(structType string, field reflect.StructField) (string, string) {
-	aliasTag := field.Tag.Get("alias")
-
-	if aliasTag == "" {
-		return structType, field.Name
-	}
-
-	aliasParts := strings.Split(aliasTag, ".")
-
-	if len(aliasParts) == 1 {
-		return structType, toCommonIdentifier(aliasParts[0])
-	}
-
-	return toCommonIdentifier(aliasParts[0]), toCommonIdentifier(aliasParts[1])
-}
-
-var replacer = strings.NewReplacer(" ", "", "-", "", "_", "")
-
-func toCommonIdentifier(name string) string {
-	return strings.ToLower(replacer.Replace(name))
-}
-
-func initializeValueIfNilPtr(value reflect.Value) {
-
-	if !value.IsValid() || !value.CanSet() {
-		return
-	}
-
-	if value.Kind() == reflect.Ptr && value.IsNil() {
-		value.Set(reflect.New(value.Type().Elem()))
-	}
-}
-
-func valueToString(value reflect.Value) string {
-
-	if !value.IsValid() {
-		return "nil"
-	}
-
-	var valueInterface interface{}
-	if value.Kind() == reflect.Ptr {
-		if value.IsNil() {
-			return "nil"
-		}
-		valueInterface = value.Elem().Interface()
 	} else {
-		valueInterface = value.Interface()
+		panic("jet: unsupported dest type: " + structField.Name + " " + structField.Type.String())
-	}
-
-	if t, ok := valueInterface.(fmt.Stringer); ok {
-		return t.String()
-	}
-
-	return fmt.Sprintf("%#v", valueInterface)
-}
-
-var timeType = reflect.TypeOf(time.Now())
-var uuidType = reflect.TypeOf(uuid.New())
-
-func isSimpleModelType(objType reflect.Type) bool {
-	objType = indirectType(objType)
-
-	switch objType.Kind() {
-	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
-		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
-		reflect.Float32, reflect.Float64,
-		reflect.String,
-		reflect.Bool:
-		return true
-	case reflect.Slice:
-		return objType.Elem().Kind() == reflect.Uint8 //[]byte
-	case reflect.Struct:
-		return objType == timeType || objType == uuidType // time.Time || uuid.UUID
-	}
-
-	return false
-}
-
-func isIntegerType(value reflect.Type) bool {
-	switch value {
-	case int8Type, unit8Type, int16Type, uint16Type,
-		int32Type, uint32Type, int64Type, uint64Type:
-		return true
-	}
-
-	return false
-}
-
-func tryAssign(source, destination reflect.Value) bool {
-	if source.Type().ConvertibleTo(destination.Type()) {
-		source = source.Convert(destination.Type())
-	}
-
-	if isIntegerType(source.Type()) && destination.Type() == boolType {
-		intValue := source.Int()
-
-		if intValue == 1 {
-			source = reflect.ValueOf(true)
-		} else if intValue == 0 {
-			source = reflect.ValueOf(false)
-		}
-	}
-
-	if source.Type().AssignableTo(destination.Type()) {
-		destination.Set(source)
-		return true
-	}
-
-	return false
-}
-
-func setReflectValue(source, destination reflect.Value) {
-
-	if tryAssign(source, destination) {
-		return
-	}
-
-	if destination.Kind() == reflect.Ptr {
-		if source.Kind() == reflect.Ptr {
-			if !source.IsNil() {
-				if destination.IsNil() {
-					initializeValueIfNilPtr(destination)
-				}
-
-				if tryAssign(source.Elem(), destination.Elem()) {
-					return
-				}
-			} else {
-				return
-			}
-		} else {
-			if source.CanAddr() {
-				source = source.Addr()
-			} else {
-				sourceCopy := reflect.New(source.Type())
-				sourceCopy.Elem().Set(source)
-
-				source = sourceCopy
-			}
-
-			if tryAssign(source, destination) {
-				return
-			}
-
-			if tryAssign(source.Elem(), destination.Elem()) {
-				return
-			}
-		}
-	} else {
-		if source.Kind() == reflect.Ptr {
-			if source.IsNil() {
-				return
-			}
-			source = source.Elem()
-		}
-
-		if tryAssign(source, destination) {
-			return
-		}
-	}
-
-	panic("jet: can't set " + source.Type().String() + " to " + destination.Type().String())
-}
-
-func createScanValue(columnTypes []*sql.ColumnType) []interface{} {
-	values := make([]interface{}, len(columnTypes))
-
-	for i, sqlColumnType := range columnTypes {
-		columnType := newScanType(sqlColumnType)
-
-		columnValue := reflect.New(columnType)
-
-		values[i] = columnValue.Interface()
-	}
-
-	return values
-}
-
-var boolType = reflect.TypeOf(true)
-var int8Type = reflect.TypeOf(int8(1))
-var unit8Type = reflect.TypeOf(uint8(1))
-var int16Type = reflect.TypeOf(int16(1))
-var uint16Type = reflect.TypeOf(uint16(1))
-var int32Type = reflect.TypeOf(int32(1))
-var uint32Type = reflect.TypeOf(uint32(1))
-var int64Type = reflect.TypeOf(int64(1))
-var uint64Type = reflect.TypeOf(uint64(1))
-
-var nullBoolType = reflect.TypeOf(sql.NullBool{})
-var nullInt8Type = reflect.TypeOf(internal.NullInt8{})
-var nullInt16Type = reflect.TypeOf(internal.NullInt16{})
-var nullInt32Type = reflect.TypeOf(internal.NullInt32{})
-var nullInt64Type = reflect.TypeOf(sql.NullInt64{})
-var nullFloat32Type = reflect.TypeOf(internal.NullFloat32{})
-var nullFloat64Type = reflect.TypeOf(sql.NullFloat64{})
-var nullStringType = reflect.TypeOf(sql.NullString{})
-var nullTimeType = reflect.TypeOf(internal.NullTime{})
-var nullByteArrayType = reflect.TypeOf(internal.NullByteArray{})
-
-func newScanType(columnType *sql.ColumnType) reflect.Type {
-
-	switch columnType.DatabaseTypeName() {
-	case "TINYINT":
-		return nullInt8Type
-	case "INT2", "SMALLINT", "YEAR":
-		return nullInt16Type
-	case "INT4", "MEDIUMINT", "INT":
-		return nullInt32Type
-	case "INT8", "BIGINT":
-		return nullInt64Type
-	case "CHAR", "VARCHAR", "TEXT", "", "_TEXT", "TSVECTOR", "BPCHAR", "UUID", "JSON", "JSONB", "INTERVAL", "POINT", "BIT", "VARBIT", "XML":
-		return nullStringType
-	case "FLOAT4":
-		return nullFloat32Type
-	case "FLOAT8", "NUMERIC", "DECIMAL", "FLOAT", "DOUBLE":
-		return nullFloat64Type
-	case "BOOL":
-		return nullBoolType
-	case "BYTEA", "BINARY", "VARBINARY", "BLOB":
-		return nullByteArrayType
-	case "DATE", "DATETIME", "TIMESTAMP", "TIMESTAMPTZ", "TIME", "TIMETZ":
-		return nullTimeType
-	default:
-		return nullStringType
 	}
 }
-
-type scanContext struct {
-	rowNum int
-
-	row                  []interface{}
-	uniqueDestObjectsMap map[string]int
-
-	typeToColumnIndexMap map[string]int
-
-	groupKeyInfoCache map[string]groupKeyInfo
-
-	typeInfoMap map[string]typeInfo
-}
-
-func newScanContext(rows *sql.Rows) (*scanContext, error) {
-	aliases, err := rows.Columns()
-
-	if err != nil {
-		return nil, err
-	}
-
-	columnTypes, err := rows.ColumnTypes()
-
-	if err != nil {
-		return nil, err
-	}
-
-	typeToIndexMap := map[string]int{}
-
-	for i, alias := range aliases {
-		names := strings.SplitN(alias, ".", 2)
-
-		goName := toCommonIdentifier(names[0])
-
-		if len(names) > 1 {
-			goName += "." + toCommonIdentifier(names[1])
-		}
-
-		typeToIndexMap[strings.ToLower(goName)] = i
-	}
-
-	return &scanContext{
-		row:                  createScanValue(columnTypes),
-		uniqueDestObjectsMap: make(map[string]int),
-
-		groupKeyInfoCache:    make(map[string]groupKeyInfo),
-		typeToColumnIndexMap: typeToIndexMap,
-
-		typeInfoMap: make(map[string]typeInfo),
-	}, nil
-}
-
-type groupKeyInfo struct {
-	typeName string
-	indexes  []int
-	subTypes []groupKeyInfo
-}
-
-func (s *scanContext) getGroupKey(structType reflect.Type, structField *reflect.StructField) string {
-
-	mapKey := structType.Name()
-
-	if structField != nil {
-		mapKey += structField.Type.String()
-	}
-
-	if groupKeyInfo, ok := s.groupKeyInfoCache[mapKey]; ok {
-		return s.constructGroupKey(groupKeyInfo)
-	}
-
-	groupKeyInfo := s.getGroupKeyInfo(structType, structField)
-
-	s.groupKeyInfoCache[mapKey] = groupKeyInfo
-
-	return s.constructGroupKey(groupKeyInfo)
-}
-
-func (s *scanContext) constructGroupKey(groupKeyInfo groupKeyInfo) string {
-	if len(groupKeyInfo.indexes) == 0 && len(groupKeyInfo.subTypes) == 0 {
-		return "|ROW: " + strconv.Itoa(s.rowNum) + "|"
-	}
-
-	groupKeys := []string{}
-
-	for _, index := range groupKeyInfo.indexes {
-		cellValue := s.rowElem(index)
-		subKey := valueToString(reflect.ValueOf(cellValue))
-
-		groupKeys = append(groupKeys, subKey)
-	}
-
-	subTypesGroupKeys := []string{}
-	for _, subType := range groupKeyInfo.subTypes {
-		subTypesGroupKeys = append(subTypesGroupKeys, s.constructGroupKey(subType))
-	}
-
-	return groupKeyInfo.typeName + "(" + strings.Join(groupKeys, ",") + strings.Join(subTypesGroupKeys, ",") + ")"
-}
-
-func (s *scanContext) getGroupKeyInfo(structType reflect.Type, parentField *reflect.StructField) groupKeyInfo {
-	ret := groupKeyInfo{typeName: structType.Name()}
-
-	typeName := getTypeName(structType, parentField)
-	primaryKeyOverwrites := parentFieldPrimaryKeyOverwrite(parentField)
-
-	for i := 0; i < structType.NumField(); i++ {
-		field := structType.Field(i)
-		fieldType := indirectType(field.Type)
-
-		if !isSimpleModelType(fieldType) {
-			if fieldType.Kind() != reflect.Struct {
-				continue
-			}
-
-			subType := s.getGroupKeyInfo(fieldType, &field)
-
-			if len(subType.indexes) != 0 || len(subType.subTypes) != 0 {
-				ret.subTypes = append(ret.subTypes, subType)
-			}
-		} else {
-			if isPrimaryKey(field, primaryKeyOverwrites) {
-				newTypeName, fieldName := getTypeAndFieldName(typeName, field)
-
-				index := s.typeToColumnIndex(newTypeName, fieldName)
-
-				if index < 0 {
-					continue
-				}
-
-				ret.indexes = append(ret.indexes, index)
-			}
-		}
-	}
-
-	return ret
-}
-
-func (s *scanContext) typeToColumnIndex(typeName, fieldName string) int {
-	var key string
-
-	if typeName != "" {
-		key = strings.ToLower(typeName + "." + fieldName)
-	} else {
-		key = strings.ToLower(fieldName)
-	}
-
-	index, ok := s.typeToColumnIndexMap[key]
-
-	if !ok {
-		return -1
-	}
-
-	return index
-}
-
-func (s *scanContext) rowElem(index int) interface{} {
-
-	valuer, ok := s.row[index].(driver.Valuer)
-
-	if !ok {
-		panic("jet: internal error, scan value doesn't implement driver.Valuer")
-	}
-
-	value, err := valuer.Value()
-
-	utils.PanicOnError(err)
-
-	return value
-}
-
-func (s *scanContext) rowElemValuePtr(index int) reflect.Value {
-	rowElem := s.rowElem(index)
-	rowElemValue := reflect.ValueOf(rowElem)
-
-	if rowElemValue.Kind() == reflect.Ptr {
-		return rowElemValue
-	}
-
-	if rowElemValue.CanAddr() {
-		return rowElemValue.Addr()
-	}
-
-	newElem := reflect.New(rowElemValue.Type())
-	newElem.Elem().Set(rowElemValue)
-	return newElem
-}
-
-func isPrimaryKey(field reflect.StructField, primaryKeyOverwrites []string) bool {
-	if len(primaryKeyOverwrites) > 0 {
-		return utils.StringSliceContains(primaryKeyOverwrites, field.Name)
-	}
-
-	sqlTag := field.Tag.Get("sql")
-
-	return sqlTag == "primary_key"
-}
-
-func parentFieldPrimaryKeyOverwrite(parentField *reflect.StructField) []string {
-	if parentField == nil {
-		return nil
-	}
-
-	sqlTag := parentField.Tag.Get("sql")
-
-	if !strings.HasPrefix(sqlTag, "primary_key") {
-		return nil
-	}
-
-	parts := strings.Split(sqlTag, "=")
-
-	if len(parts) < 2 {
-		return nil
-	}
-
-	return strings.Split(parts[1], ",")
-}
-
-func indirectType(reflectType reflect.Type) reflect.Type {
-	if reflectType.Kind() != reflect.Ptr {
-		return reflectType
-	}
-	return reflectType.Elem()
-}
-
-func fieldToString(field *reflect.StructField) string {
-	if field == nil {
-		return ""
-	}
-
-	return " at '" + field.Name + " " + field.Type.String() + "'"
-}

qrm/scan_context.go

@@ -0,0 +1,241 @@
+package qrm
+
+import (
+	"database/sql"
+	"database/sql/driver"
+	"fmt"
+	"github.com/go-jet/jet/internal/utils"
+	"reflect"
+	"strings"
+)
+
+type scanContext struct {
+	rowNum                   int64
+	row                      []interface{}
+	uniqueDestObjectsMap     map[string]int
+	commonIdentToColumnIndex map[string]int
+	groupKeyInfoCache        map[string]groupKeyInfo
+	typeInfoMap              map[string]typeInfo
+}
+
+func newScanContext(rows *sql.Rows) (*scanContext, error) {
+	aliases, err := rows.Columns()
+
+	if err != nil {
+		return nil, err
+	}
+
+	columnTypes, err := rows.ColumnTypes()
+
+	if err != nil {
+		return nil, err
+	}
+
+	commonIdentToColumnIndex := map[string]int{}
+
+	for i, alias := range aliases {
+		names := strings.SplitN(alias, ".", 2)
+		commonIdentifier := toCommonIdentifier(names[0])
+
+		if len(names) > 1 {
+			commonIdentifier += "." + toCommonIdentifier(names[1])
+		}
+
+		commonIdentToColumnIndex[commonIdentifier] = i
+	}
+
+	return &scanContext{
+		row:                  createScanValue(columnTypes),
+		uniqueDestObjectsMap: make(map[string]int),
+
+		groupKeyInfoCache:        make(map[string]groupKeyInfo),
+		commonIdentToColumnIndex: commonIdentToColumnIndex,
+
+		typeInfoMap: make(map[string]typeInfo),
+	}, nil
+}
+
+type typeInfo struct {
+	fieldMappings []fieldMapping
+}
+
+type fieldMapping struct {
+	complexType       bool // slice or struct
+	columnIndex       int
+	implementsScanner bool
+}
+
+func (s *scanContext) getTypeInfo(structType reflect.Type, parentField *reflect.StructField) typeInfo {
+
+	typeMapKey := structType.String()
+
+	if parentField != nil {
+		typeMapKey += string(parentField.Tag)
+	}
+
+	if typeInfo, ok := s.typeInfoMap[typeMapKey]; ok {
+		return typeInfo
+	}
+
+	typeName := getTypeName(structType, parentField)
+
+	newTypeInfo := typeInfo{}
+
+	for i := 0; i < structType.NumField(); i++ {
+		field := structType.Field(i)
+
+		newTypeName, fieldName := getTypeAndFieldName(typeName, field)
+		columnIndex := s.typeToColumnIndex(newTypeName, fieldName)
+
+		fieldMap := fieldMapping{
+			columnIndex: columnIndex,
+		}
+
+		if implementsScannerType(field.Type) {
+			fieldMap.implementsScanner = true
+		} else if !isSimpleModelType(field.Type) {
+			fieldMap.complexType = true
+		}
+
+		newTypeInfo.fieldMappings = append(newTypeInfo.fieldMappings, fieldMap)
+	}
+
+	s.typeInfoMap[typeMapKey] = newTypeInfo
+
+	return newTypeInfo
+}
+
+type groupKeyInfo struct {
+	typeName string
+	indexes  []int
+	subTypes []groupKeyInfo
+}
+
+func (s *scanContext) getGroupKey(structType reflect.Type, structField *reflect.StructField) string {
+
+	mapKey := structType.Name()
+
+	if structField != nil {
+		mapKey += structField.Type.String()
+	}
+
+	if groupKeyInfo, ok := s.groupKeyInfoCache[mapKey]; ok {
+		return s.constructGroupKey(groupKeyInfo)
+	}
+
+	groupKeyInfo := s.getGroupKeyInfo(structType, structField)
+
+	s.groupKeyInfoCache[mapKey] = groupKeyInfo
+
+	return s.constructGroupKey(groupKeyInfo)
+}
+
+func (s *scanContext) constructGroupKey(groupKeyInfo groupKeyInfo) string {
+	if len(groupKeyInfo.indexes) == 0 && len(groupKeyInfo.subTypes) == 0 {
+		return fmt.Sprintf("|ROW:%d|", s.rowNum)
+	}
+
+	groupKeys := []string{}
+
+	for _, index := range groupKeyInfo.indexes {
+		cellValue := s.rowElem(index)
+		subKey := valueToString(reflect.ValueOf(cellValue))
+
+		groupKeys = append(groupKeys, subKey)
+	}
+
+	subTypesGroupKeys := []string{}
+	for _, subType := range groupKeyInfo.subTypes {
+		subTypesGroupKeys = append(subTypesGroupKeys, s.constructGroupKey(subType))
+	}
+
+	return groupKeyInfo.typeName + "(" + strings.Join(groupKeys, ",") + strings.Join(subTypesGroupKeys, ",") + ")"
+}
+
+func (s *scanContext) getGroupKeyInfo(structType reflect.Type, parentField *reflect.StructField) groupKeyInfo {
+	ret := groupKeyInfo{typeName: structType.Name()}
+
+	typeName := getTypeName(structType, parentField)
+	primaryKeyOverwrites := parentFieldPrimaryKeyOverwrite(parentField)
+
+	for i := 0; i < structType.NumField(); i++ {
+		field := structType.Field(i)
+		fieldType := indirectType(field.Type)
+
+		if !isSimpleModelType(fieldType) {
+			if fieldType.Kind() != reflect.Struct {
+				continue
+			}
+
+			subType := s.getGroupKeyInfo(fieldType, &field)
+
+			if len(subType.indexes) != 0 || len(subType.subTypes) != 0 {
+				ret.subTypes = append(ret.subTypes, subType)
+			}
+		} else {
+			if isPrimaryKey(field, primaryKeyOverwrites) {
+				newTypeName, fieldName := getTypeAndFieldName(typeName, field)
+
+				index := s.typeToColumnIndex(newTypeName, fieldName)
+
+				if index < 0 {
+					continue
+				}
+
+				ret.indexes = append(ret.indexes, index)
+			}
+		}
+	}
+
+	return ret
+}
+
+func (s *scanContext) typeToColumnIndex(typeName, fieldName string) int {
+	var key string
+
+	if typeName != "" {
+		key = strings.ToLower(typeName + "." + fieldName)
+	} else {
+		key = strings.ToLower(fieldName)
+	}
+
+	index, ok := s.commonIdentToColumnIndex[key]
+
+	if !ok {
+		return -1
+	}
+
+	return index
+}
+
+func (s *scanContext) rowElem(index int) interface{} {
+
+	valuer, ok := s.row[index].(driver.Valuer)
+
+	if !ok {
+		panic("jet: internal error, scan value doesn't implement driver.Valuer")
+	}
+
+	value, err := valuer.Value()
+
+	utils.PanicOnError(err)
+
+	return value
+}
+
+func (s *scanContext) rowElemValuePtr(index int) reflect.Value {
+	rowElem := s.rowElem(index)
+	rowElemValue := reflect.ValueOf(rowElem)
+
+	if rowElemValue.Kind() == reflect.Ptr {
+		return rowElemValue
+	}
+
+	if rowElemValue.CanAddr() {
+		return rowElemValue.Addr()
+	}
+
+	newElem := reflect.New(rowElemValue.Type())
+	newElem.Elem().Set(rowElemValue)
+	return newElem
+}

qrm/utill.go

@@ -0,0 +1,371 @@
+package qrm
+
+import (
+	"database/sql"
+	"fmt"
+	"github.com/go-jet/jet/internal/utils"
+	"github.com/go-jet/jet/qrm/internal"
+	"github.com/google/uuid"
+	"reflect"
+	"strings"
+	"time"
+)
+
+var scannerInterfaceType = reflect.TypeOf((*sql.Scanner)(nil)).Elem()
+
+func implementsScannerType(fieldType reflect.Type) bool {
+	if fieldType.Implements(scannerInterfaceType) {
+		return true
+	}
+
+	typePtr := reflect.New(fieldType).Type()
+
+	return typePtr.Implements(scannerInterfaceType)
+}
+
+func getScanner(value reflect.Value) sql.Scanner {
+	if scanner, ok := value.Interface().(sql.Scanner); ok {
+		return scanner
+	}
+
+	return value.Addr().Interface().(sql.Scanner)
+}
+
+func getSliceElemType(slicePtrValue reflect.Value) reflect.Type {
+	sliceTypePtr := slicePtrValue.Type()
+	elemType := indirectType(sliceTypePtr).Elem()
+
+	return indirectType(elemType)
+}
+
+func getSliceElemPtrAt(slicePtrValue reflect.Value, index int) reflect.Value {
+	sliceValue := slicePtrValue.Elem()
+	elem := sliceValue.Index(index)
+
+	if elem.Kind() == reflect.Ptr {
+		return elem
+	}
+
+	return elem.Addr()
+}
+
+func appendElemToSlice(slicePtrValue reflect.Value, objPtrValue reflect.Value) error {
+	if slicePtrValue.IsNil() {
+		panic("jet: internal, slice is nil")
+	}
+	sliceValue := slicePtrValue.Elem()
+	sliceElemType := sliceValue.Type().Elem()
+
+	newElemValue := objPtrValue
+
+	if sliceElemType.Kind() != reflect.Ptr {
+		newElemValue = objPtrValue.Elem()
+	}
+
+	if newElemValue.Type().ConvertibleTo(sliceElemType) {
+		newElemValue = newElemValue.Convert(sliceElemType)
+	}
+
+	if !newElemValue.Type().AssignableTo(sliceElemType) {
+		panic("jet: can't append " + newElemValue.Type().String() + " to " + sliceValue.Type().String() + " slice")
+	}
+
+	sliceValue.Set(reflect.Append(sliceValue, newElemValue))
+
+	return nil
+}
+
+func newElemPtrValueForSlice(slicePtrValue reflect.Value) reflect.Value {
+	destinationSliceType := slicePtrValue.Type().Elem()
+	elemType := indirectType(destinationSliceType.Elem())
+
+	return reflect.New(elemType)
+}
+
+func getTypeName(structType reflect.Type, parentField *reflect.StructField) string {
+	if parentField == nil {
+		return structType.Name()
+	}
+
+	aliasTag := parentField.Tag.Get("alias")
+
+	if aliasTag == "" {
+		return structType.Name()
+	}
+
+	aliasParts := strings.Split(aliasTag, ".")
+
+	return toCommonIdentifier(aliasParts[0])
+}
+
+func getTypeAndFieldName(structType string, field reflect.StructField) (string, string) {
+	aliasTag := field.Tag.Get("alias")
+
+	if aliasTag == "" {
+		return structType, field.Name
+	}
+
+	aliasParts := strings.Split(aliasTag, ".")
+
+	if len(aliasParts) == 1 {
+		return structType, toCommonIdentifier(aliasParts[0])
+	}
+
+	return toCommonIdentifier(aliasParts[0]), toCommonIdentifier(aliasParts[1])
+}
+
+var replacer = strings.NewReplacer(" ", "", "-", "", "_", "")
+
+func toCommonIdentifier(name string) string {
+	return strings.ToLower(replacer.Replace(name))
+}
+
+func initializeValueIfNilPtr(value reflect.Value) {
+
+	if !value.IsValid() || !value.CanSet() {
+		return
+	}
+
+	if value.Kind() == reflect.Ptr && value.IsNil() {
+		value.Set(reflect.New(value.Type().Elem()))
+	}
+}
+
+func valueToString(value reflect.Value) string {
+
+	if !value.IsValid() {
+		return "nil"
+	}
+
+	var valueInterface interface{}
+	if value.Kind() == reflect.Ptr {
+		if value.IsNil() {
+			return "nil"
+		}
+		valueInterface = value.Elem().Interface()
+	} else {
+		valueInterface = value.Interface()
+	}
+
+	if t, ok := valueInterface.(fmt.Stringer); ok {
+		return t.String()
+	}
+
+	return fmt.Sprintf("%#v", valueInterface)
+}
+
+var timeType = reflect.TypeOf(time.Now())
+var uuidType = reflect.TypeOf(uuid.New())
+
+func isSimpleModelType(objType reflect.Type) bool {
+	objType = indirectType(objType)
+
+	switch objType.Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
+		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
+		reflect.Float32, reflect.Float64,
+		reflect.String,
+		reflect.Bool:
+		return true
+	case reflect.Slice:
+		return objType.Elem().Kind() == reflect.Uint8 //[]byte
+	case reflect.Struct:
+		return objType == timeType || objType == uuidType // time.Time || uuid.UUID
+	}
+
+	return false
+}
+
+func isIntegerType(value reflect.Type) bool {
+	switch value {
+	case int8Type, unit8Type, int16Type, uint16Type,
+		int32Type, uint32Type, int64Type, uint64Type:
+		return true
+	}
+
+	return false
+}
+
+func tryAssign(source, destination reflect.Value) bool {
+	if source.Type().ConvertibleTo(destination.Type()) {
+		source = source.Convert(destination.Type())
+	}
+
+	if isIntegerType(source.Type()) && destination.Type() == boolType {
+		intValue := source.Int()
+
+		if intValue == 1 {
+			source = reflect.ValueOf(true)
+		} else if intValue == 0 {
+			source = reflect.ValueOf(false)
+		}
+	}
+
+	if source.Type().AssignableTo(destination.Type()) {
+		destination.Set(source)
+		return true
+	}
+
+	return false
+}
+
+func setReflectValue(source, destination reflect.Value) {
+
+	if tryAssign(source, destination) {
+		return
+	}
+
+	if destination.Kind() == reflect.Ptr {
+		if source.Kind() == reflect.Ptr {
+			if !source.IsNil() {
+				if destination.IsNil() {
+					initializeValueIfNilPtr(destination)
+				}
+
+				if tryAssign(source.Elem(), destination.Elem()) {
+					return
+				}
+			} else {
+				return
+			}
+		} else {
+			if source.CanAddr() {
+				source = source.Addr()
+			} else {
+				sourceCopy := reflect.New(source.Type())
+				sourceCopy.Elem().Set(source)
+
+				source = sourceCopy
+			}
+
+			if tryAssign(source, destination) {
+				return
+			}
+
+			if tryAssign(source.Elem(), destination.Elem()) {
+				return
+			}
+		}
+	} else {
+		if source.Kind() == reflect.Ptr {
+			if source.IsNil() {
+				return
+			}
+			source = source.Elem()
+		}
+
+		if tryAssign(source, destination) {
+			return
+		}
+	}
+
+	panic("jet: can't set " + source.Type().String() + " to " + destination.Type().String())
+}
+
+func createScanValue(columnTypes []*sql.ColumnType) []interface{} {
+	values := make([]interface{}, len(columnTypes))
+
+	for i, sqlColumnType := range columnTypes {
+		columnType := newScanType(sqlColumnType)
+
+		columnValue := reflect.New(columnType)
+
+		values[i] = columnValue.Interface()
+	}
+
+	return values
+}
+
+var boolType = reflect.TypeOf(true)
+var int8Type = reflect.TypeOf(int8(1))
+var unit8Type = reflect.TypeOf(uint8(1))
+var int16Type = reflect.TypeOf(int16(1))
+var uint16Type = reflect.TypeOf(uint16(1))
+var int32Type = reflect.TypeOf(int32(1))
+var uint32Type = reflect.TypeOf(uint32(1))
+var int64Type = reflect.TypeOf(int64(1))
+var uint64Type = reflect.TypeOf(uint64(1))
+
+var nullBoolType = reflect.TypeOf(sql.NullBool{})
+var nullInt8Type = reflect.TypeOf(internal.NullInt8{})
+var nullInt16Type = reflect.TypeOf(internal.NullInt16{})
+var nullInt32Type = reflect.TypeOf(internal.NullInt32{})
+var nullInt64Type = reflect.TypeOf(sql.NullInt64{})
+var nullFloat32Type = reflect.TypeOf(internal.NullFloat32{})
+var nullFloat64Type = reflect.TypeOf(sql.NullFloat64{})
+var nullStringType = reflect.TypeOf(sql.NullString{})
+var nullTimeType = reflect.TypeOf(internal.NullTime{})
+var nullByteArrayType = reflect.TypeOf(internal.NullByteArray{})
+
+func newScanType(columnType *sql.ColumnType) reflect.Type {
+
+	switch columnType.DatabaseTypeName() {
+	case "TINYINT":
+		return nullInt8Type
+	case "INT2", "SMALLINT", "YEAR":
+		return nullInt16Type
+	case "INT4", "MEDIUMINT", "INT":
+		return nullInt32Type
+	case "INT8", "BIGINT":
+		return nullInt64Type
+	case "CHAR", "VARCHAR", "TEXT", "", "_TEXT", "TSVECTOR", "BPCHAR", "UUID", "JSON", "JSONB", "INTERVAL", "POINT", "BIT", "VARBIT", "XML":
+		return nullStringType
+	case "FLOAT4":
+		return nullFloat32Type
+	case "FLOAT8", "NUMERIC", "DECIMAL", "FLOAT", "DOUBLE":
+		return nullFloat64Type
+	case "BOOL":
+		return nullBoolType
+	case "BYTEA", "BINARY", "VARBINARY", "BLOB":
+		return nullByteArrayType
+	case "DATE", "DATETIME", "TIMESTAMP", "TIMESTAMPTZ", "TIME", "TIMETZ":
+		return nullTimeType
+	default:
+		return nullStringType
+	}
+}
+
+func isPrimaryKey(field reflect.StructField, primaryKeyOverwrites []string) bool {
+	if len(primaryKeyOverwrites) > 0 {
+		return utils.StringSliceContains(primaryKeyOverwrites, field.Name)
+	}
+
+	sqlTag := field.Tag.Get("sql")
+
+	return sqlTag == "primary_key"
+}
+
+func parentFieldPrimaryKeyOverwrite(parentField *reflect.StructField) []string {
+	if parentField == nil {
+		return nil
+	}
+
+	sqlTag := parentField.Tag.Get("sql")
+
+	if !strings.HasPrefix(sqlTag, "primary_key") {
+		return nil
+	}
+
+	parts := strings.Split(sqlTag, "=")
+
+	if len(parts) < 2 {
+		return nil
+	}
+
+	return strings.Split(parts[1], ",")
+}
+
+func indirectType(reflectType reflect.Type) reflect.Type {
+	if reflectType.Kind() != reflect.Ptr {
+		return reflectType
+	}
+	return reflectType.Elem()
+}
+
+func fieldToString(field *reflect.StructField) string {
+	if field == nil {
+		return ""
+	}
+
+	return " at '" + field.Name + " " + field.Type.String() + "'"
+}

tests/mysql/alltypes_test.go

@@ -516,7 +516,8 @@ func TestStringOperators(t *testing.T) {
 
 	fmt.Println(query.DebugSql())
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 
 	assert.NilError(t, err)
 }
@@ -586,7 +587,8 @@ FROM test_sample.all_types;
 `, "20:34:58", "23:06:06", "22:06:06.011", "21:06:06.011111", "20:16:06",
 		"19:26:06", "18:36:06", "17:46:06", "16:56:56", "15:16:46", "14:26:36")
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 
 	assert.NilError(t, err)
 }
@@ -646,7 +648,8 @@ SELECT CAST(? AS DATE),
 FROM test_sample.all_types;
 `)
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 
 	assert.NilError(t, err)
 }
@@ -708,7 +711,8 @@ SELECT all_types.date_time = all_types.date_time,
 FROM test_sample.all_types;
 `)
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 
 	assert.NilError(t, err)
 }
@@ -769,7 +773,8 @@ SELECT all_types.timestamp = all_types.timestamp,
      CURRENT_TIMESTAMP(2)
 FROM test_sample.all_types;
 `)
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 
 	assert.NilError(t, err)
 }

tests/mysql/select_test.go

@@ -228,7 +228,8 @@ LIMIT ?;
 
 	testutils.AssertStatementSql(t, query, expectedSQL, int64(1), int64(1), int64(10), int64(1), int64(2), int64(1), int64(12))
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 	assert.NilError(t, err)
 }
 
@@ -263,7 +264,8 @@ LIMIT ?;
 
 	testutils.AssertStatementSql(t, query2, expectedSQL, int64(1), int64(10), int64(1), int64(2), int64(1))
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 	assert.NilError(t, err)
 }
 
@@ -305,7 +307,8 @@ OFFSET ?;
 
 	testutils.AssertStatementSql(t, query2, expectedSQL, int64(1), int64(10), int64(1), int64(2), int64(4), int64(3))
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 	assert.NilError(t, err)
 }
 
@@ -510,7 +513,8 @@ SELECT true,
      'date';
 `)
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 	assert.NilError(t, err)
 }
 
@@ -530,7 +534,8 @@ LOCK IN SHARE MODE;
 
 	testutils.AssertDebugStatementSql(t, query, expectedSQL)
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 	assert.NilError(t, err)
 }
 
@@ -606,7 +611,8 @@ GROUP BY payment.amount, payment.customer_id, payment.payment_date;
 
 	testutils.AssertStatementSql(t, query, expectedSQL, 100, 100, int64(10))
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 	assert.NilError(t, err)
 }
 
@@ -641,7 +647,8 @@ ORDER BY payment.customer_id;
 
 	testutils.AssertStatementSql(t, query, expectedSQL, int64(10))
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 
 	assert.NilError(t, err)
 }

tests/postgres/alltypes_test.go

@@ -134,7 +134,7 @@ LIMIT $5;
 func TestExpressionCast(t *testing.T) {
 
 	query := AllTypes.SELECT(
-		postgres.CAST(Int(150)).AS_CHAR(12),
+		postgres.CAST(Int(150)).AS_CHAR(12).AS("char12"),
 		postgres.CAST(String("TRUE")).AS_BOOL(),
 		postgres.CAST(String("111")).AS_SMALLINT(),
 		postgres.CAST(String("111")).AS_INTEGER(),
@@ -170,7 +170,8 @@ func TestExpressionCast(t *testing.T) {
 
 	//fmt.Println(query.DebugSql())
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 
 	assert.NilError(t, err)
 }
@@ -249,7 +250,8 @@ func TestStringOperators(t *testing.T) {
 
 	//fmt.Println(query.DebugSql())
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 
 	assert.NilError(t, err)
 }
@@ -618,7 +620,8 @@ func TestTimeExpression(t *testing.T) {
 
 	//fmt.Println(query.DebugSql())
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 
 	assert.NilError(t, err)
 }

tests/postgres/scan_test.go

@@ -1,6 +1,7 @@
 package postgres
 
 import (
+	"database/sql"
 	"fmt"
 	"github.com/go-jet/jet/internal/testutils"
 	. "github.com/go-jet/jet/postgres"
@@ -50,14 +51,16 @@ func TestScanToInvalidDestination(t *testing.T) {
 
 func TestScanToValidDestination(t *testing.T) {
 	t.Run("pointer to struct", func(t *testing.T) {
-		err := query.Query(db, &struct{}{})
+		dest := []struct{}{}
+		err := query.Query(db, &dest)
 
 		assert.NilError(t, err)
 	})
 
 	t.Run("global query function scan", func(t *testing.T) {
 		queryStr, args := query.Sql()
-		err := qrm.Query(nil, db, queryStr, args, &struct{}{})
+		dest := []struct{}{}
+		err := qrm.Query(nil, db, queryStr, args, &dest)
 		assert.NilError(t, err)
 	})
 
@@ -692,6 +695,35 @@ func TestScanToSlice(t *testing.T) {
 	})
 }
 
+func TestStructScanErrNoRows(t *testing.T) {
+	query := SELECT(Customer.AllColumns).
+		FROM(Customer).
+		WHERE(Customer.CustomerID.EQ(Int(-1)))
+
+	customer := model.Customer{}
+
+	err := query.Query(db, &customer)
+
+	assert.Error(t, err, sql.ErrNoRows.Error())
+}
+
+func TestStructScanAllNull(t *testing.T) {
+	query := SELECT(NULL.AS("null1"), NULL.AS("null2"))
+
+	dest := struct {
+		Null1 *int
+		Null2 *int
+	}{}
+
+	err := query.Query(db, &dest)
+
+	assert.NilError(t, err)
+	assert.DeepEqual(t, dest, struct {
+		Null1 *int
+		Null2 *int
+	}{})
+}
+
 var address256 = model.Address{
 	AddressID:  256,
 	Address:    "1497 Yuzhou Drive",

tests/postgres/select_test.go

@@ -162,7 +162,8 @@ LIMIT 12;
 
 	testutils.AssertDebugStatementSql(t, query, expectedSQL, int64(1), int64(1), int64(10), int64(1), int64(2), int64(1), int64(12))
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 	assert.NilError(t, err)
 }
 
@@ -1617,7 +1618,8 @@ SELECT true,
      'date';
 `)
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 	assert.NilError(t, err)
 }
 
@@ -1688,7 +1690,8 @@ GROUP BY payment.amount, payment.customer_id, payment.payment_date;
 
 	testutils.AssertStatementSql(t, query, expectedSQL, 100, 100, int64(10))
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 	assert.NilError(t, err)
 }
 
@@ -1723,12 +1726,14 @@ ORDER BY payment.customer_id;
 
 	testutils.AssertStatementSql(t, query, expectedSQL, int64(10))
 
-	err := query.Query(db, &struct{}{})
+	dest := []struct{}{}
+	err := query.Query(db, &dest)
 
 	assert.NilError(t, err)
 }
 
 func TestSimpleView(t *testing.T) {
+
 	query := SELECT(
 		view.ActorInfo.AllColumns,
 	).
@@ -1743,6 +1748,12 @@ func TestSimpleView(t *testing.T) {
 		FilmInfo  string
 	}
 
+	//sql, args := query.Sql()
+	//
+	//row := db.QueryRow(sql, args...)
+	//
+	//row.Scan()
+
 	var dest []ActorInfo
 
 	err := query.Query(db, &dest)