First try for the Preload feature

README.md

@@ -1092,8 +1092,9 @@ db.Where("email = ?", "x@example.org").Attrs(User{RegisteredIp: "111.111.111.111
   db.Mode(&User{}).Do("EditForm").Get("edit_form_html")
   DefaultTimeZone, R/W Splitting, Validation
 * Github Pages
-* Includes
 * AlertColumn, DropColumn
+* db.Preload("Addresses.Map", "active = ?", true).Preload("Profile").Find(&users)
+* db.Find(&users).Related(&users)
 
 # Author
 

callback_query.go

@@ -3,6 +3,8 @@ package gorm
 import (
 	"fmt"
 	"reflect"
+
+	"github.com/jinzhu/gorm"
 )
 
 func Query(scope *Scope) {
@@ -13,6 +15,7 @@ func Query(scope *Scope) {
 		isPtr          bool
 		anyRecordFound bool
 		destType       reflect.Type
+		primaryKeys    []interface{}
 	)
 
 	var dest = scope.IndirectValue()
@@ -47,8 +50,9 @@ func Query(scope *Scope) {
 			return
 		}
 
-		columns, _ := rows.Columns()
+		preloadMap := map[string]map[string]*gorm.Field{}
 
+		columns, _ := rows.Columns()
 		defer rows.Close()
 		for rows.Next() {
 			scope.db.RowsAffected += 1
@@ -62,6 +66,7 @@ func Query(scope *Scope) {
 			var values = make([]interface{}, len(columns))
 
 			fields := scope.New(elem.Addr().Interface()).Fields()
+			var primaryKey interface{}
 			for index, column := range columns {
 				if field, ok := fields[column]; ok {
 					if field.Field.Kind() == reflect.Ptr {
@@ -69,6 +74,10 @@ func Query(scope *Scope) {
 					} else {
 						values[index] = reflect.New(reflect.PtrTo(field.Field.Type())).Interface()
 					}
+					if field.IsPrimaryKey {
+						primaryKey = values[index]
+						primaryKeys = append(primaryKeys, primaryKey)
+					}
 				} else {
 					var value interface{}
 					values[index] = &value
@@ -95,6 +104,34 @@ func Query(scope *Scope) {
 					dest.Set(reflect.Append(dest, elem))
 				}
 			}
+
+			if scope.Search.Preload != nil {
+				for key := range scope.Search.Preload {
+					if field := fields[key]; field != nil {
+						if preloadMap[key] == nil {
+							preloadMap[key] = map[string]reflect.Value{}
+						}
+						preloadMap[key][fmt.Sprintf("%v", primaryKey)] = field
+					}
+				}
+			}
+		}
+
+		for _, value := range preloadMap {
+			var typ reflect.Type
+			var relation *Relation
+			for _, v := range value {
+				typ = v.Field.Type()
+				relation = v.Relationship
+				break
+			}
+			sliceType := reflect.SliceOf(typ)
+			slice := reflect.MakeSlice(sliceType, 0, 0)
+			slicePtr := reflect.New(sliceType)
+			slicePtr.Elem().Set(slice)
+			if relation == "has_many" {
+				scope.NewDB().Find(slicePtr.Interface(), primaryKeys)
+			}
 		}
 
 		if !anyRecordFound && !isSlice {

main.go

@@ -156,10 +156,6 @@ func (s *DB) Joins(query string) *DB {
 	return s.clone().search.joins(query).db
 }
 
-func (s *DB) Includes(value interface{}) *DB {
-	return s.clone().search.includes(value).db
-}
-
 func (s *DB) Scopes(funcs ...func(*DB) *DB) *DB {
 	c := s
 	for _, f := range funcs {
@@ -432,6 +428,10 @@ func (s *DB) Association(column string) *Association {
 	return &Association{Scope: scope, Column: column, Error: s.Error, PrimaryKey: primaryKey, PrimaryType: primaryType, Field: field}
 }
 
+func (s *DB) Preload(column string, conditions ...interface{}) *DB {
+	return s.clone().search.preload(column, conditions...).db
+}
+
 // Set set value by name
 func (s *DB) Set(name string, value interface{}) *DB {
 	return s.clone().InstantSet(name, value)

search.go

@@ -13,6 +13,7 @@ type search struct {
 	Orders          []string
 	Joins           string
 	Selects         []map[string]interface{}
+	Preload         map[string][]interface{}
 	Offset          string
 	Limit           string
 	Group           string
@@ -23,6 +24,7 @@ type search struct {
 
 func (s *search) clone() *search {
 	return &search{
+		Preload:         s.Preload,
 		WhereConditions: s.WhereConditions,
 		OrConditions:    s.OrConditions,
 		NotConditions:   s.NotConditions,
@@ -100,12 +102,16 @@ func (s *search) having(query string, values ...interface{}) *search {
 	return s
 }
 
-func (s *search) includes(value interface{}) *search {
+func (s *search) joins(query string) *search {
+	s.Joins = query
 	return s
 }
 
-func (s *search) joins(query string) *search {
+func (s *search) preload(column string, values ...interface{}) *search {
-	s.Joins = query
+	if s.Preload == nil {
+		s.Preload = map[string][]interface{}{}
+	}
+	s.Preload[column] = values
 	return s
 }