Refactor nested preloading associations, close #3970

callbacks/preload.go

@@ -9,10 +9,9 @@ import (
 	"gorm.io/gorm/utils"
 )
 
-func preload(db *gorm.DB, rels []*schema.Relationship, conds []interface{}) {
+func preload(db *gorm.DB, rel *schema.Relationship, conds []interface{}, preloads map[string][]interface{}) {
 	var (
 		reflectValue     = db.Statement.ReflectValue
-		rel              = rels[len(rels)-1]
 		tx               = db.Session(&gorm.Session{NewDB: true}).Model(nil).Session(&gorm.Session{SkipHooks: db.Statement.SkipHooks})
 		relForeignKeys   []string
 		relForeignFields []*schema.Field
@@ -27,10 +26,6 @@ func preload(db *gorm.DB, rels []*schema.Relationship, conds []interface{}) {
 		return true
 	})
 
-	if len(rels) > 1 {
-		reflectValue = schema.GetRelationsValues(reflectValue, rels[:len(rels)-1])
-	}
-
 	if rel.JoinTable != nil {
 		var joinForeignFields, joinRelForeignFields []*schema.Field
 		var joinForeignKeys []string
@@ -97,6 +92,11 @@ func preload(db *gorm.DB, rels []*schema.Relationship, conds []interface{}) {
 		}
 	}
 
+	// nested preload
+	for p, pvs := range preloads {
+		tx = tx.Preload(p, pvs...)
+	}
+
 	reflectResults := rel.FieldSchema.MakeSlice().Elem()
 	column, values := schema.ToQueryValues(clause.CurrentTable, relForeignKeys, foreignValues)
 

callbacks/query.go

@@ -8,7 +8,6 @@ import (
 
 	"gorm.io/gorm"
 	"gorm.io/gorm/clause"
-	"gorm.io/gorm/schema"
 )
 
 func Query(db *gorm.DB) {
@@ -168,48 +167,37 @@ func BuildQuerySQL(db *gorm.DB) {
 
 func Preload(db *gorm.DB) {
 	if db.Error == nil && len(db.Statement.Preloads) > 0 {
-		preloadMap := map[string][]string{}
+		preloadMap := map[string]map[string][]interface{}{}
 		for name := range db.Statement.Preloads {
 			if name == clause.Associations {
 				for _, rel := range db.Statement.Schema.Relationships.Relations {
 					if rel.Schema == db.Statement.Schema {
-						preloadMap[rel.Name] = []string{rel.Name}
+						preloadMap[rel.Name] = nil
 					}
 				}
 			} else {
 				preloadFields := strings.Split(name, ".")
-				for idx := range preloadFields {
+				if _, ok := preloadMap[preloadFields[0]]; !ok {
-					preloadMap[strings.Join(preloadFields[:idx+1], ".")] = preloadFields[:idx+1]
+					preloadMap[preloadFields[0]] = map[string][]interface{}{}
+				}
+
+				if value := strings.TrimPrefix(strings.TrimPrefix(name, preloadFields[0]), "."); value != "" {
+					preloadMap[preloadFields[0]][value] = db.Statement.Preloads[name]
 				}
 			}
 		}
 
-		preloadNames := make([]string, len(preloadMap))
+		preloadNames := make([]string, 0, len(preloadMap))
-		idx := 0
 		for key := range preloadMap {
-			preloadNames[idx] = key
+			preloadNames = append(preloadNames, key)
-			idx++
 		}
 		sort.Strings(preloadNames)
 
 		for _, name := range preloadNames {
-			var (
+			if rel := db.Statement.Schema.Relationships.Relations[name]; rel != nil {
-				curSchema     = db.Statement.Schema
+				preload(db, rel, db.Statement.Preloads[name], preloadMap[name])
-				preloadFields = preloadMap[name]
-				rels          = make([]*schema.Relationship, len(preloadFields))
-			)
-
-			for idx, preloadField := range preloadFields {
-				if rel := curSchema.Relationships.Relations[preloadField]; rel != nil {
-					rels[idx] = rel
-					curSchema = rel.FieldSchema
 			} else {
-					db.AddError(fmt.Errorf("%v: %w", name, gorm.ErrUnsupportedRelation))
+				db.AddError(fmt.Errorf("%v: %w for schema %v", name, gorm.ErrUnsupportedRelation, db.Statement.Schema.Name))
-				}
-			}
-
-			if db.Error == nil {
-				preload(db, rels, db.Statement.Preloads[name])
 			}
 		}
 	}