change the method of initializing slice (#4097)

* change the method of initializing slice and fixed the length to be specified as 0

* keep the association.go code in the var group

* keep the association.go code in the var group

* change to initializing in var group

callbacks/associations.go

@@ -39,7 +39,7 @@ func SaveBeforeAssociations(create bool) func(db *gorm.DB) {
 				switch db.Statement.ReflectValue.Kind() {
 				case reflect.Slice, reflect.Array:
 					var (
-						objs      []reflect.Value
+						objs      = make([]reflect.Value, 0, db.Statement.ReflectValue.Len())
 						fieldType = rel.Field.FieldType
 						isPtr     = fieldType.Kind() == reflect.Ptr
 					)
@@ -140,7 +140,7 @@ func SaveAfterAssociations(create bool) func(db *gorm.DB) {
 					}
 
 					if elems.Len() > 0 {
-						assignmentColumns := []string{}
+						assignmentColumns := make([]string, 0, len(rel.References))
 						for _, ref := range rel.References {
 							assignmentColumns = append(assignmentColumns, ref.ForeignKey.DBName)
 						}
@@ -154,7 +154,7 @@ func SaveAfterAssociations(create bool) func(db *gorm.DB) {
 							f = f.Addr()
 						}
 
-						assignmentColumns := []string{}
+						assignmentColumns := make([]string, 0, len(rel.References))
 						for _, ref := range rel.References {
 							if ref.OwnPrimaryKey {
 								fv, _ := ref.PrimaryKey.ValueOf(db.Statement.ReflectValue)
@@ -219,7 +219,7 @@ func SaveAfterAssociations(create bool) func(db *gorm.DB) {
 				}
 
 				if elems.Len() > 0 {
-					assignmentColumns := []string{}
+					assignmentColumns := make([]string, 0, len(rel.References))
 					for _, ref := range rel.References {
 						assignmentColumns = append(assignmentColumns, ref.ForeignKey.DBName)
 					}
@@ -324,7 +324,7 @@ func onConflictOption(stmt *gorm.Statement, s *schema.Schema, selectColumns map[
 	}
 
 	if len(defaultUpdatingColumns) > 0 {
-		var columns []clause.Column
+		columns := make([]clause.Column, 0, len(s.PrimaryFieldDBNames))
 		for _, dbName := range s.PrimaryFieldDBNames {
 			columns = append(columns, clause.Column{Name: dbName})
 		}

callbacks/delete.go

@@ -41,7 +41,7 @@ func DeleteBeforeAssociations(db *gorm.DB) {
 							}
 
 							if len(db.Statement.Selects) > 0 {
-								var selects []string
+								selects := make([]string, 0, len(db.Statement.Selects))
 								for _, s := range db.Statement.Selects {
 									if s == clause.Associations {
 										selects = append(selects, s)
@@ -69,9 +69,9 @@ func DeleteBeforeAssociations(db *gorm.DB) {
 							}
 						case schema.Many2Many:
 							var (
-								queryConds     []clause.Expression
-								foreignFields  []*schema.Field
-								relForeignKeys []string
+								queryConds     = make([]clause.Expression, 0, len(rel.References))
+								foreignFields  = make([]*schema.Field, 0, len(rel.References))
+								relForeignKeys = make([]string, 0, len(rel.References))
 								modelValue     = reflect.New(rel.JoinTable.ModelType).Interface()
 								table          = rel.JoinTable.Table
 								tx             = db.Session(&gorm.Session{NewDB: true}).Model(modelValue).Table(table)

callbacks/preload.go

@@ -27,8 +27,13 @@ func preload(db *gorm.DB, rel *schema.Relationship, conds []interface{}, preload
 	})
 
 	if rel.JoinTable != nil {
-		var joinForeignFields, joinRelForeignFields []*schema.Field
-		var joinForeignKeys []string
+
+		var (
+			joinForeignFields    = make([]*schema.Field, 0, len(rel.References))
+			joinRelForeignFields = make([]*schema.Field, 0, len(rel.References))
+			joinForeignKeys      = make([]string, 0, len(rel.References))
+		)
+
 		for _, ref := range rel.References {
 			if ref.OwnPrimaryKey {
 				joinForeignKeys = append(joinForeignKeys, ref.ForeignKey.DBName)

schema/naming.go

@@ -92,7 +92,7 @@ var (
 )
 
 func init() {
-	var commonInitialismsForReplacer []string
+	commonInitialismsForReplacer := make([]string, 0, len(commonInitialisms))
 	for _, initialism := range commonInitialisms {
 		commonInitialismsForReplacer = append(commonInitialismsForReplacer, initialism, strings.Title(strings.ToLower(initialism)))
 	}