fix empty QueryClauses in association (#5502) (#5503)

* fix empty QueryClauses in association (#5502)

* test: empty QueryClauses in association (#5502)

* style: empty QueryClauses in association (#5502)

* style: empty QueryClauses in association (#5502)

association.go

@@ -507,7 +507,9 @@ func (association *Association) buildCondition() *DB {
 				joinStmt.AddClause(queryClause)
 			}
 			joinStmt.Build("WHERE")
-			tx.Clauses(clause.Expr{SQL: strings.Replace(joinStmt.SQL.String(), "WHERE ", "", 1), Vars: joinStmt.Vars})
+			if len(joinStmt.SQL.String()) > 0 {
+				tx.Clauses(clause.Expr{SQL: strings.Replace(joinStmt.SQL.String(), "WHERE ", "", 1), Vars: joinStmt.Vars})
+			}
 		}
 
 		tx = tx.Session(&Session{QueryFields: true}).Clauses(clause.From{Joins: []clause.Join{{

tests/associations_test.go

@@ -4,6 +4,8 @@ import (
 	"testing"
 
 	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+	"gorm.io/gorm/schema"
 	. "gorm.io/gorm/utils/tests"
 )
 
@@ -284,3 +286,65 @@ func TestAssociationError(t *testing.T) {
 	err = DB.Model(&emptyUser).Association("Languages").Delete(&user1.Languages)
 	AssertEqual(t, err, gorm.ErrPrimaryKeyRequired)
 }
+
+type (
+	myType           string
+	emptyQueryClause struct {
+		Field *schema.Field
+	}
+)
+
+func (myType) QueryClauses(f *schema.Field) []clause.Interface {
+	return []clause.Interface{emptyQueryClause{Field: f}}
+}
+
+func (sd emptyQueryClause) Name() string {
+	return "empty"
+}
+
+func (sd emptyQueryClause) Build(clause.Builder) {
+}
+
+func (sd emptyQueryClause) MergeClause(*clause.Clause) {
+}
+
+func (sd emptyQueryClause) ModifyStatement(stmt *gorm.Statement) {
+	// do nothing
+}
+
+func TestAssociationEmptyQueryClause(t *testing.T) {
+	type Organization struct {
+		gorm.Model
+		Name string
+	}
+	type Region struct {
+		gorm.Model
+		Name          string
+		Organizations []Organization `gorm:"many2many:region_orgs;"`
+	}
+	type RegionOrg struct {
+		RegionId       uint
+		OrganizationId uint
+		Empty          myType
+	}
+	if err := DB.SetupJoinTable(&Region{}, "Organizations", &RegionOrg{}); err != nil {
+		t.Fatalf("Failed to set up join table, got error: %s", err)
+	}
+	if err := DB.Migrator().DropTable(&Organization{}, &Region{}); err != nil {
+		t.Fatalf("Failed to migrate, got error: %s", err)
+	}
+	if err := DB.AutoMigrate(&Organization{}, &Region{}); err != nil {
+		t.Fatalf("Failed to migrate, got error: %v", err)
+	}
+	region := &Region{Name: "Region1"}
+	if err := DB.Create(region).Error; err != nil {
+		t.Fatalf("fail to create region %v", err)
+	}
+	var orgs []Organization
+
+	if err := DB.Model(&Region{}).Association("Organizations").Find(&orgs); err != nil {
+		t.Fatalf("fail to find region organizations %v", err)
+	} else {
+		AssertEqual(t, len(orgs), 0)
+	}
+}