Fix: Composite primary key with auto-increment value returns 0 after insert (#6127)

* Fix #4930 workaround for databases that support auto-increment in composite primary key.

* Add test for composite key with auto-increment.

* schema.go: use field.AutoIncrement instead of field.TagSettings["AUTOINCREMENT"], add test to check autoincrement:false

create_test.go: remove unused code: drop table CompositeKeyProduct

---------

Co-authored-by: Jinzhu <wosmvp@gmail.com>

schema/schema.go

@@ -221,8 +221,18 @@ func ParseWithSpecialTableName(dest interface{}, cacheStore *sync.Map, namer Nam
 		}
 	}
 
-	if schema.PrioritizedPrimaryField == nil && len(schema.PrimaryFields) == 1 {
+	if schema.PrioritizedPrimaryField == nil {
-		schema.PrioritizedPrimaryField = schema.PrimaryFields[0]
+		if len(schema.PrimaryFields) == 1 {
+			schema.PrioritizedPrimaryField = schema.PrimaryFields[0]
+		} else if len(schema.PrimaryFields) > 1 {
+			// If there are multiple primary keys, the AUTOINCREMENT field is prioritized
+			for _, field := range schema.PrimaryFields {
+				if field.AutoIncrement {
+					schema.PrioritizedPrimaryField = field
+					break
+				}
+			}
+		}
 	}
 
 	for _, field := range schema.PrimaryFields {

schema/schema_test.go

@@ -293,3 +293,44 @@ func TestEmbeddedStructForCustomizedNamingStrategy(t *testing.T) {
 		})
 	}
 }
+
+func TestCompositePrimaryKeyWithAutoIncrement(t *testing.T) {
+	type Product struct {
+		ProductID    uint `gorm:"primaryKey;autoIncrement"`
+		LanguageCode uint `gorm:"primaryKey"`
+		Code         string
+		Name         string
+	}
+	type ProductNonAutoIncrement struct {
+		ProductID    uint `gorm:"primaryKey;autoIncrement:false"`
+		LanguageCode uint `gorm:"primaryKey"`
+		Code         string
+		Name         string
+	}
+
+	product, err := schema.Parse(&Product{}, &sync.Map{}, schema.NamingStrategy{})
+	if err != nil {
+		t.Fatalf("failed to parse product struct with composite primary key, got error %v", err)
+	}
+
+	prioritizedPrimaryField := schema.Field{
+		Name: "ProductID", DBName: "product_id", BindNames: []string{"ProductID"}, DataType: schema.Uint, PrimaryKey: true, Size: 64, HasDefaultValue: true, AutoIncrement: true, TagSettings: map[string]string{"PRIMARYKEY": "PRIMARYKEY", "AUTOINCREMENT": "AUTOINCREMENT"},
+	}
+
+	product.Fields = []*schema.Field{product.PrioritizedPrimaryField}
+
+	checkSchemaField(t, product, &prioritizedPrimaryField, func(f *schema.Field) {
+		f.Creatable = true
+		f.Updatable = true
+		f.Readable = true
+	})
+
+	productNonAutoIncrement, err := schema.Parse(&ProductNonAutoIncrement{}, &sync.Map{}, schema.NamingStrategy{})
+	if err != nil {
+		t.Fatalf("failed to parse productNonAutoIncrement struct with composite primary key, got error %v", err)
+	}
+
+	if productNonAutoIncrement.PrioritizedPrimaryField != nil {
+		t.Fatalf("PrioritizedPrimaryField of non autoincrement composite key should be nil")
+	}
+}

tests/create_test.go

@@ -548,6 +548,35 @@ func TestFirstOrCreateRowsAffected(t *testing.T) {
 	}
 }
 
+func TestCreateWithAutoIncrementCompositeKey(t *testing.T) {
+	type CompositeKeyProduct struct {
+		ProductID    int `gorm:"primaryKey;autoIncrement:true;"` // primary key
+		LanguageCode int `gorm:"primaryKey;"`                    // primary key
+		Code         string
+		Name         string
+	}
+
+	if err := DB.AutoMigrate(&CompositeKeyProduct{}); err != nil {
+		t.Fatalf("failed to migrate, got error %v", err)
+	}
+
+	prod := &CompositeKeyProduct{
+		LanguageCode: 56,
+		Code:         "Code56",
+		Name:         "ProductName56",
+	}
+	if err := DB.Create(&prod).Error; err != nil {
+		t.Fatalf("failed to create, got error %v", err)
+	}
+
+	newProd := &CompositeKeyProduct{}
+	if err := DB.First(&newProd).Error; err != nil {
+		t.Fatalf("errors happened when query: %v", err)
+	} else {
+		AssertObjEqual(t, newProd, prod, "ProductID", "LanguageCode", "Code", "Name")
+	}
+}
+
 func TestCreateOnConfilctWithDefalutNull(t *testing.T) {
 	type OnConfilctUser struct {
 		ID     string