diff --git a/backend/internal/logic/projects/handlers_test.go b/backend/internal/logic/projects/handlers_test.go
index 0120da4..2dc6785 100644
--- a/backend/internal/logic/projects/handlers_test.go
+++ b/backend/internal/logic/projects/handlers_test.go
@@ -142,6 +142,38 @@ func TestUpdateProject(t *testing.T) {
 		require.Equal(t, "更新后的项目说明", updated.Description)
 	})
 
+	t.Run("clears optional metadata while preserving omitted name and identifier", func(t *testing.T) {
+		router, project, _ := newProjectsHandlerTestRouter(t)
+		require.NoError(t, models.DBService.Model(project).Updates(map[string]any{
+			"icon":        "tree",
+			"background":  "#165DFF",
+			"description": "原项目说明",
+		}).Error)
+		originalName := project.Name
+		originalIdentifier := project.Identifier
+		body, err := json.Marshal(gin.H{
+			"icon":        "",
+			"background":  "",
+			"description": "",
+		})
+		require.NoError(t, err)
+		req := httptest.NewRequest(http.MethodPatch, "/api/v1/projects/"+project.Identity, bytes.NewReader(body))
+		req.Header.Set("Content-Type", "application/json")
+		req.Header.Set("Authorization", "Bearer test-token")
+		rec := httptest.NewRecorder()
+
+		router.ServeHTTP(rec, req)
+
+		require.Equal(t, http.StatusNoContent, rec.Code)
+		var updated models.SenlinAgentProject
+		require.NoError(t, models.DBService.First(&updated, project.ID).Error)
+		require.Equal(t, originalName, updated.Name)
+		require.Equal(t, originalIdentifier, updated.Identifier)
+		require.Empty(t, updated.Icon)
+		require.Empty(t, updated.Background)
+		require.Empty(t, updated.Description)
+	})
+
 	t.Run("returns not found when the identity is not owned by the current user", func(t *testing.T) {
 		router, _, _ := newProjectsHandlerTestRouter(t)
 		other, err := NewService().CreateProject(2, "Other", "")
diff --git a/backend/internal/logic/projects/service.go b/backend/internal/logic/projects/service.go
index 60f2182..170c1e1 100644
--- a/backend/internal/logic/projects/service.go
+++ b/backend/internal/logic/projects/service.go
@@ -151,15 +151,6 @@ func (s *Service) CreateProjectWithInput(ownerID uint, input CreateProjectReques
 	if identifier == "" {
 		identifier = projectInitials(name)
 	}
-	var count int64
-	if err := models.DBService.Model(&models.SenlinAgentProject{}).
-		Where("owner_id = ? AND identifier = ?", ownerID, identifier).
-		Count(&count).Error; err != nil {
-		return nil, err
-	}
-	if count > 0 {
-		return nil, ErrProjectIdentifierConflict
-	}
 	project := &models.SenlinAgentProject{
 		OwnerID:     ownerID,
 		Name:        name,
@@ -168,7 +159,10 @@ func (s *Service) CreateProjectWithInput(ownerID uint, input CreateProjectReques
 		Background:  strings.TrimSpace(input.Background),
 		Description: strings.TrimSpace(input.Description),
 	}
-	return project, models.DBService.Create(project).Error
+	if err := projectWriteError(models.DBService.Create(project).Error); err != nil {
+		return nil, err
+	}
+	return project, nil
 }
 
 // ListProjects 只返回当前所有者的公开 DTO，不让 handler 接触或序列化数据库模型。
@@ -199,6 +193,14 @@ var (
 	ErrProjectIdentifierConflict = errors.New("project identifier already exists")
 )
 
+// projectWriteError 将 Postgres/SQLite 经 Gorm 翻译后的唯一约束错误收敛为稳定业务冲突。
+func projectWriteError(err error) error {
+	if errors.Is(err, gorm.ErrDuplicatedKey) {
+		return ErrProjectIdentifierConflict
+	}
+	return err
+}
+
 // UpdateProject 仅更新项目设置白名单字段，查询和冲突检查均限定在当前所有者内。
 func (s *Service) UpdateProject(ownerID uint, identity string, input UpdateProjectRequest) error {
 	project, err := FindOwnedProject(ownerID, identity)
@@ -219,15 +221,6 @@ func (s *Service) UpdateProject(ownerID uint, identity string, input UpdateProje
 		if identifier == "" {
 			return ErrProjectIdentifierRequired
 		}
-		var count int64
-		if err := models.DBService.Model(&models.SenlinAgentProject{}).
-			Where("owner_id = ? AND identifier = ? AND id <> ?", ownerID, identifier, project.ID).
-			Count(&count).Error; err != nil {
-			return err
-		}
-		if count > 0 {
-			return ErrProjectIdentifierConflict
-		}
 		updates["identifier"] = identifier
 	}
 	if input.Icon != nil {
@@ -242,7 +235,7 @@ func (s *Service) UpdateProject(ownerID uint, identity string, input UpdateProje
 	if len(updates) == 0 {
 		return nil
 	}
-	return models.DBService.Model(project).Updates(updates).Error
+	return projectWriteError(models.DBService.Model(project).Updates(updates).Error)
 }
 
 func (s *Service) CreateTask(ownerID uint, projectID uint, input CreateTaskInput) (*models.SenlinAgentTask, error) {
diff --git a/backend/internal/logic/projects/service_test.go b/backend/internal/logic/projects/service_test.go
index 891c55f..1c322de 100644
--- a/backend/internal/logic/projects/service_test.go
+++ b/backend/internal/logic/projects/service_test.go
@@ -7,7 +7,9 @@ import (
 	"time"
 
 	"github.com/glebarez/sqlite"
+	"github.com/jackc/pgx/v5/pgconn"
 	"github.com/stretchr/testify/require"
+	"gorm.io/driver/postgres"
 	"gorm.io/gorm"
 	"senlinai-agent/backend/internal/models"
 )
@@ -29,6 +31,35 @@ func TestFindOwnedProjectScopesIdentityByOwner(t *testing.T) {
 	require.True(t, errors.Is(err, gorm.ErrRecordNotFound))
 }
 
+func TestProjectIdentifierDatabaseConstraintIsScopedByOwner(t *testing.T) {
+	database := newTestDB(t)
+	first := models.SenlinAgentProject{OwnerID: 1, Name: "Alpha", Identifier: "SHARED"}
+	require.NoError(t, database.Create(&first).Error)
+
+	duplicate := models.SenlinAgentProject{OwnerID: 1, Name: "Duplicate", Identifier: "SHARED"}
+	require.ErrorIs(t, database.Create(&duplicate).Error, gorm.ErrDuplicatedKey)
+
+	otherOwner := models.SenlinAgentProject{OwnerID: 2, Name: "Allowed", Identifier: "SHARED"}
+	require.NoError(t, database.Create(&otherOwner).Error)
+}
+
+func TestProjectIdentifierDatabaseErrorMapsToConflict(t *testing.T) {
+	database := newTestDB(t)
+	first := models.SenlinAgentProject{OwnerID: 1, Name: "Alpha", Identifier: "SHARED"}
+	require.NoError(t, database.Create(&first).Error)
+	duplicate := models.SenlinAgentProject{OwnerID: 1, Name: "Duplicate", Identifier: "SHARED"}
+	databaseErr := database.Create(&duplicate).Error
+	require.ErrorIs(t, databaseErr, gorm.ErrDuplicatedKey)
+
+	require.ErrorIs(t, projectWriteError(databaseErr), ErrProjectIdentifierConflict)
+}
+
+func TestPostgresDuplicateKeyErrorMapsToProjectConflict(t *testing.T) {
+	databaseErr := postgres.Dialector{}.Translate(&pgconn.PgError{Code: "23505"})
+	require.ErrorIs(t, databaseErr, gorm.ErrDuplicatedKey)
+	require.ErrorIs(t, projectWriteError(databaseErr), ErrProjectIdentifierConflict)
+}
+
 func TestProjectTagsAreScopedToProject(t *testing.T) {
 	newTestDB(t)
 	service := NewService()
@@ -318,7 +349,7 @@ func TestCreateCronPlanAddsPlanToOwnedProject(t *testing.T) {
 
 func newTestDB(t *testing.T) *gorm.DB {
 	t.Helper()
-	database, err := gorm.Open(sqlite.Open(fmt.Sprintf("file:%s?mode=memory&cache=shared", t.Name())), &gorm.Config{})
+	database, err := gorm.Open(sqlite.Open(fmt.Sprintf("file:%s?mode=memory&cache=shared", t.Name())), &gorm.Config{TranslateError: true})
 	require.NoError(t, err)
 	require.NoError(t, models.AutoMigrate(database))
 	models.DBService = database
diff --git a/backend/internal/models/new.go b/backend/internal/models/new.go
index 74b6ba4..4d9752d 100644
--- a/backend/internal/models/new.go
+++ b/backend/internal/models/new.go
@@ -8,7 +8,8 @@ import (
 var DBService *gorm.DB
 
 func New(dsn string) error {
-	db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{})
+	// 启用 Gorm 跨驱动错误翻译，业务层无需解析 Postgres 错误文本或 SQLSTATE。
+	db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{TranslateError: true})
 	if err != nil {
 		return err
 	}
diff --git a/backend/internal/models/project.go b/backend/internal/models/project.go
index 80cffea..f76e169 100644
--- a/backend/internal/models/project.go
+++ b/backend/internal/models/project.go
@@ -5,10 +5,10 @@ import "time"
 type SenlinAgentProject struct {
 	ID            uint   `gorm:"primaryKey"`
 	Identity      string `gorm:"type:char(36);uniqueIndex"`
-	OwnerID       uint   `gorm:"index;not null"`
+	OwnerID       uint   `gorm:"index;not null;uniqueIndex:uidx_senlin_agent_projects_owner_identifier,priority:1"`
 	OwnerIdentity string `gorm:"type:char(36);index"`
 	Name          string `gorm:"not null"`
-	Identifier    string `gorm:"index"`
+	Identifier    string `gorm:"index;uniqueIndex:uidx_senlin_agent_projects_owner_identifier,priority:2"`
 	Icon          string
 	Background    string
 	Description   string
diff --git a/backend/internal/seed/demo.go b/backend/internal/seed/demo.go
index 784f1cc..fecfc2e 100644
--- a/backend/internal/seed/demo.go
+++ b/backend/internal/seed/demo.go
@@ -77,17 +77,18 @@ func upsertUser(tx *gorm.DB, email string, displayName string, password string)
 func seedProjects(tx *gorm.DB, ownerID uint) ([]models.SenlinAgentProject, error) {
 	definitions := []struct {
 		Name        string
+		Identifier  string
 		Description string
 	}{
-		{Name: "项目 A1", Description: "企业智能协作平台的核心工作空间"},
-		{Name: "项目 A2", Description: "客户成功与交付跟踪"},
-		{Name: "数据中台", Description: "内部数据治理与指标分析"},
-		{Name: "运营自动化", Description: "定时任务和业务流程自动化"},
+		{Name: "项目 A1", Identifier: "A1", Description: "企业智能协作平台的核心工作空间"},
+		{Name: "项目 A2", Identifier: "A2", Description: "客户成功与交付跟踪"},
+		{Name: "数据中台", Identifier: "DATA", Description: "内部数据治理与指标分析"},
+		{Name: "运营自动化", Identifier: "AUTO", Description: "定时任务和业务流程自动化"},
 	}
 
 	projects := make([]models.SenlinAgentProject, 0, len(definitions))
 	for _, definition := range definitions {
-		project, err := firstOrCreateProject(tx, ownerID, definition.Name, definition.Description)
+		project, err := firstOrCreateProject(tx, ownerID, definition.Name, definition.Identifier, definition.Description)
 		if err != nil {
 			return nil, err
 		}
@@ -107,7 +108,7 @@ func seedProjects(tx *gorm.DB, ownerID uint) ([]models.SenlinAgentProject, error
 	return projects, nil
 }
 
-func firstOrCreateProject(tx *gorm.DB, ownerID uint, name string, description string) (models.SenlinAgentProject, error) {
+func firstOrCreateProject(tx *gorm.DB, ownerID uint, name string, identifier string, description string) (models.SenlinAgentProject, error) {
 	var project models.SenlinAgentProject
 	err := tx.Where("owner_id = ? AND name = ?", ownerID, name).First(&project).Error
 	if err == nil {
@@ -116,7 +117,7 @@ func firstOrCreateProject(tx *gorm.DB, ownerID uint, name string, description st
 	if err != gorm.ErrRecordNotFound {
 		return project, err
 	}
-	project = models.SenlinAgentProject{OwnerID: ownerID, Name: name, Description: description}
+	project = models.SenlinAgentProject{OwnerID: ownerID, Name: name, Identifier: identifier, Description: description}
 	return project, tx.Create(&project).Error
 }