fix(database): 素材存储 - 扩容生成素材 ID 及关联字段

backend/internal/database/schema.go

@@ -1,6 +1,10 @@
 package database
 
 import (
+	"database/sql"
+	"errors"
+	"fmt"
+
 	"infinite-canvas/backend/internal/model"
 
 	"gorm.io/gorm"
@@ -71,6 +75,9 @@ func MigrateSchema(db *gorm.DB) error {
 			return err
 		}
 	}
+	if err := widenPostgresAssetIDColumns(db); err != nil {
+		return err
+	}
 	if err := db.AutoMigrate(Models()...); err != nil {
 		return err
 	}
@@ -83,3 +90,44 @@ func MigrateSchema(db *gorm.DB) error {
 	}
 	return db.Exec("CREATE UNIQUE INDEX IF NOT EXISTS idx_users_email_nonempty ON users(lower(email)) WHERE email <> ''").Error
 }
+
+type varcharColumnMigration struct {
+	table     string
+	column    string
+	statement string
+}
+
+var assetIDColumnMigrations = []varcharColumnMigration{
+	{table: "assets", column: "id", statement: `ALTER TABLE "assets" ALTER COLUMN "id" TYPE varchar(80)`},
+	{table: "project_asset_links", column: "asset_id", statement: `ALTER TABLE "project_asset_links" ALTER COLUMN "asset_id" TYPE varchar(80)`},
+	{table: "project_asset_candidates", column: "resolved_asset_id", statement: `ALTER TABLE "project_asset_candidates" ALTER COLUMN "resolved_asset_id" TYPE varchar(80)`},
+	{table: "asset_versions", column: "asset_id", statement: `ALTER TABLE "asset_versions" ALTER COLUMN "asset_id" TYPE varchar(80)`},
+}
+
+// PostgreSQL Migrator 跳过主键列变更，素材 ID 扩容必须在 AutoMigrate 前显式执行。
+func widenPostgresAssetIDColumns(db *gorm.DB) error {
+	if db.Dialector.Name() != "postgres" {
+		return nil
+	}
+	for _, migration := range assetIDColumnMigrations {
+		var currentLength sql.NullInt64
+		err := db.Raw(
+			"SELECT character_maximum_length FROM information_schema.columns WHERE table_schema = current_schema() AND table_name = ? AND column_name = ?",
+			migration.table,
+			migration.column,
+		).Row().Scan(&currentLength)
+		if errors.Is(err, sql.ErrNoRows) {
+			continue
+		}
+		if err != nil {
+			return fmt.Errorf("检查 PostgreSQL 素材 ID 列 %s.%s：%w", migration.table, migration.column, err)
+		}
+		if !currentLength.Valid || currentLength.Int64 >= model.AssetIDMaxLength {
+			continue
+		}
+		if err := db.Exec(migration.statement).Error; err != nil {
+			return fmt.Errorf("扩容 PostgreSQL 素材 ID 列 %s.%s：%w", migration.table, migration.column, err)
+		}
+	}
+	return nil
+}