如何防止注入的DbContext被释放？遇ObjectDisposedException

我创建了ObjectBuilder类，通过构造函数注入dbContext并将其设为只读属性。类中包含多个使用dbContext的方法，比如CreateOrUpdateObject。在API控制器中实例化ObjectBuilder后，连续三次调用CreateOrUpdateObject方法：第一次执行正常，但第二次触发了ObjectDisposedException。我理解该异常含义，但未手动释放上下文或使用using语句，无法解决单次方法执行后上下文就被释放、后续方法无法运行的问题，恳请告知如何避免DbContext被释放以支持链式调用。

ObjectBuilder类代码片段 #

class ObjectBuilder
{
    readonly GuidObjectBuilder _guidObjectBuilder;
    readonly projectviewerContext _db;
    bool UpdatedGuidsArray { get; set; }
    int UpdatedObjectCount { get; set; }
    int CreatedObjectCount { get; set; }
    ProjectObjects ActiveObject { get; set; }

    public ObjectBuilder(GuidObjectBuilder guidObjectBuilder, projectviewerContext db)
    {
        this._guidObjectBuilder = guidObjectBuilder;
        this._db = db;
        this.UpdatedGuidsArray = false;
        this.UpdatedObjectCount = 0;
        this.CreatedObjectCount = 0;
    }

    public async Task<dynamic> CreateOrUpdateObject(string projectName, string tag, string pidClass, string guId, string fileName)
    {
        //SEND ONE ENTRY RETURNS A PROJECT_OBJECT MODEL
        if (this._db == null) throw new ArgumentNullException("The object builder class has not been set a database. Set the object with a database");
        try
        {
            //Check for an initial entry
            List<ProjectObjects> matchingProjectObjects = (from data in this._db.ProjectObjects.ToList()
                                                            where data.ProjectName == projectName &&
                                                            data.Tag == tag
                                                            select data).ToList();

            if (matchingProjectObjects.Any())
            {
                this.ActiveObject = this.UpdateProjectObject(matchingProjectObjects[0], pidClass, guId, fileName);
                this._db.Update(this.ActiveObject);
                this.UpdatedObjectCount++;
            }
            else
            {
                this.ActiveObject = this.CreateProjectObject(projectName, tag, pidClass, guId, fileName);
                this._db.Add(this.ActiveObject);
                this.CreatedObjectCount++;
            }
            await this._db.SaveChangesAsync();
            if (this.UpdatedGuidsArray)
            {
                //Add new guid
                await this._guidObjectBuilder.CreateOrUpdateUponModelOpen(this.ActiveObject.Id, guId, fileName);
            }
            this.UpdatedGuidsArray = false;
            return this.ActiveObject;
            
        }
        catch (System.Exception error)
        {
            return error;
        }
    }
}

测试端点代码片段 #

[HttpPost]
[Route("api/objectCreation/test1")]
public async Task<dynamic> TestOne()
{
    try
    {
        projectviewerContext db = new projectviewerContext();
        ObjectBuilder objectBuilder = new ObjectBuilder(new GuidObjectBuilder(db), db);
        await objectBuilder.CreateOrUpdateObject("Project 1", "VV00011", "Gate Valve", "XXCCBBVVNNDDFFHH", "3D_Model.nwd");
        await objectBuilder.CreateOrUpdateObject("Project 1", "VV00012", "Gate Valve", "XXFFGGHHIILLMMNN", "3D_Model.nwd");
        await objectBuilder.CreateOrUpdateObject("Project 1", "VV00014", "Gate Valve", "123456789", "PID_drawing.nwd");
        return "bang";
    }
    catch (System.Exception error)
    {
        return error.Message;
    }
}

问题原因及解决办法 #

核心原因 #

问题大概率出在GuidObjectBuilder内部：你将同一个dbContext实例传给了ObjectBuilder和GuidObjectBuilder，如果GuidObjectBuilder的CreateOrUpdateUponModelOpen方法里存在释放dbContext的逻辑（比如用using包裹传入的dbContext、手动调用db.Dispose()），就会导致后续调用时ObjectBuilder持有的dbContext已被销毁。

另外，手动实例化dbContext的方式不符合ASP.NET Core的生命周期管理规范，也容易引发此类问题。

解决步骤 #

1. 检查并修复GuidObjectBuilder的实现
   打开GuidObjectBuilder代码，确认CreateOrUpdateUponModelOpen方法中是否存在释放dbContext的逻辑：

   • 若有用using(var db = ...)包裹传入的dbContext，直接删除该结构
   • 若有调用db.Dispose()，立即移除该代码
     dbContext的生命周期应由外部（如依赖注入容器）统一管理，内部方法不应私自释放实例。

2. 改用依赖注入管理DbContext生命周期（推荐）
   放弃手动new dbContext，通过ASP.NET Core依赖注入容器统一管理对象生命周期：

   • 在Program.cs中注册DbContext：

     builder.Services.AddDbContext<projectviewerContext>(options =>
         options.UseSqlServer(builder.Configuration.GetConnectionString("YourConnectionString")));
     

   • 注册GuidObjectBuilder和ObjectBuilder为Scoped服务（与DbContext生命周期一致）：

     builder.Services.AddScoped<GuidObjectBuilder>();
     builder.Services.AddScoped<ObjectBuilder>();
     

   • 修改控制器，通过构造函数注入ObjectBuilder：

     private readonly ObjectBuilder _objectBuilder;
     
     public YourController(ObjectBuilder objectBuilder)
     {
         _objectBuilder = objectBuilder;
     }
     
     [HttpPost]
     [Route("api/objectCreation/test1")]
     public async Task<dynamic> TestOne()
     {
         try
         {
             await _objectBuilder.CreateOrUpdateObject("Project 1", "VV00011", "Gate Valve", "XXCCBBVVNNDDFFHH", "3D_Model.nwd");
             await _objectBuilder.CreateOrUpdateObject("Project 1", "VV00012", "Gate Valve", "XXFFGGHHIILLMMNN", "3D_Model.nwd");
             await _objectBuilder.CreateOrUpdateObject("Project 1", "VV00014", "Gate Valve", "123456789", "PID_drawing.nwd");
             return "bang";
         }
         catch (System.Exception error)
         {
             return error.Message;
         }
     }
     

   依赖注入容器会自动确保在整个请求周期内，dbContext实例不会被提前释放。

3. 临时应急方案（不推荐，仅用于快速验证）
   若暂时无法修改依赖注入逻辑，可在测试端点中用using包裹dbContext实例，确保所有调用完成后才回收：

   [HttpPost]
   [Route("api/objectCreation/test1")]
   public async Task<dynamic> TestOne()
   {
       try
       {
           using(var db = new projectviewerContext())
           {
               ObjectBuilder objectBuilder = new ObjectBuilder(new GuidObjectBuilder(db), db);
               await objectBuilder.CreateOrUpdateObject("Project 1", "VV00011", "Gate Valve", "XXCCBBVVNNDDFFHH", "3D_Model.nwd");
               await objectBuilder.CreateOrUpdateObject("Project 1", "VV00012", "Gate Valve", "XXFFGGHHIILLMMNN", "3D_Model.nwd");
               await objectBuilder.CreateOrUpdateObject("Project 1", "VV00014", "Gate Valve", "123456789", "PID_drawing.nwd");
           }
           return "bang";
       }
       catch (System.Exception error)
       {
           return error.Message;
       }
   }
   

内容的提问来源于stack exchange，提问作者SgDyl95