EF 核心分组不适用于相关模型

Question

我是实体框架的新手。我可以设法创建表和工作 CRUD 操作。

我的模型如下

public class Break
    {
        [JsonProperty("id")]
        public int Id { get; set; }
        [JsonProperty("name")]
        public string Name { get; set; }
        [JsonProperty("duration")]
        public int Duration { get; set; }
        [JsonProperty("countable")]
        public bool Countable { get; set; }
    }

    public class BreakState
    {
        [JsonProperty("id")]
        public int Id { get; set; }
        [JsonProperty("level")]
        public int Level { get; set; }
        [JsonProperty("name")]
        public string Name { get; set; }
        [JsonProperty("isSupervisor")]
        public bool IsSupervisor { get; set; }
        [JsonProperty("isActive")]
        public bool IsActive { get; set; }
    }

    public class BreakRequest : BaseModel
    {
        [JsonProperty("dn")]
        public string DN { get; set; }
        [JsonProperty("agent")]
        public string Agent { get; set; }
        
        [JsonProperty("break")]
        public Break Break { get; set; }

        [JsonProperty("steps")]
        public List<BreakStep> Steps { get; set; }
    }

    public class BreakStep : BaseModel
    {
        [JsonProperty("state")]
        public BreakState BreakState { get; set; }
        [JsonProperty("note")]
        public string Note { get; set; }


        [JsonProperty("request_id")]
        public int BreakRequestId { get; set; }
        [JsonIgnore]
        public BreakRequest BreakRequest { get; set; }
    }

现在我需要从上下文中获取复杂的数据。

public int GetUsedBreak(string agent) {
            int sum_breaks_used = 0;
            var shift = GetShift(agent);
            if (shift != null) {
                using (var dbBreak = new BreakTimeDbContext())
                {
                    var breaks_countable = dbBreak.BreakRequests
                        .Where(x => x.DN == agent && x.Break.Countable && x.Steps.Count == 4 && x.CreatedAt > shift.Start)
                        .Select(x => x.Id).ToArray();
                    if (breaks_countable.Length > 0) {
                        sum_breaks_used = dbBreak.BreakSteps
                            .Include(i => i.BreakState)
                            .Where(w => breaks_countable.Contains(w.BreakRequestId))
                            .GroupBy(x => x.BreakRequestId)
                            .Select(g => new {
                                BreakId = g.Key,
                                Level3Time = g.Where(w => w.BreakState.Level == 3).First().CreatedAt,
                                Level4Time = g.Where(w => w.BreakState.Level == 4).First().CreatedAt
                            })
                            .Sum(x => ( x.Level4Time - x.Level3Time ).Minutes);
                    }
                }
            }
            return sum_breaks_used;
        }

通过这个函数，我尝试获得日期差异的总和。 但我收到以下错误

执行请求时发生未处理的异常。 System.InvalidOperationException：LINQ 表达式 'GroupByShaperExpression： KeySelector：b.BreakRequestId， 元素选择器：EntityShaper表达式： 实体类型：BreakStep 值缓冲区表达式： ProjectionBindingExpression：EmptyProjectionMember 可空：假

 .Where(w => w.BreakState.Level == 3)' 无法翻译。要么以可翻译的形式重写查询，

或者通过插入调用显式切换到客户端评估 “AsEnumerable”、“AsAsyncEnumerable”、“ToList”或“ToListAsync”。看 https://go.microsoft.com/fwlink/?linkid=2101038更多信息。

我只需要 4 级和 3 级差异。

我怎样才能用linq实现它？

注：问题标题可能不清楚，可以更改