从DbSet返回没有错误的3表“不能从查询推断” [英] Returning from a DbSet 3 tables without the error "cannot be inferred from the query"

问题描述

我有3个班。锻炼锻炼，锻炼锻炼和锻炼。

我想使用将锻炼课程 与 WorkoutSession 有关。 WorkoutSession有很多的WorkoutSessionExercise，而且这些与练习中只有1到1个关系。

  var query = from workoutSession in DatabaseContext 。workOutable< WorkoutSession>（）
 from workoutSessionExercises in workoutSession.WorkoutSessionExercises 
 from exerciseInfo in workoutSessionExercises.Exercise 
 where workoutSession.Id == id 
 select workoutSession; 
  

最后一个FROM有错误：不能从查询推断类型参数。

如何使用Linq To Entity加载三层深层对象？

解决方案

这样的工作吗？

  DatabaseContext.SetOwnable< WorkoutSession> 
 .Include（WorkoutSessionExercises.Exercise）
 .Where（w => w.Id == id）; 
  

替代语法：

  from DatabaseContext.SetOwnable< WorkoutSession>中的workoutSession 
 .Include（WorkoutSessionExercises.Exercise）
其中workoutSession.Id == id 
 select workoutSession; 
  

这里的关键是 Include

修改

尝试这样来绕过基于字符串的包（从使用LINQ包括嵌套实体的灵感）：

  var query = from DatabaseContext.SetOwnable< WorkoutSession>中的workoutSession 
选择新
 {
 WorkoutSession，
 WorkoutSessionExercises =来自workoutSessionExercise 
 DatabaseContext.SetOwnable< WorkoutSessionExercises> 
选择新
 {
 WorkoutExercise =来自workoutExercise 
 DatabaseContext.SetOwnable< WorkoutExercise> 
选择workoutExercise 
} 
}; 
 
 var results = query.Select（r => r.WorkoutSession）.Where（w => w.Id == id）; 
  

I have 3 classes. WorkoutSession, WorkoutSessionExercise and Exercise.

I would like to return the WorkoutSession with its list of WorkoutSession with the Exercise related. WorkoutSession has many WorkoutSessionExercise, and these one has only a single 1 to 1 relationship with Exercise.

             var query = from workoutSession in DatabaseContext.SetOwnable<WorkoutSession>()
             from workoutSessionExercises in workoutSession.WorkoutSessionExercises
             from exerciseInfo in workoutSessionExercises.Exercise
             where workoutSession.Id == id
             select workoutSession;

The last FROM has the error : The type argument cannot be inferred from the query.

How can I load this three level deep objects with Linq To Entity?

解决方案

Would something like this work?

DatabaseContext.SetOwnable<WorkoutSession>
    .Include("WorkoutSessionExercises.Exercise")
    .Where(w => w.Id == id);

Alternate syntax:

from workoutSession in DatabaseContext.SetOwnable<WorkoutSession>
    .Include("WorkoutSessionExercises.Exercise")
    where workoutSession.Id == id
    select workoutSession;

The key here is that Include method - this allows you to indicate which related objects should be hydrated.

Edit

Try this to get around the string-based includes (inspiration from Include nested entities using LINQ):

var query = from workoutSession in DatabaseContext.SetOwnable<WorkoutSession>
select new
{
     WorkoutSession,
     WorkoutSessionExercises = from workoutSessionExercise in
        DatabaseContext.SetOwnable<WorkoutSessionExercises>
        select new
        {
            WorkoutExercise = from workoutExercise in
                DatabaseContext.SetOwnable<WorkoutExercise>
                select workoutExercise
        }
};

var results = query.Select(r => r.WorkoutSession).Where(w => w.Id == id);

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