从DbSet 3表返回无错误“不能从查询中推断". [英] Returning from a DbSet 3 tables without the error "cannot be inferred from the query"

问题描述

我有3个班级.WorkoutSession，WorkoutSessionExercise和锻炼.

I have 3 classes. WorkoutSession, WorkoutSessionExercise and Exercise.

我想返回WorkoutSession with 与Workout相关的WorkoutSession with 列表.WorkoutSession 有很多 WorkoutSessionExercise，而这一个与锻炼只有一对一的关系.

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;

最后一个FROM出现错误:无法从查询中推断出type参数.

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

如何使用Linq To Entity加载这三层深的对象?

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

推荐答案

这样的作品行吗?

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

备用语法:

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

这里的关键是 Include 方法-这使您可以指示哪些相关对象应该被水合.

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

修改

尝试解决基于字符串的包含问题(包含使用LINQ的嵌套实体的启发):

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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