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?
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?
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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