英文:
How to get all unique records with the maximum value in column using LINQ
问题
给定这些数据，如何获取所有具有最高尝试次数的独特学生姓名？
我尝试获取以下结果：
学习者 | 评估Id | 尝试次数
------------------------------------
Parker | 1 | 3
Stark | 1 | 1
Rogers | 1 | 2
我该如何在LINQ中用单个查询来实现这个目标？
from la in _context.LearnerAssessments
where la.AssessmentId == assessmentId
&& learnerIds.Contains(la.LearnerId)
&& la.Attempt == {最高尝试次数}
英文:
Learner | AssesmentId | Attempt
------------------------------------
Parker | 1 | 1
Parker | 1 | 2
Stark | 1 | 1
Rogers | 1 | 1
Rogers | 1 | 2
Parker | 1 | 3
Given this data, how do I get all the unique Student name with the highest Attempt?
I'm attempting to get this result:
Learner | AssesmentId | Attempt
------------------------------------
Parker | 1 | 3
Stark | 1 | 1
Rogers | 1 | 2
How can I do this in a single query in LINQ?
from la in _context.LearnerAssessments
where la.AssessmentId == assessmentId
&& learnerIds.Contains(la.LearnerId)
&& la.Attempt == {highest attempt}
答案1
得分: 2
以下是您要翻译的代码部分：
var data = from list in _context.LearnerAssessments
group list by new
{
list.Learner,
list.AssesmentId
}
into g
select new
{
g.Key.Learner,
g.Key.AssesmentId,
Max= g.Max(x=>x.Attempt)
};
或者使用 Fluent API：
var data = _context.LearnerAssessments.GroupBy(l => new { l.Learner, l.AssesmentId }, (keys, item) => new
{
Key = keys,
MaxAttemp = item.Max(x => x.Attempt)
}).Select(x => new LearnerAssessment
{
Learner = x.Key.Learner,
Attempt = x.MaxAttemp,
AssesmentId = x.Key.AssesmentId
});
英文:
var data = from list in _context.LearnerAssessments
group list by new
{
list.Learner,
list.AssesmentId
}
into g
select new
{
g.Key.Learner,
g.Key.AssesmentId,
Max= g.Max(x=>x.Attempt)
};
or using fluent API :
var data = _context.LearnerAssessments.GroupBy(l => new { l.Learner, l.AssesmentId }, (keys, item) => new
{
Key = keys,
MaxAttemp = item.Max(x => x.Attempt)
}).Select(x => new LearnerAssessment
{
Learner = x.Key.Learner,
Attempt = x.MaxAttemp,
AssesmentId = x.Key.AssesmentId
});
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