将此 SQL 查询转换为 LINQ 查询

Question

我需要将此 SQL 查询转换为 LINQ 查询，还需要公开 SQL Select 属性：

SELECT Problem.ProblemID, ProblemFactory.ObjectiveID, Objective.Name, ProblemFactory.Time, ProblemType.ProblemTypeName, ProblemFactory.OperationID, 
                     ProblemFactory.Range1ID, ProblemFactory.Range2ID, ProblemFactory.Range3ID, ProblemFactory.Range4ID, 
                     ProblemFactory.MissingNumber
FROM Problem INNER JOIN ProblemFactory ON Problem.ProblemFactoryID = ProblemFactory.ProblemFactoryID
             INNER JOIN ProblemType ON ProblemFactory.ProblemTypeID = ProblemType.ProblemTypeID
             INNER JOIN Objective ON Objective.ObjectiveID = ProblemFactory.ObjectiveID

更新 1：

这就是我所拥有的：

        var query = from problem in dc.Problem2s
                    from factory
                    in dc.ProblemFactories
                         .Where(v => v.ProblemFactoryID == problem.ProblemFactoryID)
                         .DefaultIfEmpty()
                    from ...

我正在使用此示例：LINQ to 中内部联接的语法是什么SQL？

Answer 1

像这样的东西吗？

var query =
    from p in ctx.Problem
    join pf in ctx.ProblemFactory on p.ProblemFactoryID equals pf.ProblemFactoryID
    join pt in ctx.ProblemType on pf.ProblemTypeID equals pt.ProblemTypeID
    join o in ctx.Objective on pf.ObjectiveID equals o.ObjectiveID
    select new
    {
        p.ProblemID,
        pf.ObjectiveID,
        o.Name,
        pf.Time,
        pt.ProblemTypeName,
        pf.OperationID, 
        pf.Range1ID,
        pf.Range2ID,
        pf.Range3ID,
        pf.Range4ID, 
        pf.MissingNumber,
    };

但是“SQL 选择属性”是什么意思？

Answer 2

像 Linq-to-SQL 这样的 ORM 的好处之一是我们不必展平数据即可从数据库中检索数据。如果您在设计器中映射对象（即，如果您映射了它们的关系），您应该能够仅检索问题，然后根据需要获取它们的关联属性...

var problems = from problem in dc.Problem2s select problem;

foreach (var problem in problems)
{
    // you can work with the problem, its objective, and its problem type.
    problem.DoThings();
    var objective = problem.Objective;
    var type = problem.ProblemType;    
}

因此，您保留了逻辑数据层中的数据结构，而不是不易传递的匿名类型。