如何将多个 linq 语句转换为 selectmany

发布于 2024-08-07 21:58:22 字数 477 浏览 2 评论 0原文

我是 LINQ 和 lambda 函数的初学者。我想知道如何使用 selectmany 函数将多个 linq 语句转换为一个语句。

string viewname = (from a in StoredProcedureParameters.Tables[0].AsEnumerable()
                 where a.Field<string>("ViewName") == displayName
                 select a.Field<string>("View")).Single();

DateTime date = (from d in StoredProcedureParameters.Tables[0].AsEnumerable()
                select d.Field<DateTime>("Date")).First();

提前感谢您的帮助。

原文

I am a beginner with LINQ and lambda function's. I was wondering how can i convert multiple linq statement to one statement using selectmany function.

string viewname = (from a in StoredProcedureParameters.Tables[0].AsEnumerable()
                 where a.Field<string>("ViewName") == displayName
                 select a.Field<string>("View")).Single();

DateTime date = (from d in StoredProcedureParameters.Tables[0].AsEnumerable()
                select d.Field<DateTime>("Date")).First();

Thanks for help in advance.

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苹果你个爱泡泡 2024-08-14 21:58:22

如果您想要单个查询，则可以将选择值设置为匿名类型。但返回值的范围是创建类型的方法。

var result = (from a in StoredProcedureParameters.Tables[0].AsEnumerable()
                 where a.Field<string>("ViewName") == displayName
                 select new { View = a.Field<string>("View"),
                              Date = d.Field<DateTime>("Date") }).Single();

那么变量 result 将是一个具有“View”和“Date”属性的对象。但您无法从方法返回该值。如果需要返回值，可以创建一个简单的类，

public class ViewDate
{
  public string View { get; set; }
  public DateTime Date { get; set; }
}

然后使用对象初始值设定项，最终将得到包含 ViewDate 对象实例的结果，您可以从方法中返回该实例。

var result = (from a in StoredProcedureParameters.Tables[0].AsEnumerable()
                 where a.Field<string>("ViewName") == displayName
                 select new ViewDate() { View = a.Field<string>("View"),
                              Date = d.Field<DateTime>("Date") }).Single();

If you want a single query, you could have the select value be an anonymous type. But the scope of the return value is the method where the type is created.

var result = (from a in StoredProcedureParameters.Tables[0].AsEnumerable()
                 where a.Field<string>("ViewName") == displayName
                 select new { View = a.Field<string>("View"),
                              Date = d.Field<DateTime>("Date") }).Single();

then the variable result will be an object with the properties 'View' and 'Date'. You can't return this value from a method though. If you need to return the value, you could create a simple class

public class ViewDate
{
  public string View { get; set; }
  public DateTime Date { get; set; }
}

Then using an object initializer, you will end up with result containing an instance of the ViewDate object, which you can return from your method.

var result = (from a in StoredProcedureParameters.Tables[0].AsEnumerable()
                 where a.Field<string>("ViewName") == displayName
                 select new ViewDate() { View = a.Field<string>("View"),
                              Date = d.Field<DateTime>("Date") }).Single();

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