将LINQ查询另存为变量以调用另一个LINQ查询 [英] Save LINQ Query As Variable To Call Another LINQ Query

问题描述

我有一个var类型，用于存储我想用作另一个LINQ查询的参数的LINQ查询的结果.

I have a var type storing the result of a LINQ query that I would like to use as a parameter for another LINQ query.

我正在使用控制器:

  public async Task<ActionResult> Index(String aContainer)
    {
        var partsLocations = db.PartsLocations.Include(p => p.LocationType).Include(p => p.ManufacturingPlant);
        var empty = from y in db.PartsLocations select y;

                    if (!String.IsNullOrEmpty(aContainer))
                    {              
                      var parentLoc = from a in db.PartsLocations
                                    where a.LocationName.Contains(aContainer)
                                    select a.ParentLocation;
                      var location = (from b in db.PartsLocations.Where(b => parentLoc.Equals(b.LocationID))
                                    select b).ToList();                             

                        return View( location.ToList());
                     }
        empty = empty.Where(r => r.LocationName.Contains(null));
        return View(await empty.ToListAsync());
    }

我的看法是:

@model IEnumerable<Parts.PartsLocation>

@{
    ViewBag.Title = "Index";
 }

型号:

 public int LocationID { get; set; }
    public int TypeID { get; set; }
    public string LocationName { get; set; }
    public string Description { get; set; }
    public int PlantID { get; set; }
    public Nullable<int> BayID { get; set; }
    public Nullable<int> SecurityGroupID { get; set; }
    public Nullable<int> ParentLocation { get; set; }
    public Nullable<System.DateTime> LastMoved { get; set; }
    public string Notes { get; set; }

但是我收到错误消息:无法将类型'System.Int32'强制转换为'System.Object'.LINQto Entities仅支持强制转换EDM基本类型或枚举类型."

But I am getting error: "Unable to cast the type 'System.Int32' to type 'System.Object'. LINQ to Entities only supports casting EDM primitive or enumeration types."

在SQL中，我做类似的事情:

In SQL I do something like:

从PartsLocations中的LocationName ='aContainer';

SELECT ParentLocation FROM PartsLocations where LocationName = 'aContainer';

选择* FROM PartsLocations，其中LocationID = ParentLocation;

SELECT * FROM PartsLocations where LocationID = ParentLocation;

如何将LINQ查询的结果用作单独查询的参数? 预先感谢！

How can I use the result of a LINQ query as a parameter for a separate query? Thanks in advance!

推荐答案

此

              var parentLoc = from a in db.PartsLocations
                            where a.LocationName.Contains(aContainer)
                            select a.ParentLocation;

不是结果.这是一个查询.

is not a result. It is a query.

如果需要结果，请运行查询:

If you want a result, run the query:

var location = parentLoc.Single();

尝试，类似:

              var parentLoc = (from a in db.PartsLocations
                               where a.LocationName == aContainer
                               select a.ParentLocation).Single();

              var locations = (from b in db.PartsLocations
                               where b.LocationID == parentLoc
                               select b).ToList(); 

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