如何从MVC控制器中的Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable获取值 [英] How to get value from Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable in mvc controller

问题描述

我知道标题有些复杂，但是让我通过解释问题来清除标题。

I know the title is somewhat complicate but let I clear the title by explaining the problem.

根据图片我想在搜索文本框中过滤产品名称。例如：在搜索文本框中，如果我在数据表中输入的油是整个数据想要显示哪个产品名称是油。

As per image I want to filter product name in search textbox. For ex: In search textbox if I enter the oil that in datatable whole data want to show which product name is oil.

对于过滤器，我使用linq查询，这是我的代码，

For filter I used linq query, here is my code,

var dataList = (from x in query
    select new
    {
        PartName = _Db.Part.Where(z => z.Id == x.Select(p => p.PartId).FirstOrDefault()).Select(p => p.Name),
        ManufacturerName = _Db.Manufacture.Where(z => z.Id == x.Select(p => p.ManufacturerId).FirstOrDefault()).Select(p => p.name),
        CategoryName = _Db.Category.Where(z => z.Id == x.Select(p => p.CategoryId).FirstOrDefault()).Select(p => p.Name),
        Pcs = x.Sum(o =>o.Pcs) - 
        (from m in _Db.MaterialRecord
           join s in _Db.ServiceJob on m.ServiceJobId equals s.Id
           where m.pid == x.Select(p => p.PartId).FirstOrDefault()
           select m).Sum(z => z.Qty),
        Weight = _Db.Purchase.Where(p => p.Weight == x.Select(s => s.Weight).FirstOrDefault()).Select(a => a.Weight).FirstOrDefault(),      
        WeightType = x.Select(p => p.WeightTypeId).FirstOrDefault() > 0 ?((WeightType)x.Select(p => p.WeightTypeId).FirstOrDefault()).ToString() :"",
    }).ToList();

//Search    
if (!string.IsNullOrEmpty(searchValue))
    dataList = dataList.Where(m => m.CategoryName.Contains(searchValue.ToString().ToLower())).ToList();

//Returning Json Data
return Json(new { draw = draw, recordsFiltered = recordsTotal, recordsTotal = recordsTotal, data = data });

根据代码，我正在datalist变量中获取整个数据。现在，当我那时在搜索框中搜索任何产品时，搜索的条件将为true，此后数据列表值将为null（如调试代码所示）。

As per code I am getting whole data in datalist variable. Now, when I search any product in searchbox at that time the condition of search will true and after that the datalist value will be null[as shown by debug the code].

因此，因此从该数据表中显示空数据。

So, hence from that datatable shows null data.

为了理解为什么会发生这种情况，我在类别的数据列表查询中添加了 tostring（）行，即

For understanding that why this happening I add the tostring() in datalist query of category line i.e.

CategoryName = _Db.Category.Where(z => z.Id == x.Select(p => p.CategoryId).FirstOrDefault()).Select(p => p.Name).toString(),

在此行中添加 toString（）后，它将显示此行 Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable 。但是我想要这条线的结果值。为了更清晰，让我们看一下另一张图片

After adding toString() in this line it shows this line Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable. But I want the result value of this line. For more clear lets see the another image

我要在搜索条件行中找到的 oil 结果值，即

That oil result value I want in search condition line i.e.

dataList = dataList.Where(m => m.CategoryName.Contains(searchValue.ToString().ToLower())).ToList();

但现在其中显示此行 Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable 代替结果值。

but right now in it is showing this line Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable in the place of result value.

推荐答案

您应该知道的第一件事是 ToString（） 的默认实现是在应用于集合对象时返回对象的标准名称，在这种情况下，返回 Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable< string> 是不覆盖该方法的引用类型。

First thing you should know is ToString() by its default implementation returns fully-qualified name of the object when applied to collection objects, in this case returns Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable<string> which is a reference type that doesn't override that method.

让我们首先评估该表达式：

Let's evaluate this expression first:

CategoryName = _Db.Category.Where(z => z.Id == x.Select(p => p.CategoryId).FirstOrDefault())
                           .Select(p => p.Name),

假定类别具有 DbSet< Category> ; 类型，上面代码中使用的 Select（）扩展方法返回 EntityQueryable< string> ，其中包含LINQ-to-Entities查询提供的已执行SQL语句的结果集集合。如果要从该集合中提取单个字符串值，则必须使用 First（）， Single（）， FirstOrDefault（）或 SingleOrDefault（）扩展方法。

Assumed that Category has DbSet<Category> type, the Select() extension method used in code above returns EntityQueryable<string> which contains result set collection from executed SQL statement provided by LINQ-to-Entities query. If you want to pull single string value from that collection, you must use one of the First(), Single(), FirstOrDefault() or SingleOrDefault() extension methods.

因此，您应该如上所述添加扩展方法以返回字符串值而不是集合：

Hence, you should add extension method as mentioned above to return a string value instead of a collection:

var dataList = (from x in query
    select new {
        // other properties

        CategoryName = _Db.Category.Where(z => z.Id == x.Select(p => p.CategoryId).FirstOrDefault())
                               .Select(p => p.Name).SingleOrDefault(),

        // other properties
    }).ToList();

然后您可以对子字符串使用 Contains （ searchValue ），因为 CategoryName 具有字符串类型：

Then you can use Contains against a substring (searchValue) because CategoryName has string type:

dataList = dataList.Where(m => m.CategoryName.Contains(searchValue.ToString().ToLower())).ToList();

参考：

实体框架/核心和LINQ到实体的查询方法（操作员）

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