使用LINQ复杂GROUP

本文关键字：GROUP 复杂 LINQ 使用 | 更新日期: 2023-09-27 18:28:16

我熟悉LINQ中的简单GROUP BY操作。但我有一个复杂的场景。我需要使用group by将CostPageRow记录转换为CostPageSelection域对象。如何从列表中获取域对象？

注：我在上面写的小组没有给出列表。我不知道该怎么写。CostPageSelection里面有一个列表。

List<CostPageRow> costPageRows = searchDAL
    .GetAllCostPages(contextObject, searchCriteria);

var orderGroups = costPageRows
     .GroupBy(x => new { 
         x.CostPage, 
         x.Description, 
         x.BillTypeDirect,
         x.BillTypeWarehouse,
         x.OrderType,
         x.Vendor,
         x.VendorID 
     })
     .Select(y => new CostPageParent { 
           CostPage = y.First().CostPage 
     })
     .ToList();

存储过程的结果

public class CostPageRow
{
    //CostPage Parent
    public string CostPage { get; set; }
    public string Description { get; set; }
    public string Vendor { get; set; }
    public string VendorID { get; set; }
    public string BillTypeDirect { get; set; }
    public string BillTypeWarehouse { get; set; }
    public string OrderType { get; set; }
    //Item Chilld
    public string ItemID { get; set; }
    public string ItemDescription { get; set; }
    public string BrandCode { get; set; }
    public string PackSize { get; set; }
}

领域模型

public class CostPageSelection
{
    public CostPageParent CostPageParent { get; set; }
    public List<ItemChild> ChildItems { get; set; }
}

//CostPageParent
public class CostPageParent
{
    public int? SelectedCostPageID { get; set; }
    public string CostPage { get; set; }
    public string Description { get; set; }
    public string Vendor { get; set; }
    public string VendorID { get; set; }
    public string BillTypeDirect { get; set; }
    public string BillTypeWarehouse { get; set; }
    public string OrderType { get; set; }
}
//ItemChild
public class ItemChild
{
    public int? SelectedItemID { get; set; }
    public string ItemID { get; set; }
    public string ItemDescription { get; set; }
    public string BrandCode { get; set; }
    public string PackSize { get; set; }
}

使用LINQ复杂GROUP

从您的问题来看，您的数据库似乎包含父子关系的扁平层次结构，如果对数据库模式进行规范化以避免数据重复会更好：换句话说，每个CostPageRow行都应该包含对包含相关CostPageParent实例的不同表的引用（但我认为您已经有一个正在运行的数据库，这不是一个选项）。

要解决当前的问题，您需要从每个CostPageRow实例中提取定义单个组的属性（这些属性将形成一个新的CostPageParent实例），然后使用这些CostPageParent实例作为唯一键创建组，最后将组投影到CostPageSelection的新实例（每个实例都有一个唯一的CostPageParent键）。

创建组密钥后，您需要修改代码以使用IGrouping<T>.Key属性来获取组密钥：

var groups = costPageRows
    .GroupBy(x => new CostPageParent()
        {
            CostPage = x.CostPage,
            Description = x.Description,
            BillTypeDirect =  x.BillTypeDirect,
            BillTypeWarehouse = x.BillTypeWarehouse,
            OrderType = x.OrderType,
            Vendor = x.Vendor
        }, 
        new CostPageParentEqualityComparer())
    .Select(y => new CostPageSelection
        {
            CostPageParent = y.Key,
            ChildItems = y.Select(i => 
                new ItemChild()
                { 
                    BrandCode = i.BrandCode,
                    ItemDescription = i.ItemDescription,
                    ItemID = i.ItemID,
                    PackSize = i.PackSize
                })
                .ToList()
        })
    .ToList();

请注意，您需要指定IEqualityComparer<CostPageParent>实现以使分组工作属性：

class CostPageParentEqualityComparer : IEqualityComparer<CostPageParent>
{
    public bool Equals(CostPageParent x, CostPageParent y)
    {
        if (x == null)
            return y == null;
        if (object.ReferenceEquals(x, y))
            return true;
        return 
            x.BillTypeDirect == y.BillTypeDirect &&
            x.BillTypeWarehouse == y.BillTypeWarehouse &&
            ...
    }
    public int GetHashCode(CostPageParent obj)
    {
        var x = 31;
        x = x * 17 + obj.BillTypeDirect.GetHashCode();
        x = x * 17 + obj.BillTypeWarehouse.GetHashCode();
        ...
        return x;
    }
}

我想你正在寻找这样的东西：

var orderGroups = costPageRows
 .GroupBy(x => new { 
     x.CostPage, 
     x.Description, 
     x.BillTypeDirect,
     x.BillTypeWarehouse,
     x.OrderType,
     x.Vendor,
     x.VendorID 
 })
 // The following statement is basically a let statement from query expression
 .Select(y => new {
      y, 
      first = y.First()
 })
 // What happens next is projection into the CostPageSelection type using z.first
 // and then all the grouped items in z are projected into the ItemChild type
 .Select(z => new CostPageSelection {
      new CostPageParent { 
          z.first.CostPage, 
          // other props 
          ChildItems = z.Select(i => new ItemChild {
              i.ItemID,
              // other props 
          }).ToList()
 })
 .ToList();
相关文章：