涉及对未直接连接的两个表进行分组的 Linq 查询

Question

在具有这些类的 EF 模型中：

 class BoxOutput
 {
     public long BoxId { get; set; }
     public virtual Box Box { get; set; }
     public long BoxId { get; set; }
     public long CategoryId { get; set; }
     public virtual Category Category { get; set; }
     public long? ColorId { get; set; }
     public virtual Category Color { get; set; }
     public decimal Weight { get; set; }

     // ...and other irrelevant properties
 }

 class BoxInput
 {
     public long BoxId { get; set; }
     public virtual Box Box { get; set; }
     public long BoxId { get; set; }
     public long CategoryId { get; set; }
     public virtual Category Category { get; set; }
     public long? ColorId { get; set; }
     public virtual Category Color { get; set; }
     public decimal Weight { get; set; }

     // ...and other irrelevant properties
 }

...我怎样才能对特定的框（例如boxId = 12）进行 LINQ 查询，返回这个？：

  category.name    color.name      inputWeightsSum      outputWeightsSum
 ---------------------------------------------------------------------------
     c             null               0                    0
     c             red                0                    0
     c             blue               0                    0
     m             null               0                    0
     m             red                0                    0
     m             blue               0                    0
                           ....

我目前几乎实现了这一点，但是在做“笛卡尔积”时，“可选颜色”给我带来了麻烦：我没有显示空值......

这就是我所拥有的。

var boxesInputs = dbContext.BoxesInputs
.Where(c => c.BoxId == 12)
.GroupBy(c => new { c.CategoryId, c.ColorId })
.Select(g => new
{
    categoryId = g.Key.CategoryId,
    colorId = g.Key.ColorId,
    sumOfWeights = g.Sum(r => (decimal?)r.Weight) ?? 0,
}).ToList();

var boxesOutputs = dbContext.BoxesOutputs
.Where(c => c.BoxId == 12)
.GroupBy(c => new { c.CategoryId, c.ColorId })
.Select(g => new
{
    categoryId = g.Key.CategoryId,
    colorId = g.Key.ColorId,
    sumOfWeights = g.Sum(r => (decimal?)r.Weight) ?? 0,
}).ToList();

var categoriesAndColors = dbContext.Categories.AsEnumerable()
.SelectMany(category => dbContext.Colors.AsEnumerable()
.Select(color => new
{
    category = new
    {
        categoryId = category.CategoryId,
        name = category.Name,
    },
    color = new
    {
        colorId = color.ColorId,
        name = color.Name,
    },
    inputWeightsSum = boxesInputs.Where(r => r.categoryId == category.CategoryId && r.colorId == color.ColorId).Sum(r => (decimal?) r.sumOfWeights) ?? 0,
    outputWeightsSum = boxesOutputs.Where(r => r.categoryId == category.CategoryId && r.colorId == color.ColorId).Sum(r => (decimal?)r.sumOfWeights) ?? 0,
})).ToList();

在前面的代码中，前两个查询返回：

  category.name    color.name      inputWeightsSum
 -------------------------------------------------------
     c             null               0
     c             red                0
     c             blue               0
     m             null               0
     m             red                0
     m             blue               0 
                           ....

  category.name    color.name      outputWeightsSum
 -------------------------------------------------------
     c             null               0
     c             red                0
     c             blue               0
     m             null               0
     m             red                0
     m             blue               0 
                           ....

第三个加入这两个。我想我需要改进那个连接，因为我正在丢失空值。

此外，此代码使用内存中的代码，我希望它是一个单 sql 查询（linq-to-entities 而不是 linq-to-objects 与 linq-to-entities 混合）。是否可以？假设 BoxOutput 和 BoxInput 是两个不同的表，并且它们没有直接连接。或者无论如何我最终都会得到 3 个查询？

Answer 1

您从两个表中选择相同的匿名类型，将它们合并在一起，然后进行分组并选择。像这样的：

dbContext.BoxesInputs
.Select(g => new TempClass
{
    CategoryId = g.CategoryId,
    ColorId = g.ColorId,
    InputWeight = r.Weight,
    OutputWeight = 0,
})
.Union(dbContext.BoxesOutputs
    .Select(g => new TempClass
    {
        CategoryId = g.CategoryId,
        ColorId = g.ColorId,
        InputWeight = 0,
        OutputWeight = r.Weight
    })
)
.GroupBy(c => new { c.CategoryId, c.ColorId })
.Select(g => new
{
    categoryId = g.Key.CategoryId,
    colorId = g.Key.ColorId,
    sumOfInputWeights = g.Sum(r => r.InputWeight),
    sumOfOutputWeights = g.Sum(r => r.OutputWeight),
}).ToList();

public class TempClass
{
    public int CategoryID { get; set; }
    public int ColorID { get; set; }
    public decimal InnerWeight { get; set; }
    public decimal OuterWeight { get; set; }
}