从二级表（实体框架）获取数据

Question

Working on MVC 5 application, with EF.

I have 3 tables in my database. For a simple example let me use this....

• Cars
  • Id
  • CarName
• Colors
  • Id
  • ColorName
• CarsColors
  • CarId
  • ColorId

Cars and Colors are "master" tables. CarsColors, is a cross-reference table that holds various combinations.

Objective: Create a view that shows a table. For each row it will display car details. There will be a column for "Colors". In the "Colors" column there will be a comma-delineated list of colors used by that car. (This is the core of my problem.) So, for example....

 <table> <th>Cars</th> <th>Colors</th> <tr> <td>Kia Sportage</td> <td>Red, Blue, Green</td> </tr> <tr> <td>Toyota Camery</td> <td>Green, Black</td> </tr> <tr> <td>Honda Odyssey</td> <td>(nothing)</td> </tr> </table> 

I'm not sure exactly how to do this. I know with my Cars select that I can use an .Include() to include CarsColors. But, how would I go "UP" one level to get the Cars.ColorName? I need to cycle thru CarsColors in order to populate the last column of each row, but use the Colors table for the actual color name.

Thanks

Answer 1

You could use a navigation property to get the color name:

public partial class CarsColors
{
    public int CarId { get; set; }
    public int ColorId { get; set; }

    public virtual Car Car { get; set; }
    public virtual Color Color { get; set; }
}

So having an object of type CarsColors you could read the Color name as below:

obj.Color.ColorName

Something like the folowing does what you are looking for:

var cars = dbContext.Cars
                    .Include(car=>car.CarsColors)
                    .GroupBy(car=>car.CarName)
                    .Select(gr=> new 
                    {
                        CarName = gr.Key,
                        Colors = string.Join(",", gr.Select(car=>car.CarsColors.Color.ColorName))
                    });