Question

My app in ASP.NET C#. I use Linq to Sql, look the picuture

// 5 data talbe :

// Unit table

     id |   name    | unit_type_id          Unit_type   
       -------------------------                    
        1 | Unit 1  |     1                     id   |  name
        2 | Unit 2  |     1                     -------------   
        3 | Unit 3  |     1                     1    |  Type 1
        4 | Unit 4  |     2                     2    |  Type 2
        5 | Unit 5  |     1                     3    |  Type 3
        6 | Unit 6  |     3     




 //Tool table                                // tool_type   table

    id  |   name    | tool_type_id              id   |  name
    ----------------------------            ------------------- 
    1   |   Tool 1  |     1                     1    |  Tool_type 1
    2   |   Tool 2  |     2                     2    |  Tool_type 2
    3   |   Tool 3  |     1                     3    |  Tool_type 3
    4   |   Tool 4  |     2         
    5   |   Tool 5  |     3 

//unit_tool table

unit_id | tool_id
    ---------------
    1   |    1
    2   |    1
    1   |    2
    1   |    3
    2   |    2
    2   |    3
    3   |    3
    3   |    2

I want to use linq to sql in C# to get data like

// Table data i want to get

Unit name  |  Unit type name  | Tool name
-------------------------------------------------
Unit 1     | Type 1           | tool 1, tool 2, tool 3
Unit 2     | Type 1           | tool 1, tool 2, tool 3
Unit 3     | Type 1           | tool 2, tool 3
Unit 4     | Type 2           | 
Unit 5     | Type 1           | 
Unit 6     | Type 3           | 

My code be low

// Create new class

public class unit_list
    {
        //Unit name
        public string unit_name { get; set; }
        // Unit type name
        public string unit_type_name { get; set; }
        // Tool name
        public string tool_name { get; set; }
    }

// Function get data

protected void show_unit()
{
    // Create datacontext
    for_testDataContext db = new for_testDataContext();
    //Query data
    IQueryable<unit_list> CourseList = from cl in db.units
                                        select new unit_list()
                                        {
                                            unit_name = cl.name,
                                            unit_type_name = cl.unit_type.name,
                                            tool_name = // how to get data like "tool1, tool 2, tool 3"
                                        };

}

Answer 1

You should be able to write something like this (assuming all the relationships are set up correctly in Linq):

select new unit_list()
{
    unit_name = cl.name,
    unit_type_name = cl.unit_type.name,
    tool_name = string.Join(", ", 
        cl.unit_tools.Select(ut => ut.tool.name).ToArray()
    )
};

In other words..

1. Get the one-to-many relationship to unit_tools
2. Select the corresponding row in tool and select the name column
3. Join to get a single comma-separated string