Gernerate List using Entity Framework and lambda expressions in C#

Question

For my own practice I'm building a small ASP.NET website that shows data content of an existing database.

To work with the database I'm using Entity Framework and I want to use lambda expressions in connection.

Actual I got 6 tables in my database:

1. Projects (ID, ProjectName)
2. Categories (ID, CategoryName)
3. Users (ID, UserName)
4. Parts (ID, PartName)
5. ProjectCategoryPart (ProjectID, CategoryID, PartID, PartExists)

6. ProjectCategoryUser (ProjectID, CategoryID, UserID)

   • Each Project has n Categories
   • Each Category has 1 User
   • For each Project and Category there are n Parts with an PartExists -Flag

Now I want to create a list that contains the following information for one of the projects inside of table one

Category       User                Parts Left       Total Parts
Category_1     RelatedUserName     PartCountLeft    PartCountTotal
Category_2     RelatedUserName     PartCountLeft    PartCountTotal
Category_n     RelatedUserName     PartCountLeft    PartCountTotal

Here for example one code Line I'm actually using to get the data of a project out of the table Projects:

myList = DatabaseEntities.Projects.Single(project => project.Number == sendNumber);

Can someone help me with the code I need to create the List?

Up to now I'm only able to create simple database requests because it was hard for me to find examples that are showing more than this.

Answer 1

As explained in the comments, your design may need some work, but if you are trying to focus in on the aggregation portion you can work around it. If your classes have navigation properties similar to this:

public class Project
{
    public int Id { get; set; }  
    public string ProjectName { get; set; }

    // if you want multiple users you will need to change this
    public int UserId{ get; set; }
    public User User { get; set; }  // nav to user

    public ICollection<ProjectPart> ProjectParts { get; set; }
}

public class ProjectPart
{
    public int PartId { get; set; } // Be consistent and call this ID as below
    public string PartName { get; set; }
    public bool? PartExists { get; set; }
    public string CategoryName { get; set; }

    public int ProjectId { get; set; }
    public Project Project { get; set; }  // nav to project
}

public class User
{
    public int Id { get; set; }
    public string UserName{ get; set; }

    public ICollection<Project> Projects { get; set; }
}

Next, I would build a viewmodel for the results:

public class ProjectPartViewModel
{
    public string Category { get; set; }
    public string Name { get; set; }
    public int PartsCount { get; set; }
    public int PartsExistCount { get; set; }
}

Then the query:

var projectPartCounts = context.ProjectParts.AsNoTracking()
    .GroupBy(pp => new { pp.CategoryName, pp.Project.User.UserName })
    .Select(g => new PropjectPartsViewModel {
        Category = g.Key.CategoryName,
        Name = g.Key.UserName,
        PartsCount = g.Count(),
        PartsExistCount = g.Count(pp => pp.PartsExist == true)
    })
    .ToList();