System.InvalidOperationException: A specified Include path is not valid

Question

I'm trying to get a list of projects on the index page - but I keep on getting errors. I have tried different codes, and below is the latest one I've tried - but it's still not working. It gave me this error:

System.InvalidOperationException: A specified Include path is not valid. The EntityType 'StoreWeb.Models.Project' does not declare a navigation property with the name 'Collections'

I think it's because I don't know how to get collectionID from the Project table. For the Project table, it has collectionID is as a foreign key. (A project must have 1 collection. A collection may have projects.)

Can someone please help me? Here's what I have:

MODELS

---

Collection.cs [Modified]

---

[Table("Collection")]
public class Collection
{
    [Key]
    public string collectionID { get; set; }
    public string collectionName { get; set; }

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

---

Project.cs [Modified]

---

[Table("Project")]
public class Project
{
    [Key]
    public string projectID { get; set; }
    public string projectName { get; set; }
    public string projectCity { get; set; }
    public string collectionID { get; set; } // This is what was needed!

    public virtual Collection Collection { get; set; }
}

For the class Project, it has collectionID is as a foreign key. (A project must have 1 collection. A collection may have projects.)

---

ProductEntities.cs

---

public class ProductEntities : DbContext
{
    public DbSet<Collection> Collections { get; set; }
    public DbSet<Project>    Projects  { get; set; }
}

CONTROLLER

---

ProjectController [Modified]

---

using System.Data.Entity;

public class ProjectController : Controller
{
    ProductEntities productDB = new ProductEntities();

    //
    // GET: /Project/

    public ActionResult Index()
    {
        var projectModel = productDB.Projects.Include(m => m.Collection);
        return View(projectModel);
    }

VIEWS

---

Views/Project/Index.chtml

---

@model IEnumerable<StoreWeb.Models.Project>

@{
     ViewBag.Title = "Index";
}
<h1>PROJECTS</h1>

     @foreach (var project in Model)
     {
         <br /><a href="@Url.Action("Details", new { id = project.projectID })">@project.projectName</a> 
     }

Answer 1

Just a typo

public ActionResult Index(string project)
    {
        var projectModel = productDB.Projects.Include("Collection");
        return View(projectModel);
    }

and not "Collections"

TIP (of the day)

in your usings, add

using System.Data.Entity;

and then you can make

var projectModel = productDB.Projects.Include(m => m.Collection);

you'll avoid "string" typos.

EDIT

for your classes, if you're using code First (which you are)

remove the "ForeignKeys" (collection_id in Project, for example), and just do

//remove the "Bind Exclude"
public class Collection
{
    public int Id { get; set; }//make it int, it will be taken as the primary key
    public string collectionName { get; set; }

    public virtual IList<Project> Projects { get; set; }//make it virtual, lazy loading inside
}

in your project class

//remove any "collection_Id" property
public class Project
{
    public int Id { get; set; }//make it it, rename it, it will be taken as PK
    public string projectName { get; set; }
    public string projectCity { get; set; }

    public virtual Collection Collection { get; set; }
}

Answer 2

NOTE: FOR EF CORE 3+ or 5+:

I know this has been answered but I faced similar issue using EF Core when reverse engineering or scaffolding a database:

This issue came up with include property on the indexes in my DbContext, when I have multiple properties involved in the Indexes.

After reverse engineering or Scaffolding from DB inside my OnModelCreating method I had this:

entity.HasIndex(e => e.BusinessName, "NonClusteredIndex-20190824-150740")
                 .IncludeProperties(new[] { "Contentid", "Stateid", "Cityid", "businessurl", "UserID" });

Then I changed it to this

entity.HasIndex(e => e.BusinessName, "NonClusteredIndex-20190824-150740")
                 .IncludeProperties(bmaster => new { bmaster.Contentid, bmaster.Stateid, bmaster.Cityid, bmaster.Businessurl, bmaster.UserId });

This resolved for me. In this case, EF Core couldn't use the string parameters, I hope this will be fixed in the new release of EF Core.