.net,asp.net-mvc-5 , Only parameterless constructors and initializers are supported in LINQ to Entitier in dropdown


Only parameterless constructors and initializers are supported in LINQ to Entitier in dropdown

Question:

Tag: .net,asp.net-mvc-5

I have this controller

public ActionResult Create()
{
    var db = new MyDbContext();
    IEnumerable<SelectListItem> items = db.FileUploadCategories

        .Select(c => new SelectListItem {
            Value = c.ParentCategoryID.ToString(),
            Text = "--" + c.CategoryName
        });

    ViewBag.Categories = items;
    return View();
}

And a view like this

 @Html.DropDownList("ParentCategoryID", (IEnumerable<SelectListItem>)ViewBag.Categories, "-- Select --", new { @class = "form-control" })

This gives me the this result on the website

<select>
<option value="0">Test</option>
<option value="1">Test</option>
<option value="1">Test</option>
<option value="2">Test</option>
<option value="2">Test</option>
</select>

As you can see, some value are the same, which is because some ParentCategoryID from the controller is the same which is correct. What I would like to do is add a "-" in the text for each text in the options which will be determined by how large the value is. I want to add 3 ' - ' in text if the value is 3 and if the value is five, I want add five '-----' before the test in text. I want a result similar to this.

<select>
<option value="0">Test</option>
<option value="1">-Test</option>
<option value="1">-Test</option>
<option value="2">--Test</option>
<option value="2">--Test</option>
</select>

Notice the lines before the test.

I have tried to update my controller to

Text = new String('-',c.ParentCategoryID) + c.CategoryName

Which gives me the error message

An exception of type 'System.NotSupportedException' occurred in EntityFramework.SqlServer.dll but was not handled in user code

Additional information: Only parameterless constructors and initializers are supported in LINQ to Entities.


Answer:

You query needs to be able to be represented as a SQL statement, but new String('-',c.ParentCategoryID) can't be. Materialize your query as a List<T> first

var items = db.FileUploadCategories.ToList().Select(c => new SelectListItem()
{
    Value = c.ParentCategoryID.ToString(),
    Text= string.Format("{0}{1}", new String('-',c.ParentCategoryID), c.CategoryName)
}).ToList();

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