Entity Framework 6 + C# passing a combobox.SelectedValue as a parameter for context.CreateQuery something simple i am missing?

Question

ObjectContext context = ((IObjectContextAdapter)db).ObjectContext; 
string queryString = @"SELECT VALUE c FROM Product AS c WHERE c.ProductType = " + comboBox1.SelectedValue; 
ObjectQuery<Product> productQuery = context.CreateQuery<Product>( queryString, comboBox1.SelectedValue ); 

// I am having trouble passing combobox.selectedvalue as a parameter –

Answer 1

I will tell you the reason in a bit. Let's go through this code first so I can explain what the issue could be.

Here is a Person class:

public class Person 
{
   public int Age { get; set; }
   public string Name { get; set; }
}

Here is a list we will bind the combobox to:

var persons = new List<Person>() { new Person { Age = 35, Name = "George" } };

Here are different ways to set the binding:

comboBox1.DataSource = persons;

comboBox1.DisplayMember = "Name";
comboBox1.ValueMember = "Name";

combobox1.SelectedValue will return "George".

Here is another way to set the binding:

comboBox1.DataSource = persons;

comboBox1.DisplayMember = "Name";

combobox1.SelectedValue will return a Person object.

Your issue is most likely because SelectedValue is not returning what you expect it to return.

Answer 2

You have to add a parameter to your query, that is:

var context = ((IObjectContextAdapter)db).ObjectContext;

var queryString = @"SELECT VALUE c FROM Product AS c WHERE c.ProductType = @productType";

var productQuery = context.CreateQuery<Product>(queryString, new ObjectParameter("productType", comboBox1.SelectedValue);