Linq查询表列列表

Question

Hi I am trying to output a list of items from a table over linq to a dropdown list

I am getting an error on the linq query: Cannot implicitly convert generic.list<string> to generic.List<locations>

Can someone help please? Thanks in advance.

public static void getlocation()
{

    DataClasses_AbintegroDataContext dc = new DataClasses_AbintegroDataContext();

    List<Location> locations = (
        from a 
            in dc.Locations 
        select a.Name).ToList();

    DropDownList ddLocation = new DropDownList();

    locations.ToList();

    ddLocation.DataSource = locations;
    ddLocation.DataBind();

    ddLocation.SelectedIndex = 0;

}

Answer 1

You are selecting a single column select a.Name and then you are trying to store the result of ToList to List<Locations> . Your current query would probably result in List<string> which is not assignable to List<Locations>

You can fix that by selecting select a

List<Location> locations = (
        from a in dc.Locations 
        select a).ToList();

You also don't need locations.ToList(); in your code, since locations is already a list. That is just redundant and you are not even assigning the result of ToList to any other field.

Edit: You need to set DataTextField and DataValueField property of your DropDownList as well like:

ddLocation.DataValueField = "ID"; //Whatever you need the ID to be when selected
ddlLocation.DataTextField = "Name";

If you just want to show names and your selected value would be name as well then you can do:

 DataClasses_AbintegroDataContext dc = new DataClasses_AbintegroDataContext();

    List<string> locations = (
        from a in dc.Locations 
        select a.Name).ToList();

    DropDownList ddLocation = new DropDownList();

    ddLocation.DataSource = locations;
    ddLocation.DataBind();
    ddLocation.SelectedIndex = 0;

Not really sure why you need to create ddlLocation inside your code, You can create that in ASPX code and just do the binding in code behind.