EntityDataSource和DropDown

Question

I have two dropdownlist in my project that bind from EntityDataSource. second Dropdownlist must bind base on first DropDownlist. How can I do this?

Answer 1

If you are using ASP.net AJAX, AJAX control toolkit has a control called "Cascading DropDown", you can use it.

MS Sample

Answer 2

You can do it like this if you need no postbacks:

<select id="s1" >
    <option>-----</option>
    <option>item 1</option>
    <option>item 2</option>
    <option>item 3</option>
</select>

<br />

<select id="s2" >
</select>​

<script type="text/javascript">
    var s1 = document.getElementById("s1");
    var s2 = document.getElementById("s2");

    s1.onchange = function () {
        s2.options.length = 0;
        var value = this.value;

        if (value != "-----") {
            var opt = document.createElement("OPTION");
            opt.text = "sub " + value;
            opt.value = "sub " + value;
            s2.options.add(opt);
        }
    }
</script>

Or you can do the same kind logic on the server side but this will bring postbacks to the scene.

Answer 3

Assume Entity1 with ID, Name as properties and Entity2 with ID,Entity1ID,OrderNumber as properties.

Bind

`Dropdownlist1.Datasource = list(of Entity1)
 Dropdownlist1.DataValueField = "ID"
 Dropdownlist1.DataTextField = "Name"
 Dropdownlist1.databind()`

On selectedvalue change event of dropdownlist1 check whether user has selected valid value and then do linq search from Entity2 datasource and bind it to Dropdownlist2.

You can also go for cascading dropdownlist as mentioned by Avani.