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POHow to implement Generics in business object class definition with DAL to create a proper user control dropdown
 

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  1. POHow to implement Generics in business object class definition with DAL to create a proper user control dropdown
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    <p>I am woefully new to generics, being tied to the support of a corporate intranet web application whose upgrade process is bound to red tape and slowwwly-changing standards. Consequently, today (thankfully!) I finally find myself scrambling during our upgrade to .Net 3.5 and transitioning all the code I can to a properly tiered model.</p> <p>I have been reading all morning about generics trying to digest how to transition dropdown user controls into a proper business object that gets its data from a class in the data access layer.</p> <p>There is a perfectly succinct question here that details exactly what I am interested in exploring: <a href="https://stackoverflow.com/questions/4156037/set-selected-index-in-a-dropdownlist-in-usercontrol">Set selected index in a Dropdownlist in usercontrol</a>.</p> <p>What I would love to see, however, is what <code>Travel_CarSizes.GetCarSizes()</code> actually looks like inside and how the class <code>Travel_CarSizes</code> is defined. (I am having a hard time with <code>&lt;T&gt;</code> and knowing where it should occur.)</p> <p>For my own specific circumstance at the moment I need a dropdown user control to contain location directionals (N, S, W, C/O, NW, SE, etc) that are stored in a SQL table in the DB and whose selected index needs to be able to be set by whichever page it happens to be in, when form data exists.</p> <p>I have begun to implement the model in the example from the link above but right now <strong>without using Generics</strong> because I can't figure it out:</p> <p>The dropdown user control:</p> <pre><code>public partial class DropDownStreetPrefix : System.Web.UI.UserControl { public string StreetPrefixValue { get { return ddlStreetPrefix.SelectedValue.ToString(); } set { Bind(); ddlStreetPrefix.SelectedIndex = ddlStreetPrefix.Items.IndexOf(ddlStreetPrefix.Items.FindByValue(value)); } } protected void Page_Load(object sender, EventArgs e) { if (!Page.IsPostBack) { Bind(); } } private void Bind() { if (ddlStreetPrefix.Items.Count == 0) { SqlDataReader rdr = StreetDirectionals.GetDirectionals(); ddlStreetPrefix.DataSource = rdr; ddlStreetPrefix.DataBind(); ddlStreetPrefix.DataValueField = "StreetSuffixPrefixAbbr"; ddlStreetPrefix.DataTextField = "StreetSuffixPrefixAbbr"; ListItem li = new ListItem("", ""); ddlStreetPrefix.Items.Insert(0, li); ddlStreetPrefix.SelectedIndex = 0; } } } </code></pre> <p>The <code>StreetDirectionals</code> class:</p> <pre><code>public class StreetDirectionals { private StreetDirectionals () { } public static SqlDataReader GetDirectionals () { string sqlText = "SELECT StreetSuffixPrefixAbbr FROM common..tblStreetSuffixPrefix " + "ORDER BY StreetSuffixPrefixAbbr"; SqlDataReader rdr = SqlClient.ExecuteFetchReturnDataReader( theConnectionString, CommandType.Text, sqlText); return rdr; } } </code></pre> <p>I will separate out the database interaction inside the <code>StreetDirectionals</code> class as soon as I can figure out how to change its code if I were to transform the Bind() method from my dropdown user control into this:</p> <pre><code>private void Bind() { if (!IsPostBack) { **List&lt;StreetDirectionals&gt; sd = StreetDirectionals.GetDirectionals();** ddlStreetPrefix.DataSource = sd; ddlStreetPrefix.DataTextField = "StreetSuffixPrefixAbbr"; ddlStreetPrefix.DataValueField = "StreetSuffixPrefixAbbr"; ddlStreetPrefix.DataBind(); } } </code></pre> <p>Any assistance would be sooo much appreciated!</p>
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    1. COI'm not really clear in what way you want assistance - what part of the issue do you expect Generics to help you with? Is it that you want StreetDirectionals.GetDirectionals to return a StreetDirectional class rather than a SqlDataReader?
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    2. COI believe what I want, which is what the example I cited seemed to portray, is the return of a generic list by `StreetDirectionals.GetDirectionals()` rather than a `SqlDataReader.` I would like to keep database-specific functionality restricted to the data layer. I thought (but perhaps I'm wrong?) that the example was allowing the other developer to do just that. It's quite possible I'm not asking the question correctly though, given how new I am to generics.
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