I tested the three-tier structure system in Asp.net.

Display Layer/logic layer/data layer
The display layer is usually composed of. aspx/. aspx. CS files. It is used to display data pages. If the data pages are divided by three layers, the page layer should directly call the methods in the logic layer.
The logic layer is an intermediate layer used to connect the page layer and data layer. It provides interfaces to the page layer and also calls methods from the data layer for the page layer to use.
The data layer is the bottom layer, which is generally used for data operations.
Oh, now let's explain this three-tier system. Let's take a test.

Page Layer[Default. aspx]: Only one DataGrid Control and one label control.
Final execution result of the page

Default. aspx. CS File

Using system; using system. collections; using system. componentmodel; using system. data; using system. drawing; using system. web; using system. web. sessionstate; using system. web. ui; using system. web. UI. webcontrols; using system. web. UI. htmlcontrols; using lemongtree. BL; Summary of namespace services {// <summary> // _ default. /// </Summary> public class _ default: system. web. UI. page {protected system. web. UI. webcontrols. label label1; protected system. web. UI. webcontrols. dataGrid datagrid1; private void page_load (Object sender, system. eventargs e) {// place the user here Code To initialize the page if (! Page. ispostback) {setup ("select * from favor", datagrid1) ;}} private void setup (string SQL, DataGrid DG) {Blyer BL = new Blyer ("Server = lemongtree; uid = sa; Pwd = sa; database = BBS "); BL. showdatagrid (SQL, DG); label1.text = bl. error;} # region web form designer generated code override protected void oninit (eventargs e) {// codegen: The call is ASP.. NET web form designer. // Initializecomponent (); base. oninit (e) ;}/// <summary> /// the designer supports the required methods-do not use the code editor to modify the content of this method. /// </Summary> private void initializecomponent () {This. datagrid1.pageindexchanged + = new system. web. UI. webcontrols. datagridpagechangedeventhandler (this. datagrid1_pageindexchanged); this. load + = new system. eventhandler (this. page_load) ;}# endregionprivate void datagrid#pageindexchanged (Object source, system. web. UI. webcontrols. datagridpagechangedeventargs e ){}}}

Logic layer[BL. CS]

Using system; using system. text; using system. data; using system. data. sqlclient; using lemongtree. DB; using system. web. UI. webcontrols; namespace lemongtree. BL {/// <summary> /// Summary of BL. /// </Summary> public class Blyer {private string strconn; private sqlconnection objconn; private dbmaster dBm; private string errmsg; Public Blyer (string strconn) {// todo: add the constructor logic here // This. strconn = strconn; this. objconn = new sqlconnection (strconn); dBm = new dbmaster (strconn);} public string error {get {return errmsg;} public void showdatagrid (string strsql, DataGrid dgrd) {dgrd. datasource = dBm. dataset (strsql); errmsg = dBm. error; dgrd. databind ();}}}
 

Data Layer[DB. CS]

 using system; using system. text; using system. data; using system. data. sqlclient; using Microsoft. applicationblocks. data; namespace lemongtree. DB {///  /// Summary of the DB. ///  public class dbmaster {private string strconn; private string MSG; private sqlconnection objconn; Public dbmaster (string strconn) {// todo: add the constructor logic here // This. strconn = strconn; this. objconn = new sqlconnection (strconn);} public string error {get {return MSG;} public dataset (string strsql) {dataset DST = new dataset (); try {DST = sqlhelper. executedataset (strconn, commandtype. text, strsql); MSG = "Total number of records: " + DST. tables [0]. rows. count. tostring () + ""; return DST;} catch (sqlexception e) {MSG = E. message;} finally {DST. dispose () ;}return null ;}}