Ado. Net (c)--Database Operation class

Manipulating Data classes

Avoid code reuse, too many objects, no division of labor Development

Use the object-oriented approach to optimize the way data is accessed, using the encapsulation class

Generally packaged into three classes:

1. Data connection classes provide data connection objects

A reference namespace is required: using System.Data.SqlClient;

Cases:

 Public classDbconnect {Private Static stringConnString ="server=.; Database=mydb;user=sa;pwd=123";  Public StaticSqlConnection Conn//use a static method to obtain a connection object through an object or method        {            Get{//read-only properties                return NewSqlConnection (connstring); }        }    }

2. Entity classes are based on tables in the database

For example, the Nation table builds a nation class.

Table name = class name ; encapsulated field = property inside the table

Cases:

 Public classNation {Private stringCode;  Public stringCode {Get{returnCode;} Set{Code =value;} }        Private stringname;  Public stringName {Get{returnname;} Set{name =value;} }    }

3. Data access class implementation of various operations on the table additions and deletions

A reference namespace is required: using System.Data.SqlClient;

Querying all data returns a collection that uses list< to write the type of data > Generic collection (widely used in the collection of stored objects)

Cases:

//The main implementation of the nation table of various operations (increase and deletion of check)     Public classNationda {PrivateSqlConnection _conn;//Connection Object        PrivateSqlCommand _cmd;//Command Object        PrivateSqlDataReader _dr;//Reader Object//constructs a method to initialize a Connection object command object         PublicNationda () {_conn= Dbconnect.conn;//initializing a Connection object_cmd = _conn. CreateCommand ();//initializing a Command object        }        //ways to add data         Public BOOLADD (stringCodestringname) {_cmd.commandtext="INSERT into Nation values (@code, @name)"; _cmd. Parameters.addwithvalue ("@code", code); _cmd. Parameters.addwithvalue ("@name", name); _conn.            Open (); intn =_cmd.            ExecuteNonQuery (); _conn.            Close (); if(N >0)            {                return true; }            Else            {                return false; }        }        //ways to query all data         PublicList<nation>Select () {_cmd.commandtext="SELECT * from Nation"; _conn.            Open (); _DR=_cmd.                       ExecuteReader (); //to define an empty collectionlist<nation> list =NewList<nation>(); if(_DR. HasRows) { while(_DR. Read ()) {//Create a Nation objectNation data =NewNation (); Data. Code= _dr[0].                    ToString (); Data. Name= _dr[1].                    ToString (); //throw it in the collection .list.                ADD (data); }} _conn.            Close (); returnlist; }        //method of query based on condition         PublicList<nation> Select (stringcode) {_cmd.commandtext="SELECT * from Nation where [email protected]"; _cmd.            Parameters.clear (); _cmd. Parameters.addwithvalue ("@code", code); _conn.            Open (); _DR=_cmd.            ExecuteReader (); //to define an empty collectionlist<nation> list =NewList<nation>(); if(_DR. HasRows) { while(_DR. Read ()) {//Create a Nation objectNation data =NewNation (); Data. Code= _dr[0].                    ToString (); Data. Name= _dr[1].                    ToString (); //throw it in the collection .list.                ADD (data); }} _conn.            Close (); returnlist; }        //Delete Method         Public BOOLDelete (stringcode) {_cmd.commandtext="Delete from Nation where [email protected]"; _cmd.            Parameters.clear (); _cmd. Parameters.addwithvalue ("@code", code); _conn.            Open (); intn =_cmd.            ExecuteNonQuery (); _conn.            Close (); if(N >0)            {                return true; }            Else            {                return false; }        }        //Modify Method         Public BOOLUpdate (stringCodestringname) {_cmd.commandtext="update Nation Set [email protected] where [email protected]"; _cmd.            Parameters.clear (); _cmd. Parameters.addwithvalue ("@code", code); _cmd. Parameters.addwithvalue ("@name", name); _conn.            Open (); intn =_cmd.            ExecuteNonQuery (); _conn.            Close (); if(N >0)            {                return true; }            Else            {                return false; }        }                 Public stringNationname (stringcode) {_cmd.commandtext="Select Name from Nation where [email protected]"; _cmd. Parameters.addwithvalue ("@code", code); _conn.            Open (); _DR=_cmd.            ExecuteReader (); if(_DR. HasRows) {_dr.                Read (); return_dr[0].            ToString (); }            Else            {                return "Han"; } _conn.        Close (); }    }

View Code

Viewing elements using the Foreach Traversal collection

※foreach cannot add or subtract any element, but can modify the data

Cases:

Console.WriteLine (" Please enter code:");             string code = console.readline ();            List<Nation> list = da. Select (code);             foreach inch list)            {                "--" + data. Name);            }

Ado. Net (c)--Database Operation class