ADO.NET中数据库连接方式
一.用SqlConnection连接SQL Server
1.加入命名空间
using System.Data.SqlClient;
2.连接数据库
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改进(更通用)的方法:
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二.用OleDbConnection连接
1.加入命名空间
using System.Data.OleDb;
2.连接sql server
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3.连接Access(可通过建立.udl文件获得字符串)
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4.连接Oracle(也可通过OracleConnection连接)
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三.创建Command对象
1.SqlCommand 构造函数
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2.建立SqlCommand与SqlConnection的关联。
myCommand.Connection = myConnection;
或者:SqlCommand myCommand = myConnection.CreateCommand;
3.设置SqlCommand的查询文本。
myCommand.CommandText = "Select * FROM mindata";
或者第2种构造:SqlCommand myCommand = new SqlCommand(mySelectQuery);
给SqlCommand对象提供两个查询字符串,每个查询字符串访问不同的表,返回不同的结果集。两个查询语句用分号分隔。
4. 执行命令。
ExecuteReader
返回一行或多行
ExecuteNonQuery
对 Connection 执行 Transact-SQL 语句并返回受影响的行数(int)
ExecuteScalar
返回单个值(如一个聚合值).返回结果集中第一行的第一列。忽略额外的列或行
ExecuteXmlReader
将 CommandText 发送到 Connection 并生成一个 XmlReader 对象。
SqlDataReader myReader = myCommand.ExecuteReader();
或SqlDataReader myReader = myCommand.ExecuteReader(CommandBehavior.CloseConnection);
while(myReader.Read()) //循环读取数据
{
Console.WriteLine(myReader.GetString(0));// 获取指定列的字符串形式的值
Console.WriteLine(myReader. GetValue(1));// 获取以本机格式表示的指定列的值
}
CommandText = "select count(*) as NumberOfRegions from region";
Int count = (int) myCommand.ExecuteScalar();
关于OleDbCommand对象的使用。
四.DataReader的使用
1.遍历结果集
while (myReader.Read())
Console.WriteLine("tt", myReader.GetInt32(0), myReader.GetString(1));
myReader.Close();
2.使用序数索引器。
while (myReader.Read())
Console.WriteLine("tt", myReader[0].ToString(), myReader[1].ToString());
myReader.Close();
3.使用列名索引器。
while (myReader.Read())
Console.WriteLine("tt", myReader["code"].ToString(), myReader["name"].ToString());
myReader.Close();
4.使用类型访问器。
public char GetChar(int i); 获取指定列的单个字符串形式的值
public DateTime GetDateTime(int i); 获取指定列的 DateTime 对象形式的值
public short GetInt16(int i); 获取指定列的 16 位有符号整数形式的[C#]
public string GetString(int i); 获取指定列的字符串形式的值