用C#操作数据库——数据库使用SQL Server为例,对应的namespace是System.Data.SqlClient.
- 读取数据
从数据库中读取数据是最基本的操作了。
示例代码如下:
String connString = @""; // Connection string
SqlConnection conn = new SqlConnection(connString);
try
{
String queryString = @"SELECT [ID], [NAME] FROM dbo.TABLE1;";
conn.Open();
SqlCommand cmd = new SqlCommand(queryString, conn);
SqlDataReader reader = cmd.ExecuteReader();
while(reader.Read())
{
Console.Write(reader.GetInt32(0)); // ID
Console.Write(reader.GetString(1)); // Name
}
}
catch(Exception exp)
{
System.Diagnostics.Debug.WriteLine(exp.Message);
}
finally
{
conn.Close();
conn.Dispose();
}
- 写入数据
与读取数据旗鼓相当的支柱型操作就是写入了。
一个简单的写入示例(这里使用了一个await操作以达到异步的效果):
String connString = @""; // Connection string
SqlConnection conn = new SqlConnection(connString);
try
{
String queryString = @"INSERT INTO dbo.TABLE1 ([ID], [Name]) VALUES(1, 'Test')";
conn.Open();
SqlCommand cmd = new SqlCommand(queryString, conn);
try
{
Int32 nRst = await cmd.ExecuteNonQueryAsync();
}
catch(Exception exp)
{
System.Diagnostics.Debug.WriteLine(exp.Message);
}
}
catch (Exception exp)
{
System.Diagnostics.Debug.WriteLine(exp.Message);
}
finally
{
conn.Close();
conn.Dispose();
}
- Transaction支持
同时写入多个有关联的表时,就需要transaction的支持了。
一个示例如下:
String connString = @""; // Connection string
SqlConnection conn = new SqlConnection(connString);
try
{
conn.Open();
SqlTransaction trans = conn.BeginTransaction();
try
{
String queryString = @"INSERT INTO dbo.TABLE1 ([ID], [Name]) VALUES(1, 'Test')";
SqlCommand cmd = new SqlCommand(queryString, conn);
cmd.Transaction = trans;
Int32 nRst = await cmd.ExecuteNonQueryAsync();
queryString2 = @"INSERT INTO dbo.TABLE2 ([ID], [Name]) VALUES(2, 'Test2')";
cmd = new SqlCommand(queryString2, conn);
cmd.Transaction = trans;
nRst = await cmd.ExecuteNonQueryAsync();
trans.Commit();
}
catch(Exception exp)
{
System.Diagnostics.Debug.WriteLine(exp.Message);
trans.Rollback();
}
}
catch (Exception exp)
{
System.Diagnostics.Debug.WriteLine(exp.Message);
}
finally
{
conn.Close();
conn.Dispose();
}
- 参数支持
上述的代码片中,插入数据库中的是固定文本。而现实生活中,插入数据库绝大多数是变量——比如用户输入的内容,这时就需要用到参数。
String connString = @""; // Connection string
SqlConnection conn = new SqlConnection(connString);
try
{
String queryString = @"INSERT INTO dbo.TABLE1 ([ID], [Name]) VALUES(@id, @name)";
conn.Open();
SqlCommand cmd = new SqlCommand(queryString, conn);
cmd.Parameters.AddWithValue( "@id" , 3);
cmd.Parameters.AddWithValue( "@name" , 'Test');
try
{
Int32 nRst = await cmd.ExecuteNonQueryAsync();
}
catch(Exception exp)
{
System.Diagnostics.Debug.WriteLine(exp.Message);
}
}
catch (Exception exp)
{
System.Diagnostics.Debug.WriteLine(exp.Message);
}
finally
{
conn.Close();
conn.Dispose();
}
- Identity Value的获取
另外一个经常碰到的问题是,当table中一个Column设置为identity时候,需要取出刚insert成功的数据所获得的ID。
String connString = @""; // Connection string
SqlConnection conn = new SqlConnection(connString);
try
{
// ID is set to identity
String queryString = @"INSERT INTO dbo.TABLE1 ([Name]) VALUES(@name); SELECT @Identity = SCOPE_IDENTITY();";
conn.Open();
SqlCommand cmd = new SqlCommand(queryString, conn);
cmd.Parameters.AddWithValue( "@name" , 'Test');
SqlParameter idparam = cmd.Parameters.AddWithValue("@Identity", SqlDbType.Int);
idparam.Direction = ParameterDirection.Output;
try
{
Int32 nRst = await cmd.ExecuteNonQueryAsync();
Int32 newID = (Int32)idparam.Value;
}
catch(Exception exp)
{
System.Diagnostics.Debug.WriteLine(exp.Message);
}
}
catch (Exception exp)
{
System.Diagnostics.Debug.WriteLine(exp.Message);
}
finally
{
conn.Close();
conn.Dispose();
}
是为之记。
Alva Chien
2016.6.29