微软官方SqlHelper类 数据库辅助操作类 原创

数据库操作类真的没有必要自己去写，因为成熟的类库真的非常完善了，拿来直接用就好，省时省力。

本文就为大家介绍微软官方的程序PetShop4.0中的SqlHelper类，先来做一下简单的介绍，PetShop是一个范例，微软用它来展示.Net企业系统开发的能力。

那SqlHelper中封装了哪些方法呢？

里面的函数一堆，常用的就那几个，无非就是增删改查嘛，来看下几种常用的函数：

1.ExecuteNonQuery 执行增删改
2.ExecuteReader 执行查询
3.ExecuteScalar 返回首行首列

使用方法介绍

Web.config配置

<connectionStrings>
	<add name="ConnectionString" connectionString="server=127.0.0.1;uid=sa;pwd=ok;database=PetShop;Max Pool Size =512; Min Pool Size=0; Connection Lifetime = 300;packet size=1000;" providerName="System.Data.SqlClient" />
</connectionStrings>

调用函数的写法

sql = "UPDATE Student set Name = @Name WHERE Id = @Id";
SqlHelper.ExecuteNonQuery(CommandType.Text, sql, new SqlParameter[]{
 new SqlParameter("@Name", name),
 new SqlParameter("@Id", id)
});

这样调用就比较简化，而且比较灵活

源码呈上

/// <summary>
  /// The SqlHelper class is intended to encapsulate high performance, 
  /// scalable best practices for common uses of SqlClient.
  /// </summary>
  public abstract class SqlHelper
  {

    //数据库连接字符串
    public static readonly string ConnectionString = ConfigurationManager.ConnectionStrings["SQLConnString"].ConnectionString;

    #region 私有函数和方法

    /// <summary>
    /// This method is used to attach array of SqlParameters to a SqlCommand.
    /// 
    /// This method will assign a value of DbNull to any parameter with a direction of
    /// InputOutput and a value of null. 
    /// 
    /// This behavior will prevent default values from being used, but
    /// this will be the less common case than an intended pure output parameter (derived as InputOutput)
    /// where the user provided no input value.
    /// </summary>
    /// <param name="command">The command to which the parameters will be added</param>
    /// <param name="commandParameters">An array of SqlParameters to be added to command</param>
    private static void AttachParameters(SqlCommand command, SqlParameter[] commandParameters)
    {
      if (command == null) throw new ArgumentNullException("command");
      if (commandParameters != null)
      {
        foreach (SqlParameter p in commandParameters)
        {
          if (p != null)
          {
            // Check for derived output value with no value assigned
            if ((p.Direction == ParameterDirection.InputOutput ||
              p.Direction == ParameterDirection.Input) &&
              (p.Value == null))
            {
              p.Value = DBNull.Value;
            }
            command.Parameters.Add(p);
          }
        }
      }
    }

    /// <summary>
    /// This method assigns dataRow column values to an array of SqlParameters
    /// </summary>
    /// <param name="commandParameters">Array of SqlParameters to be assigned values</param>
    /// <param name="dataRow">The dataRow used to hold the stored procedure's parameter values</param>
    private static void AssignParameterValues(SqlParameter[] commandParameters, DataRow dataRow)
    {
      if ((commandParameters == null) || (dataRow == null))
      {
        // Do nothing if we get no data
        return;
      }

      int i = 0;
      // Set the parameters values
      foreach (SqlParameter commandParameter in commandParameters)
      {
        // Check the parameter name
        if (commandParameter.ParameterName == null ||
          commandParameter.ParameterName.Length <= 1)
          throw new Exception(
            string.Format(
              "Please provide a valid parameter name on the parameter #{0}, the ParameterName property has the following value: '{1}'.",
              i, commandParameter.ParameterName));
        if (dataRow.Table.Columns.IndexOf(commandParameter.ParameterName.Substring(1)) != -1)
          commandParameter.Value = dataRow[commandParameter.ParameterName.Substring(1)];
        i++;
      }
    }

    /// <summary>
    /// This method assigns an array of values to an array of SqlParameters
    /// </summary>
    /// <param name="commandParameters">Array of SqlParameters to be assigned values</param>
    /// <param name="parameterValues">Array of objects holding the values to be assigned</param>
    private static void AssignParameterValues(SqlParameter[] commandParameters, object[] parameterValues)
    {
      if ((commandParameters == null) || (parameterValues == null))
      {
        // Do nothing if we get no data
        return;
      }

      // We must have the same number of values as we pave parameters to put them in
      if (commandParameters.Length != parameterValues.Length)
      {
        throw new ArgumentException("Parameter count does not match Parameter Value count.");
      }

      // Iterate through the SqlParameters, assigning the values from the corresponding position in the 
      // value array
      for (int i = 0, j = commandParameters.Length; i < j; i++)
      {
        // If the current array value derives from IDbDataParameter, then assign its Value property
        if (parameterValues[i] is IDbDataParameter)
        {
          IDbDataParameter paramInstance = (IDbDataParameter)parameterValues[i];
          if (paramInstance.Value == null)
          {
            commandParameters[i].Value = DBNull.Value;
          }
          else
          {
            commandParameters[i].Value = paramInstance.Value;
          }
        }
        else if (parameterValues[i] == null)
        {
          commandParameters[i].Value = DBNull.Value;
        }
        else
        {
          commandParameters[i].Value = parameterValues[i];
        }
      }
    }

    /// <summary>
    /// This method opens (if necessary) and assigns a connection, transaction, command type and parameters 
    /// to the provided command
    /// </summary>
    /// <param name="command">The SqlCommand to be prepared</param>
    /// <param name="connection">A valid SqlConnection, on which to execute this command</param>
    /// <param name="transaction">A valid SqlTransaction, or 'null'</param>
    /// <param name="commandType">The CommandType (stored procedure, text, etc.)</param>
    /// <param name="commandText">The stored procedure name or T-SQL command</param>
    /// <param name="commandParameters">An array of SqlParameters to be associated with the command or 'null' if no parameters are required</param>
    /// <param name="mustCloseConnection"><c>true</c> if the connection was opened by the method, otherwose is false.</param>
    private static void PrepareCommand(SqlCommand command, SqlConnection connection, SqlTransaction transaction, CommandType commandType, string commandText, SqlParameter[] commandParameters, out bool mustCloseConnection)
    {
      if (command == null) throw new ArgumentNullException("command");
      if (commandText == null || commandText.Length == 0) throw new ArgumentNullException("commandText");

      // If the provided connection is not open, we will open it
      if (connection.State != ConnectionState.Open)
      {
        mustCloseConnection = true;
        connection.Open();
      }
      else
      {
        mustCloseConnection = false;
      }

      // Associa