C#中DataTable 转实体实例详解

速度确实快了很多，我电脑测试了一下，需要 0.4秒。但问题又来了，这个只能用于Usr这个类，得想办法把这个类抽象成泛型T，既有委托的高效，又有泛型的通用。

问题就在动态地产生上面的委托了，经过一下午的折腾终于折腾出来了动态产生委托的方法。主要用到了动态Lambda表达式

public static class EntityConverter
  {
    /// <summary>
    /// DataTable生成实体
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="dataTable"></param>
    /// <returns></returns>
    public static List<T> ToList<T>(this DataTable dataTable) where T : class, new()
    {
      if (dataTable == null || dataTable.Rows.Count <= 0) throw new ArgumentNullException("dataTable", "当前对象为null无法生成表达式树");
      Func<DataRow, T> func = dataTable.Rows[0].ToExpression<T>();
      List<T> collection = new List<T>(dataTable.Rows.Count);
      foreach (DataRow dr in dataTable.Rows)
      {
        collection.Add(func(dr));
      }
      return collection;
    }
    /// <summary>
    /// 生成表达式
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="dataRow"></param>
    /// <returns></returns>
    public static Func<DataRow, T> ToExpression<T>(this DataRow dataRow) where T : class, new()
    {
      if (dataRow == null) throw new ArgumentNullException("dataRow", "当前对象为null 无法转换成实体");
      ParameterExpression paramter = Expression.Parameter(typeof(DataRow), "dr");
      List<MemberBinding> binds = new List<MemberBinding>();
      for (int i = 0; i < dataRow.ItemArray.Length; i++)
      {
        String colName = dataRow.Table.Columns[i].ColumnName;
        PropertyInfo pInfo = typeof(T).GetProperty(colName);
        if (pInfo == null) continue;
        MethodInfo mInfo = typeof(DataRowExtensions).GetMethod("Field", new Type[] { typeof(DataRow), typeof(String) }).MakeGenericMethod(pInfo.PropertyType);
        MethodCallExpression call = Expression.Call(mInfo, paramter, Expression.Constant(colName, typeof(String)));
        MemberAssignment bind = Expression.Bind(pInfo, call);
        binds.Add(bind);
      }
      MemberInitExpression init = Expression.MemberInit(Expression.New(typeof(T)), binds.ToArray());
      return Expression.Lambda<Func<DataRow, T>>(init, paramter).Compile();
    }
  }