linq 用法

1.在datatable中获取最大值

 var maxValue = _roleHandler.FrmUsers.DsESssUserRole.Roles.Rows.OfType().Select(row => row["RoleID"]).Max();

2.在datatable中获取指定值没有转换成Ienumable？

var name = from device in deviceDt where device.DeviceID == addDeviceId[i] select device.Name;

3.用except获取集合差集（对象的集合） 类继承IEquatable接口

 List value = rightsList.Except(currentRights).ToList(); Except方法

  public class Rights:IEquatable
    {

        private int rightCode;

        private int rightType;

        private int rightItemId;

       #region IEquatable 成员

        bool IEquatable.Equals(Rights other)
        {
           if(object.ReferenceEquals(other,null)) return false;
           if (object.ReferenceEquals(this, other)) return true;
           return rightCode.Equals(other.rightCode) && rightType.Equals(other.rightType) && rightItemId.Equals(other.rightItemId);
        }
       public override int GetHashCode()
       {
           int code = rightCode.GetHashCode();
           int type = rightType.GetHashCode();
           int item = rightItemId.GetHashCode();
           return code ^ type ^ item;
       }
        #endregion
    }

 3.linq Except（）方法取集合差集  类型转换
 List addList = listRightId.Except(query) as System.Collections.Generic.List;