MySQL通过实例化对象参数查询实例讲解

public static string QueryByEntity<T>(T t) where T : new()
{  string resultstr = string.Empty;
  MySqlDataReader reader = null;  try
  {
    Type type = typeof(T);
    PropertyInfo[] properties = type.GetProperties();    string select = string.Format("Select * from {0} {1}", type.Name, "{0}");    string where = string.Empty;    foreach (PropertyInfo property in properties)
    {      var value = t.GetPropertyValue<T>(property);      if (value != null && !value.Equals(property.GetDefaultValue()))
      {        if (string.IsNullOrEmpty(where))
        {          where = string.Format(" where {0}='{1}' ", property.Name, value);
        }        else
        {          where = string.Format(" {0} and {1} = '{2}' ", where, property.Name, value);
        }
      }
    }    select = string.Format(select, where);
 
    MySqlConnection connection = OpenConnection();    if (connection == null)      return resultstr;
    MySqlCommand _sqlCom = new MySqlCommand(select, connection);
    reader = _sqlCom.ExecuteReader();
    List<T> tList = new List<T>();    while (reader.Read())
    {
      T t1 = new T();      foreach (PropertyInfo property in properties)
      {        if (!string.IsNullOrEmpty(reader[property.Name].ToString()))
        {
          property.SetMethod.Invoke(t1, new object[] { reader[property.Name] });
        }
      }
      tList.Add(t1);
    }
    resultstr = JsonConvert.SerializeObject(tList);
  }  catch (Exception ex)
  {
    Logging.Error(string.Format("查询数据库失败，{0}", ex.Message));
  }  finally
  {    if (reader != null)
    {
      reader.Close();
      reader.Dispose();
    }
  }  return resultstr;
}internal static class ObjectExtend
{  public static object GetPropertyValue<T>(this object obj, PropertyInfo property)
  {
    Type type = typeof(T);
    PropertyInfo propertyInfo = type.GetProperty(property.Name);    if (propertyInfo != null)
    {      return propertyInfo.GetMethod.Invoke(obj, null);
    }    return null;
  }  public static object GetDefaultValue(this PropertyInfo property)
  {    return property.PropertyType.IsValueType ? Activator.CreateInstance(property.PropertyType) : null;
  }
}