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;
    }
}