在过滤之前将函数应用于列

Question

我在我的数据库中有一个列coordinates,现在坐标列包含有关对象在我的图形中占用的时间范围的信息.我想允许用户按日期过滤,但问题是我使用函数来正常确定日期.采取:

# query_result is the result of some filter operation
for obj in query_result:
    time_range, altitude_range = get_shape_range(obj.coordinates)
    # time range for example would be "2006-06-01 07:56:17 - ..."

现在,如果我想按日期过滤,我希望是like:

query_result = query_result.filter(
    DatabaseShape.coordinates.like('%%%s%%' % date))

但问题是,申请我首先需要get_shape_range对coordinates以接收一个字符串.有没有办法......我猜一个transform_filter操作？这样在like发生之前,我将一些函数应用于坐标？在这种情况下,我需要编写一个get_time_range只返回时间的函数,但问题仍然是一样的.

---

编辑:这是我的数据库类

class DatabasePolygon(dbBase):
    __tablename__ = 'objects'

    id = Column(Integer, primary_key=True)  # primary key
    tag = Column(String)  # shape tag
    color = Column(String)  # color of polygon
    time_ = Column(String)  # time object was exported
    hdf = Column(String)  # filename
    plot = Column(String)  # type of plot drawn on
    attributes = Column(String)  # list of object attributes
    coordinates = Column(String)  # plot coordinates for displaying to user
    notes = Column(String)  # shape notes
    lat = Column(String)

    @staticmethod
    def plot_string(i):
        return constants.PLOTS[i]

    def __repr__(self):
        """
        Represent the database class as a JSON object. Useful as our program
        already supports JSON reading, so simply parse out the database as
        separate JSON 'files'
        """
        data = {}
        for key in constants.plot_type_enum:
            data[key] = {}
        data[self.plot] = {self.tag: {
            'color': self.color,
            'attributes': self.attributes,
            'id': self.id,
            'coordinates': self.coordinates,
            'lat': self.lat,
            'notes': self.notes}}
        data['time'] = self.time_
        data['hdfFile'] = self.hdf
        logger.info('Converting unicode to ASCII')
        return byteify(json.dumps(data))

我正在使用sqlite 3.0.大多数事情背后的原因都是字符串,因为要存储在数据库中的大多数值都是作为字符串发送的,因此存储很简单.我想知道我是否应该使用之前的函数来完成所有这些解析魔法,并且只有更多的数据库条目？对于像十进制time_begin,time_end,latitude_begin这样的东西,而不是一个包含我解析时间范围的字符串,以便在我过滤时找到time_begin和time_end

Answer 1

我认为你应该在将字符串存储到数据库之前将其解析为列.让数据库完成它的设计工作!

CREATE TABLE [coordinates]
(
  id                INTEGER  NOT NULL PRIMARY KEY,
  tag               VARCHAR2(32),
  color             VARCHAR2(32)    default 'green',
  time_begin        TIMESTAMP,
  time_end          TIMESTAMP,
  latitude_begin    INT
);

create index ix_coord_tag on coordinates(tag);
create index ix_coord_tm_beg on coordinates(time_begin);

insert into coordinates(tag, time_begin, time_end, latitude_begin)
values('tag1', '2006-06-01T07:56:17', '2006-06-01T07:56:19', 123);

insert into coordinates(tag, time_begin, time_end, latitude_begin)
values('tag1', '2016-01-01T11:35:01', '2016-01-01T12:00:00', 130);

insert into coordinates(tag, color, time_begin, time_end, latitude_begin)
values('tag2', 'blue', '2014-03-03T20:11:01', '2014-03-03T20:11:20', 2500);

insert into coordinates(tag, color, time_begin, time_end, latitude_begin)
values('tag2', 'blue', '2014-03-12T23:59:59', '2014-03-13T00:00:29', 2978);

insert into coordinates(tag, color, time_begin, time_end, latitude_begin)
values('tag3', 'red', '2016-01-01T11:35:01', '2016-01-01T12:00:00', 13000);

insert into coordinates(tag, color, time_begin, time_end, latitude_begin)
values('tag3', 'red', '2016-01-01T12:00:00', '2016-01-01T12:00:11', 13001);

.headers on
.mode column

select * from coordinates where tag='tag1' and '2006-06-01T07:56:18' between time_begin and time_end;

select * from coordinates where color='blue' and time_end between '2014-03-13T00:00:00' and '2014-03-13T00:10:00';

输出:

sqlite> select * from coordinates where tag='tag1' and '2006-06-01T07:56:18' between time_begin and time_end;
id          tag         color       time_begin           time_end             latitude_begin
----------  ----------  ----------  -------------------  -------------------  --------------
1           tag1        green       2006-06-01T07:56:17  2006-06-01T07:56:19  123
sqlite>
sqlite> select * from coordinates where color='blue' and time_end between '2014-03-13T00:00:00' and '2014-03-13T00:10:00';
id          tag         color       time_begin           time_end             latitude_begin
----------  ----------  ----------  -------------------  -------------------  --------------
4           tag2        blue        2014-03-12T23:59:59  2014-03-13T00:00:29  2978