在后台查询数据并在前台展示的场景中,当数据量较大时,页面加载会非常缓慢,此时建议使用后台分页查询的形式。在flask中,基于Flask-SQLAlchemy可以使用以下方式实现。
方法一:
Flask-SQLAlchemy 提供了一个 paginate()查询方法,参考:Flask 学习-73.Flask-SQLAlchemy 分页查询paginate_flasksqlalchemy分页查询_上海-悠悠的博客-CSDN博客
page4 = Server.query.paginate(page=4, per_page=2)
print(page4.items)
page3 = page4.prev()
print(page3.items)
查看源码:
def paginate(
self,
select: sa.sql.Select[t.Any],
*,
page: int | None = None,
per_page: int | None = None,
max_per_page: int | None = None,
error_out: bool = True,
count: bool = True,
) -> Pagination:
"""Apply an offset and limit to a select statment based on the current page and
number of items per page, returning a :class:`.Pagination` object.
The statement should select a model class, like ``select(User)``. This applies
``unique()`` and ``scalars()`` modifiers to the result, so compound selects will
not return the expected results.
:param select: The ``select`` statement to paginate.
:param page: The current page, used to calculate the offset. Defaults to the
``page`` query arg during a request, or 1 otherwise.
:param per_page: The maximum number of items on a page, used to calculate the
offset and limit. Defaults to the ``per_page`` query arg during a request,
or 20 otherwise.
:param max_per_page: The maximum allowed value for ``per_page``, to limit a
user-provided value. Use ``None`` for no limit. Defaults to 100.
:param error_out: Abort with a ``404 Not Found`` error if no items are returned
and ``page`` is not 1, or if ``page`` or ``per_page`` is less than 1, or if
either are not ints.
:param count: Calculate the total number of values by issuing an extra count
query. For very complex queries this may be inaccurate or slow, so it can be
disabled and set manually if necessary.
.. versionchanged:: 3.0
The ``count`` query is more efficient.
.. versionadded:: 3.0
"""
参数说明:
page: int,指定页码,从1开始
per_page: int,每一页显示几条数据
max_per_page:每页显示最大值当指定了max_per_page时,per_page会受到这个值的限制
error_out:是否抛出错误(默认为True)
count:是否计数,默认为True
返回值:
调用 paginate()查询方法会返回一个Pagination 对象的实例
Pagination类对象的属性主要有:
has_next:如果在目前页后至少还有一页的话,返回 True。
has_prev:如果在目前页之前至少还有一页的话,返回 True。
next_num:下一页的页面数。
prev_num:前一页的页面数。
另外还有如下的可调用方法:
iter_pages():一个迭代器,返回一个在分页导航中显示的页数列表。
prev():上一页的分页对象。
next():下一页的分页对象。
方法二:
利用限制查询方式手动实现分页,参考:Flask 查询,分页,排序及逻辑运算与聚合:_flask分页查询_Gray area的博客-CSDN博客
filters=[] # 组装通用查询过滤器filter,略
offset = (int(paging_start)-1)*int(paging_size)
data_qry = User.query.filter(and_(*filters)).offset(offset).limit(paging_size).all()
或者
data_qry = User.query.offset(offset).limit(paging_size).all()