Flask 学习-73.Flask-SQLAlchemy 分页查询paginate

Posted 2022-09-26 上海-悠悠

前言

Flask-SQLAlchemy 提供了一个分页查询方法 paginate（），方便我们实现在后端查询分页。

分页查询

在django 框架里面有个rest_framework.pagination 分页器, 只需简单的配置就可以实现分页

from rest_framework.pagination import PageNumberPagination

# 定义分页器简单分页(PageNumberPagination)
class MyPageNumberPagination(PageNumberPagination):
    page_size = 50                   # 默认每页显示的多少条记录
    page_query_param = 'page'         # 默认查询参数名为 page
    page_size_query_param = 'size'    # 前台控制每页显示的最大条数
    max_page_size = 100              # 后台控制显示的最大记录条数

Flask-SQLAlchemy 也提供了一个 paginate（）查询方法, 相关源码如下

    def paginate(self, page=None, per_page=None, error_out=True, max_per_page=None):
        """Returns ``per_page`` items from page ``page``.

        If ``page`` or ``per_page`` are ``None``, they will be retrieved from
        the request query. If ``max_per_page`` is specified, ``per_page`` will
        be limited to that value. If there is no request or they aren't in the
        query, they default to 1 and 20 respectively.

        When ``error_out`` is ``True`` (default), the following rules will
        cause a 404 response:

        * No items are found and ``page`` is not 1.
        * ``page`` is less than 1, or ``per_page`` is negative.
        * ``page`` or ``per_page`` are not ints.

        When ``error_out`` is ``False``, ``page`` and ``per_page`` default to
        1 and 20 respectively.

        Returns a :class:`Pagination` object.
        """

        return Pagination(self, page, per_page, total, items)

参数说明：
page： 指定页码，从1开始
per_page： 每一页显示几条数据
error_out：是否抛出错误（默认为True）大部分error_out 是False, page and per_page 默认值是 1和20
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

调用 paginate（）查询方法会返回一个Pagination 对象的实例

class Pagination(object):
    """Internal helper class returned by :meth:`BaseQuery.paginate`.  You
    can also construct it from any other SQLAlchemy query object if you are
    working with other libraries.  Additionally it is possible to pass `None`
    as query object in which case the :meth:`prev` and :meth:`next` will
    no longer work.
    """

    def __init__(self, query, page, per_page, total, items):
        #: the unlimited query object that was used to create this
        #: pagination object.
        self.query = query
        #: the current page number (1 indexed)
        self.page = page
        #: the number of items to be displayed on a page.
        self.per_page = per_page
        #: the total number of items matching the query
        self.total = total
        #: the items for the current page
        self.items = items

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。

实例属性有
query：创建Pagination对象对应的query对象
total：匹配的元素总数
per_page：每一页显示的元素个数
items：当前页面的查询结果

分页查询接口

from flask import make_response, request
from http import HTTPStatus

@api.route('/demo')
class ProjectInfoView(Resource):


    @api.doc(description='查询')
    @api.marshal_with(project_model)
    def get(self):
        """查询全部"""
        api.logger.info(f"GET query查询参数: request.args")
        # 按id倒序
        objs = Demo.query.order_by(Demo.id.desc())
        # 分页 page=None, per_page=None, error_out=True, max_per_page=None
        page_objs = objs.paginate(
            page=int(request.args.get("page", 1)),
            per_page=int(request.args.get("size", 10)),
            error_out=False,
            max_per_page=50
        ).items
        return page_objs, HTTPStatus.OK

分页接口查询示例/demo?page=1&size=3