python - Django:如何获取原始 SQL "COUNT(*)"查询的结果？

Question

我有一个关键字表，如下所示:

CREATE TABLE `keywords` ( 
    `keyword` VarChar( 48 ) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
    `id` Int( 11 ) AUTO_INCREMENT NOT NULL,
    `blog_posts_fulltext_count` Int( 11 ) NOT NULL,
    PRIMARY KEY ( `id` ) )

我还有一张博客文章表，如下所示:

CREATE TABLE `blog_posts` ( 
    `id` Int( 11 ) AUTO_INCREMENT NOT NULL,
    `title` LongText CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL,
    `summary` LongText CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL,
    PRIMARY KEY ( `id` ) );

CREATE FULLTEXT INDEX `title_summary_fulltext` ON `blog_posts`( `title`, `summary` );

如您所见，我在 blog_posts 中的 title、summary 字段上有一个全文索引。

以下搜索工作正常:

select count(*) from blog_posts where match(title,summary) against ('paid'); 

现在我想用 blog_posts 中 keyword 出现的行数填充字段 keywords.blog_posts_fulltext_count。

当我运行这个时:

keywords = Keywords.objects.all()
for the_keyword in keywords:
    query = "select count(id) from BlogPosts where match(title,summary) against ('{0}')".format(the_keyword.keyword)
    number_of_mentions = blog_posts.objects.raw(query)
    for obj in number_of_mentions:
        a = obj

...RawQuerySet number_of_mentions 似乎没有错误返回，number_of_mentions.query 包含:

 'select count(id) from blog_posts where match(title,summary) against ('paid')'

但是当代码运行 for obj in number_of_mentions 行时，它抛出:

raise InvalidQuery('Raw query must include the primary key')

我还尝试将查询字符串定义为:

query = "select count('id') from BlogPosts where match(title,summary) against ('{0}')".format(the_keyword.keyword)

...作为:

query = "select count(*) from BlogPosts where match(title,summary) against ('{0}')".format(the_keyword.keyword)

...产生相同的错误消息。

在 Django 中从原始 sql COUNT 命令获取结果的正确方法是什么？

Answer 1

当您使用 blog_posts.objects.raw() 时，Django 期望原始查询以某种方式返回 blog_posts 对象。但是您的计数查询将返回一个数字而不是一组对象。这就是您看到记录的 API here .

如果你想运行一个不会返回模型对象的查询，而是返回一些不同的东西(比如数字)，你必须使用同一页面的另一部分中描述的方法 — Executing custom SQL directly .

一般的想法是您必须使用游标(在数据库结果集上迭代的东西)并获得唯一的结果。以下示例应该可以让您了解如何执行此操作。

from django.db import connection

with connection.cursor() as cursor:
    cursor.execute("select count(id) from BlogPosts where match(title,summary) against (%s)", [the_keyword.keyword])
    # get a single line from the result
    row = cursor.fetchone()
    # get the value in the first column of the result (the only column)
    count_value = row[0]