Question

Group 1: SUPERSTORE
Group 2: BAUKHAM
Group 3: HILL
Group 4: NSW
Group 5: AUSTRALIA

多对多关系。
对于该记录中class PostTemplate(BaseModel): content = TextField(unique=True) class VkGroup(BaseModel): group_id = IntegerField(unique=True) class PostTemplateVkGroup(BaseModel): """ http://charlesleifer.com/blog/a-tour-of-tagging-schemas-many-to-many-bitmaps-and-more/ """ group = ForeignKeyField(VkGroup) post_template = ForeignKeyField(PostTemplate) def get_posted_templates_for_group(group_id: int) -> Iterable: """Get posted templates. Args: group_id (int): id группы """ queries = (PostTemplate .select() .join(PostTemplateVkGroups) .join(VkGroup) .where(VkGroup.group_id == group_id)) return queries all_post_templates = PostTemplate.select()中的每个记录，该记录中的帖子模板都用于该组中。

all_post_templates = not_posted_templates | posted_templates

我如何获得PostTemplateVkGroup？

Answer 1

如果您的数据库支持“ EXCEPT”操作，则可以：

all_post_templates = PostTemplate.alias().select()
post_templates = get_posted_templates_for_group(...)
difference = all_post_templates - post_templates

Sqlite示例：

class Post(Base):
    title = TextField()

class Tag(Base):
    tag = TextField()

class PostTag(Base):
    post = ForeignKeyField(Post)
    tag = ForeignKeyField(Tag)

db.create_tables([Post, Tag, PostTag])
data = (
    ('pa', ('ta1', 'ta2')),
    ('pb', ('tb1', 'tb2')),
    ('pc', ()))
for title, tags in data:
    post = Post.create(title=title)
    for tag in tags:
        tag = Tag.create(tag=tag)
        PostTag.create(post=post, tag=tag)

# Create some tags that aren't associated with any post.
Tag.create(tag='tx1')
Tag.create(tag='tx2')

pa1_tags = (Tag
            .select()
            .join(PostTag)
            .join(Post)
            .where(Post.title == 'pa'))
all_tags = Tag.alias().select()
diff = all_tags - pa1_tags
for t in diff:
    print(t.tag)

# Prints
# tb1
# tb2
# tx1
# tx2

如何获得不同的查询？

1 个答案: