[英]How to get/filter the latest value of a field?
I have models as below: 我有以下模型:
class ProjectRecord(models.Model):
user = models.ForeignKey(User,on_delete=models.CASCADE, null=True, blank=True,related_name='user_projects')
project = models.ForeignKey(Project,on_delete=models.CASCADE, null=True, blank=True, related_name='user_projects')
project_type = models.CharField(max_length=30, choices=(("project_a","A"),("project_b","B")),null=True)
version = models.FloatField(null=True, blank=True)
I want to filter the latest value of version with this: 我想用这个过滤版本的最新值:
project = list(ProjectRecord.objects.filter(
user=self.request.user, project_type='project_a'
))
But I don't know how to achieve it.the data in database is similar as below: 但是我不知道如何实现。数据库中的数据如下所示:
id project_id version project_type
1 5 1.0 project_a
2 5 1.0 project_b
3 4 1.0 project_a
4 4 1.0 project_b
5 5 2.0 project_a
6 5 2.0 project_b
7 5 3.0 project_a
8 5 3.0 project_b
For example, I want to get the latest value of project_id=5
to exact match other data and do not delete other project_id
's value if their versions are not updated, the queryset
should be display as below 例如,我想获取
project_id=5
的最新值以与其他数据完全匹配,并且如果不更新其他project_id
的版本,则不要删除它们的值, queryset
应该显示如下
id project_id version project_type
1 4 1.0 project_a
2 4 1.0 project_b
3 5 3.0 project_a
4 5 3.0 project_b
Try to use annotation with Max
: 尝试对
Max
使用注释:
from django.db.models import Max
ProjectRecord.objects.filter(
user=self.request.user,
project_type='project_a'
).values(
'project_id', 'project_type'
).annotate(
max_version=Max('version')
)
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