Django：如何从不同的模型中获取最新的对象？

Question

我正在尝试显示以下输出，其中 Cylinder、Issue 和 Return 是不同的模型，我期望的视图是圆柱表，其中仅显示最近创建的 issue 和 return 条目， 例如：

cylinderId=100 在 issue 表和 return 表中有两个条目，但在柱面表中只有最近创建的出现：-

cyId |   createdAt |  issuedDate  | username  | ReturnDate

100  |   5may,13:00|  6may,14:00  | anyone    | 7may,15:00

这里是模型：-

class Cylinder(models.Model):
    stachoice=[
    ('Fill','fill'),
    ('Empty','empty') 
    ]
    substachoice=[
    ('Available','available'), 
    ('Unavailable','unavailable'),
    ('Issued','issued') 
    
    ]
    cylinderId=models.CharField(max_length=50,primary_key=True,null=False)
    gasName=models.CharField(max_length=200)
    cylinderSize=models.CharField(max_length=30)
    Status=models.CharField(max_length=40,choices=stachoice,default='fill')
    Availability=models.CharField(max_length=40,choices=substachoice,default="Available")
    EntryDate=models.DateTimeField(default=timezone.now)
    
    

    def get_absolute_url(self):
        return reverse('cylinderDetail',args=[(self.cylinderId)])

    def __str__(self):
        return str(self.cylinderId)

class Issue(models.Model):
    cylinder=models.ForeignKey('Cylinder',on_delete=models.CASCADE)
    userName=models.CharField(max_length=60,null=False)
    issueDate=models.DateTimeField(default=timezone.now)
    
    def save(self,*args,**kwargs):
        if not self.pk: 
            if self.cylinder.Availability=='Available':
                Cylinder.objects.filter(cylinderId=self.cylinder.cylinderId).update(Availability=('Issued'))

        super().save(*args,**kwargs)
        
    def __str__(self):
        
        return str(self.userName) 


class Return(models.Model):
    fill=[
    ('Fill','fill'),
    ('Empty','empty'),
    ('refill','Refill')
    ]

    ava=[
    ('yes','YES'),
    ('no','NO')
    ]
    cylinder=models.ForeignKey('Cylinder',on_delete=models.CASCADE)
    availability=models.CharField(max_length=20,choices=ava)
    status=models.CharField(max_length=10,choices=fill)
    returnDate=models.DateTimeField(default=timezone.now)
    def save(self,*args,**kwargs):
        if not self.pk:

            if self.cylinder.Availability=='Issued':
                
                if self.availability=='YES' or self.availability=='yes':
                    Cylinder.objects.filter(cylinderId=self.cylinder.cylinderId).update(Availability='Available')
                    if self.status=='empty' or self.status=='Empty':
                        Cylinder.objects.filter(cylinderId=self.cylinder.cylinderId).update(Status='Empty')
                else:
                    Cylinder.objects.filter(cylinderId=self.cylinder.cylinderId).update(Availability='Unavailable')
                    if self.status=='refill' or self.status=='Refill':
                        Cylinder.objects.filter(cylinderId=self.cylinder.cylinderId).update(Status='Refill')
                    if self.status=='empty' or self.status=='Empty':
                        Cylinder.objects.filter(cylinderId=self.cylinder.cylinderId).update(Status='Empty')


        super().save(*args,**kwargs)

    def __str__(self):
        return str(self.cylinder)

查看：-

def cylinderListView(request):
    
    cylinder=Cylinder.objects.pefetch_related().order_by('-EntryDate')
    
    return render(request,'entry/cylinderList.html',locals())

模板圆柱列表.html:-

{%for cy in cylinder %}
                    <tr bgcolor="#e6f0ff" align="center">
                        
                    <td align="center" height="10" 
                width="50"><a style="border-width: 0px" href="{{cy.get_absolute_url}}">{{cy.cylinderId}}<a></td>
               
                    <td align="center" height="10" 
                width="50">{{cy.EntryDate}}</td>
                    <td align="center" height="10" 
                width="50">{{cy.gasName}}</td>
                <td align="center" height="10" 
                width="50">
                    {{cy.cylinderSize}}</td>
                    <td align="center" height="10" 
                width="50">
                    {{cy.Status}}</td>
                    <td align="center" height="10" 
                width="50">{{cy.Availability}}</td>

               
                {% if cy.issue_set.all%}
                
                {% for issue in cy.issue_set.all %}

               
                <td align="center" height="10" 
                width="50">{{issue.issueDate}}</td>
                <td align="center" height="10" 
                width="50">{{issue.userName}}</td>
                
               {% endfor %}
                
                {% else %}
                <td align="center" height="10" 
                width="50">-</td>
                <td align="center" height="10" 
                width="50">-</td>

                {% endif%}


                 {% if cy.return_set.all%}
                
                {% for return in cy.return_set.all %}
                
                <td align="center" height="10" 
                width="50">{{return.returnDate}}</td>
              
               {% endfor %}
                
                {% else %}
                
                <td align="center" height="10" 
                width="50">-</td>

                {% endif%}


                                    
                
                    </tr>

                    {% endfor %}
                </tbody>

            {% else %}

这是我期待的视图：-

对于这个结果我该怎么办？请帮忙:)

Answer 1

你可以使用latest()方法

Cylinder.objects.latest('EntryDate')

这将根据 CreatedAt 字段返回表中最新的 Cylinder 对象。

如果您想列出最新的气缸，请使用

Cylinder.objects.all().order_by('-EntryDate')    

Answer 2

只需将它们查询为Cylinder.objects.order_by('-pk')