Django的LEFT JOIN - 一對多

我有以下型號：Django的LEFT JOIN - 一對多

class Employee(models.Model): 

    def getFullname(self): 
     return '{}, {} {}'.format(self.empLastname,self.empFirstname, self.empMiddlename) 

    empID = models.CharField(primary_key=True, max_length= 50, null=False) 
    empLastname = models.CharField(max_length=50) 
    empFirstname = models.CharField(max_length=50) 
    empMiddlename = models.CharField(max_length=50, null=True) 
    fullname = property(getFullname) 

    def __str__(self): 
     return self.fullname 

class Picture(models.Model): 
    empID = models.ForeignKey(Employee, related_name="pictures", to_field='empID', on_delete = models.CASCADE) 
    picture = models.ImageField('Uploaded image') 
    isDef = models.BooleanField(default=False)

我想查詢所有員工中的圖片模型isDefault=True。但並非所有員工都有照片。所以基本上我想查詢所有員工哪些isDefault=True和所有沒有圖片的員工。

我的查詢是這樣的：

SELECT manager_employee.`*`, manager_picture.* 
FROM manager_employee 
LEFT JOIN manager_picture ON (manager_employee.empID = manager_picture.empID_id 
AND manager_picture.isDef)

serializer.py

class PictureSerializer(serializers.ModelSerializer): 
     class Meta: 
      model = Picture 
      fields = (
        'empID', 
        'picture', 
        'isDef' 
      ) 

class EmployeeListSerializer(serializers.ModelSerializer): 
     pictures = PictureSerializer(many = True, read_only = True) 

     class Meta: 
      model = Employee 
      fields = (
        'empID', 
        'empLastname', 
        'empFirstname', 
        'empMiddlename', 
        'fullname', 
        'pictures' 
      )

該查詢給了我正確的結果。該問題是如何做到這一點的Django ..

假設我有員工記錄模型

 
============================================================================= 
empID | empLastname | empFirstname | empMiddlename | fullname  | 
============================================================================= 
    1  | Doe   | John   | Smith   | Doe, John Smith | 
----------------------------------------------------------------------------- 
    2  | Potter   | Harry   | Moon   | Potter, Harry ..| 
----------------------------------------------------------------------------- 
    3  | Aaaa   | Abbb   | Accc   | ...    | 
----------------------------------------------------------------------------- 
    4  | Baaaa   | Bbbb   | Bccc   | ...    | 
-----------------------------------------------------------------------------

現在在圖片模式

 
================================================ 
empID  | Picture     | isDef | 
================================================ 
    1  | Pic1.jpg     | 0  | 
------------------------------------------------ 
    1  | Pic2.jpg     | 0  | 
------------------------------------------------ 
    1  | Pic3.jpg     | 1  | *which makes this as default* 
------------------------------------------------ 
    2  | emp2Pic1.jpg    | 1  | *which makes this as default* 
------------------------------------------------ 
    2  | emp2Pic2.jpg    | 0  | 
------------------------------------------------ 
    4  | emp4Pic1.jpg    | 0  | 
------------------------------------------------ 
    4  | emp4Pic2.jpg    | 1  | *which makes this as default* 
------------------------------------------------

現在，當我嘗試這個SQL：

SELECT manager_employee.`*`, manager_picture.* 
    FROM manager_employee 
    LEFT JOIN manager_picture ON (manager_employee.empID = manager_picture.empID_id 
    AND manager_picture.isDefault)

這給我一個結果：

 
========================================================================= 
empID | empLastname | empFirstname | empMiddle | Picture  | isDef | 
1 | Doe   | John   | Smith  | Pic2.jpg  | 1  | 
2 | Potter  | Harry  | Moon  | emp2Pic1.jpg | 1  | 
3 | Aaaa  | Abbb   | Accc  | (null)  | (null) | 
4 | Baaaa  | Bbbb   | Bccc  | emp4Pic2.jpg | 1  | 
-------------------------------------------------------------------------

如何我在Django實現這一點？

請別人幫我.. TIA ..

來源

2016-11-21 N0LrAm

檢查這個http://stackoverflow.com/questions/21271835/left-join-django-orm –

@ PiyushS.Wanare我檢查的鏈接。但答案是LEFT OUTER JOIN而不是LEFT JOIN。當我測試答案，它沒有給我什麼.. – N0LrAm

'Picture.objects.filter（isDefault = True，picture__isnull = True）'這是你要找的嗎？這將爲您提供來自Picture模型的所有員工，其中isDefault = True且沒有圖片。 –

-1

Django的爲您提供的ORM，所以你不要有寫你的SQL。選中此項：Django queryset API reference。

此外，如果你想檢查你的Django查詢在SQL中的外觀。你可以嘗試像這樣在Django shell終端：

>>> queryset = MyModel.objects.all() 
>>> print queryset.query 
SELECT "myapp_mymodel"."id", ... FROM "myapp_mymodel"

來源

2016-11-21 07:16:18 Kishan

感謝您的答覆人..我沒有寫SQL ...我只是用它來檢查我的要求是否正確，這就是爲什麼我張貼示例查詢。唯一的問題是我不知道如何在Django中做到這一點。我知道ModelName.Objects.all（）看起來像「SELECT * FROM ModelName」..我不知道如何在Django中執行LEFT JOIN。希望你明白我的觀點..我的問題是views.py或serializers.py的樣子。 – N0LrAm

這不完全是你想要的 –

Django的LEFT JOIN - 一對多

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