Django ORM中使用update_or_create功能

官網的手寫版如下：

update_or_create( defaults=None,  **kwargs) ¶

A convenience method for updating an object with the given kwargs, creating a new one if necessary. The defaults is a dictionary of (field, value) pairs used to update the object. The values in defaults can be callables.

Returns a tuple of (object, created), where object is the created or updated object and created is a boolean specifying whether a new object was created.

The update_or_create method tries to fetch an object from database based on the given kwargs. If a match is found, it updates the fields passed in the defaults dictionary.

This is meant as a shortcut to boilerplatish code. For example:

大致意思是創建或者更新，當過濾條件匹配到查詢結果則將更新defaults字典中的字段，否則創建一條記錄，字段內容為defaults字段中的內容。

 返回（對象，已創建）的元組，其中object是已創建或已更新的對象，created是一個布爾值，指定是否創建了新對象。

defaults = {'first_name': 'Bob'}
try:
    obj = Person.objects.get(first_name='John', last_name='Lennon')
    for key, value in defaults.items():
        setattr(obj, key, value)
    obj.save()
except Person.DoesNotExist:
    new_values = {'first_name': 'John', 'last_name': 'Lennon'}
    new_values.update(defaults)
    obj = Person(**new_values)
    obj.save()

以上的方法使用update_or_create實現

obj, created = Person.objects.update_or_create(
    first_name='John', last_name='Lennon',
    defaults={'first_name': 'Bob'},
)