使用Python将JSON数组附加到另​​一个项目

Question

I recently migrated to Python and cannot solve quite simple problem (using Django). A model has JSON field (PostgreSQL), lets say, for example, fruits. When updating an instance, I do it like this:

model.fruits = {"id": 1, "name": "apple"}
model.save()

When editing a model, I would like to add another fruit (append), so the result would have few JSON items, and model.fruits would return value like this:

[
    {
        "id": 1,
        "name": "apple"
    },
    {
        "id": 2,
        "name": "banana"
    },
    {
        "id": 3,
        "name": "orange"
    },
]

I have tried to search for solutions, but it seems like append function for this dictionary overwrites the values, not appends them. What would be a fast way to append items to this JSON field in database? Maybe there is a library for fast work-around?

Answer 1

model.fruits = {"id": 1, "name": "apple"} * defines a dictionary, you cannot append to a dictionary, you can add keys to it

You can append elements into a JSON array though, eg if model.fruits was an array (or a list, as it is called in Python), eg

model.fruits = [{"id": 1, "name": "apple"},]

which defines an array with 1 element in it, then you can append to it

model.fruits.append({"id": 2, "name": "banana"})

Some references:

https://docs.djangoproject.com/en/1.8/ref/contrib/postgres/fields/#hstorefield https://docs.djangoproject.com/en/1.8/ref/contrib/postgres/fields/#arrayfield

_{* To be honest it doesn't make sense to name something in the plural like fruits to hold a single object, should be a container, like a list}

Answer 2

In Django, you should make a new model called Fruit.

class Fruit(models.Model):
    name = models.Charfield(max_length=50)

in your main model you should have a ManyToManyField .

fruits = models.ManyToManyField(Fruit, blank=True, related_name='model')

This way you would be able to add some more fields in future do filtering and whole other things.

To add a fruit to model object

obj.fruits.add(1, 2)  # where 1 and 2 are id's  of fruits to add