class Country(Models.Model):
code = models.CharField(max_length=50)
name = models.CharField(max_length=500)
class Meta:
unique_together = (('code', 'name'),)
db_table = 'md_country'
class UserSettings(models.Model):
...
default_countries = models.ManyToManyField(Country, db_table='user_default_countries', related_name='default_countries')
I have two models inside django models, what im trying is when i add Country models to default_countries i want to preserve order. Currently when i append manytomany field django automatically sort by Country name (alphabetical order)
I have this code
# iterate one by one to preserve fetching order
country_models = [Country.objects.get(id=_id) for _id in request.data[default_countries]]
user_settings.default_countries.clear()
for c in country_models:
user_settings.default_countries.add(c)
After this when i inspect user_settings.default_countries i have ordered countries by name in alphabetical order.
I want to preserve when adding element. If i want to add France and Australia and i order the list like that i on the end when i pull data from db i want it to be ordered like that. Now on this example i have Australia then France.
EDIT:
I checked the database and when inserting the data, it insert in right order
For example if i want France(73) then Australia(13), France has smaller id so its inserted first. There is a problem with django when pulling the data from database.
So as I understand correct you want to sort by insert order:
someSetting = UserSettings.objects.first()
countries = someSetting.default_countries.order_by('id')
I found the workaround.
Firstly i defined new property inside model where default_countries is.
#property
def ordered_default_countries(self):
return self.default_countries.all().order_by('-id')
Then in serializer where i serialize this field i just pointed default_countries field to ordered_default_countries.
Related
I'm trying to understand how can I define model as a class containing 2 integers and 1 charfield and then make it a part of another model.
Example of data I need
I guess in object oriented programming I should define model class like this:
class Component(models.Model):
pipe_type = models.CharField(max_length=200)
length = models.IntegerField()
amount = models.IntegerField()
And then I don't know how can I use it with django models, it should be something like this:
class Item(models.Model):
name = models.CharField()
components_needed = ? LIST OF Component class ?
Also, since components needed size will wary for objects, it should be possible to extend it's size with button on a page, for example there could be 3 input fields and next to them would be "+" and "-" button to add/remove another set of 3 input fields
I spent entire day looking for solution, but at this point I'm not sure if django can handle this. I'm new to python and django, so there are many things I do not understand.
I will be grateful for any kind of help
the only way now( you canot put multi FK in one cell) is like django itself using with user/groups so you need 3 models.
in django there is group, user and user_group so i suggesting for you:
class Component(models.Model):
pipe_type = models.CharField(max_length=200)
length = models.IntegerField()
amount = models.IntegerField()
class Item(models.Model):
name = models.CharField()
class Item_Component(models.Model):
Component = models.ForeignKey(Component, on_delete=models.CASCADE)
Item = models.ForeignKey(Item, on_delete=models.CASCADE)
so now in third model you can have multiple rows with item and with diffrent component.
open yours db viewer app and see django user_group table.
I am looking for a way to retrieve a parent field during a query of the the children records. At this time I have the following example model.
class Record(models.Model):
event_title=models.CharField(max_length=500)
event_description=models.CharField(max_length=4000)
class SecondTable(models.Model):
event_code=models.ForeignKey(Record, default=0, on_delete=models.CASCADE)
wasfun=models.BoolField(default=True)
When I view the values of the queryset and select_related below, the values from the parent don't seem to be included (i.e. event_description). However, the .query property shows all the fields being selected.
SecondTable.objects.all().select_related("event_code").values()
Is there a way to see all values from the joined tables? Sorry for a newbie question. Thanks!
I think not in only one line, but you can try with next:
values_second_table = [s.name for s in SecondTable._meta.fields]
values_first_table = ['event_code__{}'.format(r.name) for r in Record._meta.fields]
my_values = values_second_table + values_first_table
SecondTable.objects.all().select_related("event_code").values(*my_values)
I have query that returns the following queryset:
results = <QuerySet [<Product: ItemA>, <Product: ItemA>, <Product: ItemB>, <Product: ItemB>, <Product: ItemB>, <Product: ItemC>, <Product: ItemC>]>
The __str__ representation of the model is name and each Product variation likely has a different value for the price field. After this query, I need to search my database for each Product in the queryset and return the lowest price for each unique name so like:
Lowest price for all in database where name is == to ItemA
Lowest price for all in database where name is == to ItemB
Lowest price for all in database where name is == to ItemC
I use the following block of code to accomplish this goal:
query_list = []
for each in results:
if each.name not in query_list: #Checks if the name of the object is not in in the query list
query_list.append(each.name) #Adds just the name of the objects so there is just one of each name in query_list
for each in query_list:
priced = results.filter(name=each).order_by('price').first() #Lowest price for each name in query_list
This feel very inefficient. Is there a way to make a similar computation without having to append the unique name of each Product to a separate list, and iterating over that list, and then making a query for each one? I feel like there is a way to use a type of complex lookup to accomplish my goals, maybe event use less Python, and make the db do more of the work, but the above is the best I've been able to figure out so far. There can be a lot of different hits in results so I need this block to be as efficient as possible
It is easy after reading docs Generating aggregates for each item in a QuerySet and also "Interaction with default ordering or order_by()".
from django.db.models import Min
prices = {x['name']: x['lowest_price']
for x in results.values('name').annotate(lowest_price=Min('price').order_by()}
for product in results:
if product.name in prices and product.price == prices[product.name]:
priced = row # output the row
del prices[product.name]
That runs by two database queries.
An even more efficient solution with one query is probably possible with Window function, but it requires an advanced database backend and it can't work e.g. in tests with sqlite3.
Ok
i have this class in my model :
i want to get the agencys value which is a many to many on this class and store them in a list or array . Agency which store agency_id with the id of my class on a seprate table.
Agency has it's own tabel as well
class GPSpecial(BaseModel):
hotel = models.ForeignKey('Hotel')
rooms = models.ManyToManyField('Room')
agencys = models.ManyToManyField('Agency')
You can make it a bit more compact by using the flat=True parameter:
agencys_spe = list(GPSpecial.objects.values_list('agencys', flat=True))
The list(..) part is not necessary: without it, you have a QuerySet that contains the ids, and the query is postponed. By using list(..) we force the data into a list (and the query is executed).
It is possible that multiple GPSpecial objects have a common Agency, in that case it will be repeated. We can use the .distinct() function to prevent that:
agencys_spe = list(GPSpecial.objects.values_list('agencys', flat=True).distinct())
If you are however interested in the Agency objects, for example of GPSpecials that satisfy a certain predicate, you better query the Agency objects directly, like for example:
agencies = Agency.objects.filter(gpspecial__is_active=True).distinct()
will produce all Agency objects for which a GPSpecial object exists where is_active is set to True.
I think i found the answer to my question:
agencys_sp = GPSpecial.objects.filter(agencys=32,is_active=True).values_list('agencys')
agencys_spe = [i[0] for i in agencys_sp]
I seem to be stuck on a classic ORM issue and don't know really how to handle it, so at this point any help is welcome.
Is there a way to get the pivot table on a hasManyThrough query? Better yet, apply some filter or sort to it. A typical example
Table products
id,title
Table categories
id,title
table products_categories
productsId, categoriesId, orderBy, main
So, in the above scenario, say you want to get all categories of product X that are (main = true) or you want to sort the the product categories by orderBy.
What happens now is a first SELECT on products to get the product data, a second SELECT on products_categories to get the categoriesId and a final SELECT on categories to get the actual categories. Ideally, filters and sort should be applied to the 2nd SELECT like
SELECT `id`,`productsId`,`categoriesId`,`orderBy`,`main` FROM `products_categories` WHERE `productsId` IN (180) WHERE main = 1 ORDER BY `orderBy` DESC
Another typical example would be wanting to order the product images based on the order the user wants them to
so you would have a products_images table
id,image,productsID,orderBy
and you would want to
SELECT from products_images WHERE productsId In (180) ORDER BY orderBy ASC
Is that even possible?
EDIT : Here is the relationship needed for an intermediate table to get what I need based on my schema.
Products.hasMany(Images,
{
as: "Images",
"foreignKey": "productsId",
"through": ProductsImagesItems,
scope: function (inst, filter) {
return {active: 1};
}
});
Thing is the scope function is giving me access to the final result and not to the intermediate table.
I am not sure to fully understand your problem(s), but for sure you need to move away from the table concept and express your problem in terms of Models and Relations.
The way I see it, you have two models Product(properties: title) and Category (properties: main).
Then, you can have relations between the two, potentially
Product belongsTo Category
Category hasMany Product
This means a product will belong to a single category, while a category may contain many products. There are other relations available
Then, using the generated REST API, you can filter GET requests to get items in function of their properties (like main in your case), or use custom GET requests (automatically generated when you add relations) to get for instance all products belonging to a specific category.
Does this helps ?
Based on what you have here I'd probably recommend using the scope option when defining the relationship. The LoopBack docs show a very similar example of the "product - category" scenario:
Product.hasMany(Category, {
as: 'categories',
scope: function(instance, filter) {
return { type: instance.type };
}
});
In the example above, instance is a category that is being matched, and each product would have a new categories property that would contain the matching Category entities for that Product. Note that this does not follow your exact data scheme, so you may need to play around with it. Also, I think your API query would have to specify that you want the categories related data loaded (those are not included by default):
/api/Products/13?filter{"include":["categories"]}
I suggest you define a custom / remote method in Product.js that does the work for you.
Product.getCategories(_productId){
// if you are taking product title as param instead of _productId,
// you will first need to find product ID
// then execute a find query on products_categories with
// 1. where filter to get only main categoris and productId = _productId
// 2. include filter to include product and category objects
// 3. orderBy filter to sort items based on orderBy column
// now you will get an array of products_categories.
// Each item / object in the array will have nested objects of Product and Category.
}