I have two models a parent and the son contains two float fields
one of the values this calculates according to the other but when I change the father how can be my calculating function.
Here is my example:
class A(models.model):
trv_ids = fields.One2many(classB,id_A)
class B(models.model):
id_A = fields.Many2one(classA)
qtite = fields.float(default=0)
qtite1 = fields.float(default=0,compute=?????)
qtite1 gets the value of qtite when I change parent
as the example of cumulated amount becomes previous quantity the next month.
Thanks
If i understood right i think what you need is something like this:
#api.depends('id_A')
def _compute_qtie1(self):
for record in self:
record.qtite1 = record.qtite
qtite1 = fields.float(compute=_compute_qtie1, store=True)
The depends is what triggers (any time you change the id_A field in the record) the compute method, if you dont store it in the DB it will re-calculate every time you open a view that contains the record.
Related
I have 4 model like this
class Site(models.Model):
name = models.CharField(max_length=200)
def get_lowest_price(self, mm_date):
'''This method returns lowest product price on a site at a particular date'''
class Category(models.Model):
name = models.CharField(max_length=200)
site = models.ForeignKey(Site)
class Product(models.Model):
name = models.CharField(max_length=200)
category = models.ForeignKey(Category)
class Price(models.Model):
date = models.DateField()
price = models.IntegerField()
product = models.ForeignKey(Product)
Here every have many category, every category have many product. Now product price can change every day so price model will hold the product price and date.
My problem is I want list of site filter by price range. This price range will depends on the get_lowest_price method and can be sort Min to Max and Max to Min. Already I've used lambda expression to do that but I think it's not appropriate
sorted(Site.objects.all(), key=lambda x: x.get_lowest_price(the_date))
Also I can get all site within a price range by running a loop but this is also not a good idea. Please help my someone to do the query in right manner.
If you still need more clear view of the question please see the first comment from "Ishtiaque Khan", his assumption is 100% right.
*In these models writing frequency is low and reading frequency is high.
1. Using query
If you just wanna query using a specific date. Here is how:
q = Site.objects.filter(category__product__price__date=mm_date) \
.annotate(min_price=Min('category__product__price__price')) \
.filter(min_price__gte=min_price, min_price__lte=max_price)
It will return a list of Site with lowest price on mm_date fall within range of min_price - max_price. You can also query for multiple date using query like so:
q = Site.objects.values('name', 'category__product__price__date') \
.annotate(min_price=Min('category__product__price__price')) \
.filter(min_price__gte=min_price, min_price__lte=max_price)
2. Eager/pre-calculation, you can use post_save signal. Since the write frequency is low this will not be expensive
Create another Table to hold lowest prices per date. Like this:
class LowestPrice(models.Model):
date = models.DateField()
site = models.ForeignKey(Site)
lowest_price = models.IntegerField(default=0)
Use post_save signal to calculate and update this every time there. Sample code (not tested)
from django.db.models.signals import post_save
from django.dispatch import receiver
#receiver(post_save, sender=Price)
def update_price(sender, instance, **kwargs):
cur_price = LowestPrice.objects.filter(site=instance.product.category.site, date=instance.date).first()
if not cur_price:
new_price = LowestPrice()
new_price.site = instance.product.category.site
new_price.date = instance.date
else:
new_price = cur_price
# update price only if needed
if instance.price<new_price.lowest_price:
new_price.lowest_price = instance.price
new_price.save()
Then just query directly from this table when needed:
LowestPrice.objects.filter(date=mm_date, lowest_price__gte=min_price, lowest_price__lte=max_price)
Solution:
from django.db.models import Min
Site.objects.annotate(
price_min=Min('categories__products__prices__price')
).filter(
categories__products__prices__date=the_date,
).distinct().order_by('price_min') # prefix '-' for descending order
For this to work, you need to modify the models by adding a related_name attribute to the ForeignKey fields.
Like this -
class Category(models.Model):
# rest of the fields
site = models.ForeignKey(Site, related_name='categories')
Similary, for Product and Price models, add related_name as products and prices in the ForeignKey fields.
Explanation:
Starting with related_name, it describes the reverse relation from one model to another.
After the reverse relationship is setup, you can use them to inner join the tables.
You can use the reverse relationships to get the price of a product of a category on a site and annotate the min price, filtered by the_date. I have used the annotated value to order by min price of the product, in ascending order. You can use '-' as a prefix character to do in descending order.
Do it with django queryset operations
Price.objects.all().order_by('price') #add [0] for only the first object
or
Price.objects.all().order_by('-price') #add [0] for only the first object
or
Price.objects.filter(date= ... ).order_by('price') #add [0] for only the first object
or
Price.objects.filter(date= ... ).order_by('-price') #add [0] for only the first object
or
Price.objects.filter(date= ... , price__gte=lower_limit, price__lte=upper_limit ).order_by('price') #add [0] for only the first object
or
Price.objects.filter(date= ... , price__gte=lower_limit, price__lte=upper_limit ).order_by('-price') #add [0] for only the first object
I think this ORM query could do the job ...
from django.db.models import Min
sites = Site.objects.annotate(price_min= Min('category__product__price'))
.filter(category__product__price=mm_date).unique().order_by('price_min')
or /and for reversing the order :
sites = Site.objects.annotate(price_min= Min('category__product__price'))
.filter(category__product__price=mm_date).unique().order_by('-price_min')
I'm new to web development and rails, and I'm trying to construct a query object for my first time. I have a table Players, and a table DefensiveStats, which has a foriegn-key player_id, so each row in this table belongs to a player. Players have a field api_player_number, which is an id used by a 3rd party that I'm referencing. A DefensiveStats object has two fields that are relevant for this query - a season_number integer and a week_number integer. What I'd like to do is build a single query that takes 3 parameters: an api_player_number, season_number, and week_number, and it should return the DefensiveStats object with the corresponding season and week numbers, that belongs to the player with api_player_number = passed in api_player_number.
Here is what I have attempted:
class DefensiveStatsWeekInSeasonQuery
def initialize(season_number, week_number, api_player_number)
#season_number = season_number
#week_number = week_number
#api_player_number = api_player_number
end
# data method always returns an object or list of object, not a relation
def data
defensive_stats = Player.where(api_player_number: #api_player_number)
.joins(:defensive_stats)
.where(season_number:#season_number, week_number: #week_number)
if defensive_stats.nil?
defensive_stats = DefensiveStats.new
end
defensive_stats
end
end
However, this does not work, as it performs the second where clause on the Player class, and not the DefensiveStats class -> specifically, "SQLite3::SQLException: no such column: players.season_number"
How can I construct this query? Thank you!!!
Player.joins(:defensive_stats).where(players: {api_player_number: #api_player_number}, defensive_stats: {season_number: #season_number, week_number: #week_number})
OR
Player.joins(:defensive_stats).where("players.api_player_number = ? and defensive_stats.season_number = ? and defensive_stats.week_number = ?", #api_player_number, #season_number, #week_number)
I am reading about DDD and I have learned that Value Object is immutable, if you want to change it, you will have to create a new one.
I have just read the information on How are Value Objects stored in the database? , it works well for Address class and I also read https://cargotracker.java.net/ and https://gojko.net/2009/09/30/ddd-and-relational-databases-the-value-object-dilemma/. But I want to do something different .
I am working on a billing system , it has 4 tables/classes
TPerson - fields: id_person, name -> <<Entity>>
TMobile - fields: id_mobile, number -> <<Entity>>
TPeriod - fields: id_period, id_person, id_mobile, begin_date, end_date -> <<Value Object>> (I think, because the dates can be change)
TCall - field: id_call, id_period, etc... -> <<Value Object>>
The table TCall has many records, if I change the period record dates (Value Object, table TPeriod) it will create another Object Period then id_period will change(delete, insert a record) , but the foreign key in table TCall will be violated. How Could I implement the period class ? if i implement as a value object , it will be immutable and turns out I will not be able to change anything whatsoever.
Thanks,
Fernando
if it's a value object you don't have a period table/id.
A value object is just a grouping of certain fields. For example a call might have a start time, an end time, and then you could create a Duration Value object with starttime and end time from the call table. In your java code it would be then more convenient to talk about the call duration instead of the start/end time separately.
However, it certainly could make sense to make period an entity, but then period 201601 probally always have the same start/end time and you wouldn't need to make changes to it. And if you did you make changes to the entity directly and keeping the ids in tact.
Thank for your help,
I have this situation:
TPerson - fields: id_person = 1 , name = "John"
TMobile - fields: id_mobile = 100, number "555-0123"
TPeriod - fields: id_period = 1000, id_person = 1 , id_mobile = 1, begin_date = "2016-01-01", end_date = "2049-12-31"
TCall - field: id_call = 1, id_period = 1000
The period is a relation between TPerson and TPeriod, in this example John has a mobile between "2016-01-01" and "2049-12-31". On the table TCall there are John's calls record, but if i replace the period (TPeriod table) end_date to "2016-02-01", from my understanding the end_date will be inconsistent, it turns out i cann't replace because it's a value object, not a entity. I considered to implement like this.
// Create a class DatePeriod
public class DatePeriod {
private final begin_date;
private final end_date;
DatePeriod() {}
public static DatePeriod of(Date begin_date, Date end_date) {
this.begin_date = begin_date;
this.end_date = end_date;
}
// implement equals / hashcode...
}
// Period class
public class Period {
int id;
// others mappings id_person / id_mobile
DatePeriod datePeriod;
}
Still, i will have to update datePeriod attribute
Thank you for your attention to this matter
I want to know how to show a one2many computed field in a tree view, I tried the following code but without results:
#api.one
def _compute_o2m_field(self):
related_recordset = self.env["product.product"].search([])
self.productos = related_recordset
products = fields.One2many(string="products", compute='_compute_o2m_field')
any idea?,
thanks
#api.one
def _compute_o2m_field(self):
related_recordset = self.env["product.product"].search([])
self.products = related_recordset.ids
products = fields.One2many('product.product','many2onefieldonproduct',string="products", compute='_compute_o2m_field')
Computed Fields
There is no more direct creation of fields.function.
Instead you add a compute kwarg. The value is the name of the function as a string or a function. This allows to
have fields definition atop of class
Your compute function should be like this,
#api.multi
def _compute_o2m_field(self):
related_recordset = self.env["product.product"].search([])
for obj in self:
obj.products = related_recordset
One2many
Store a relation against many rows of co-model.
Specific options:
• comodel_name: name of the opposite model
• comodel_name: relational column of the opposite model
So, your field definition should be like this,
products = fields.One2many(comodel_name,comodel_name,string="products", compute='_compute_o2m_field')
I want to join records together and separate them with "-"
I know how to join one table records together like this:
#keywords = #tweet.hash_tags.join("-")
But what if it's HABTM associated tables.
For example.
// BRAND MODEL
has_and_belongs_to_many :categories
// CATEGORY MODEL
has_and_belongs_to_many :brands
If I do this:
#brands = Brand.all
#brand_categories = #brands.categories.join("-")
I get this result:
#<Category:0x0000010445c928>,#<Category:0x0000010445c7c0>,#<Category:0x0000010445c5e0>,#<Category:0x0000010445c400>,#<Category:0x0000010445c270>
Hope you understand my question - thanks.
#join will call #to_s on the items in the Array returned by #brands.categories by default, and it doesn't look like you've defined a custom Category#to_s. Either do so, or be more explicit about the string representation you want; if, for example, a Category has a title attribute, you could use:
#brands_categories = #brands.categories.map(&:title).join("-")
Assuming your Category table has a name field:
#brand_categories = #brands.categories.collect(&:name).join("-")
This will put all of the name values into an array, and then join those.