We need to join a single column from another table in a model. That attribute is named the same as one in the model itself, and as such needs to be renamed/aliased when joined on the model.
If the attribute on the model was the same, we could easily do a join:
def self.default_scope
joins("LEFT JOIN slugs ON slugs.type = 'shop' AND slugs.target = shops.id")
end
But since we only want the slugs.name attribute (renamed to slug), the only solution I've come up with so far, is this crazy scope:
def self.default_scope
select("shops.id AS id, shops.name AS name, […15 more…], slugs.name AS slug")
.joins("LEFT JOIN slugs ON slugs.type = 'shop' AND slugs.target = shops.id")
end
Is there any simpler ways to do this, or do we have to live with this abomination?
Try following
Replace select Statement
select("shops.id AS id, shops.name AS name, […15 more…], slugs.name AS slug")
With
select("shops.*, slugs.name AS slug")
Related
Using the Django ORM is it possible to perform a select_related (left join) with conditions additional to the default table1.id = table2.fk
Using the example models:
class Author(models.Model):
name = models.TextField()
age = models.IntegerField()
class Book(models.Model):
title = models.TextField()
and the raw sql
SELECT 'Book'.*, 'Author'.'name'
FROM 'Book'
LEFT JOIN
'Author'
ON 'Author'.'id' = 'Book'.'author_id'
AND 'Author'.'age' > 18 ;<---this line here is what id like to use via the ORM
I understand that in this simple example you can perform the filtering after the join, but that hasn't worked in my specific case. As i am doing sums across multiple left joins that require filters.
# gets all books which has author with age higher than 18
books = Book.objects.filter(author__age__gt=18)
returns queryset.
Then you can loop trough the queryset to access specific values and print them:
for b in books:
print(b.title, b.author.name, b.author.age)
I am looking for a perticular raw SQL query using Inner Join.
I have those models:
class EzMap(models.Model):
layers = models.ManyToManyField(Shapefile, verbose_name='Layers to display', null=True, blank=True)
class Shapefile(models.Model):
filename = models.CharField(max_length=255)
class Feature(models.Model):
shapefile = models.ForeignKey(Shapefile)
I would like to make a SQL Query valid with PostgreSQL that would be like this one:
select id from "table_feature" where' shapefile_ezmap_id = 1 ;
but I dont know how to use the INNER JOIN to filter features where the shapefile they belongs to are related to a particular ezmap object
Something like this:
try:
id = Feature.objects.get(shapefile__ezmap__id=1).id
except Feature.DoesNotExist:
id = 0 # or some other action when no result is found
You will need to use filter (instead of get) if you want to deal with multiple Feature results.
I have 2 models - Restaurant and Feature. They are connected via has_and_belongs_to_many relationship. The gist of it is that you have restaurants with many features like delivery, pizza, sandwiches, salad bar, vegetarian option,… So now when the user wants to filter the restaurants and lets say he checks pizza and delivery, I want to display all the restaurants that have both features; pizza, delivery and maybe some more, but it HAS TO HAVE pizza AND delivery.
If I do a simple .where('features IN (?)', params[:features]) I (of course) get the restaurants that have either - so or pizza or delivery or both - which is not at all what I want.
My SQL/Rails knowledge is kinda limited since I'm new to this but I asked a friend and now I have this huuuge SQL that gets the job done:
Restaurant.find_by_sql(['SELECT restaurant_id FROM (
SELECT features_restaurants.*, ROW_NUMBER() OVER(PARTITION BY restaurants.id ORDER BY features.id) AS rn FROM restaurants
JOIN features_restaurants ON restaurants.id = features_restaurants.restaurant_id
JOIN features ON features_restaurants.feature_id = features.id
WHERE features.id in (?)
) t
WHERE rn = ?', params[:features], params[:features].count])
So my question is: is there a better - more Rails even - way of doing this? How would you do it?
Oh BTW I'm using Rails 4 on Heroku so it's a Postgres DB.
This is an example of a set-iwthin-sets query. I advocate solving these with group by and having, because this provides a general framework.
Here is how this works in your case:
select fr.restaurant_id
from features_restaurants fr join
features f
on fr.feature_id = f.feature_id
group by fr.restaurant_id
having sum(case when f.feature_name = 'pizza' then 1 else 0 end) > 0 and
sum(case when f.feature_name = 'delivery' then 1 else 0 end) > 0
Each condition in the having clause is counting for the presence of one of the features -- "pizza" and "delivery". If both features are present, then you get the restaurant_id.
How much data is in your features table? Is it just a table of ids and names?
If so, and you're willing to do a little denormalization, you can do this much more easily by encoding the features as a text array on restaurant.
With this scheme your queries boil down to
select * from restaurants where restaurants.features #> ARRAY['pizza', 'delivery']
If you want to maintain your features table because it contains useful data, you can store the array of feature ids on the restaurant and do a query like this:
select * from restaurants where restaurants.feature_ids #> ARRAY[5, 17]
If you don't know the ids up front, and want it all in one query, you should be able to do something along these lines:
select * from restaurants where restaurants.feature_ids #> (
select id from features where name in ('pizza', 'delivery')
) as matched_features
That last query might need some more consideration...
Anyways, I've actually got a pretty detailed article written up about Tagging in Postgres and ActiveRecord if you want some more details.
This is not "copy and paste" solution but if you consider following steps you will have fast working query.
index feature_name column (I'm assuming that column feature_id is indexed on both tables)
place each feature_name param in exists():
select fr.restaurant_id
from
features_restaurants fr
where
exists(select true from features f where fr.feature_id = f.feature_id and f.feature_name = 'pizza')
and
exists(select true from features f where fr.feature_id = f.feature_id and f.feature_name = 'delivery')
group by
fr.restaurant_id
Maybe you're looking at it backwards?
Maybe try merging the restaurants returned by each feature.
Simplified:
pizza_restaurants = Feature.find_by_name('pizza').restaurants
delivery_restaurants = Feature.find_by_name('delivery').restaurants
pizza_delivery_restaurants = pizza_restaurants & delivery_restaurants
Obviously, this is a single instance solution. But it illustrates the idea.
UPDATE
Here's a dynamic method to pull in all filters without writing SQL (i.e. the "Railsy" way)
def get_restaurants_by_feature_names(features)
# accepts an array of feature names
restaurants = Restaurant.all
features.each do |f|
feature_restaurants = Feature.find_by_name(f).restaurants
restaurants = feature_restaurants & restaurants
end
return restaurants
end
Since its an AND condition (the OR conditions get dicey with AREL). I reread your stated problem and ignoring the SQL. I think this is what you want.
# in Restaurant
has_many :features
# in Feature
has_many :restaurants
# this is a contrived example. you may be doing something like
# where(name: 'pizza'). I'm just making this condition up. You
# could also make this more DRY by just passing in the name if
# that's what you're doing.
def self.pizza
where(pizza: true)
end
def self.delivery
where(delivery: true)
end
# query
Restaurant.features.pizza.delivery
Basically you call the association with ".features" and then you use the self methods defined on features. Hopefully I didn't misunderstand the original problem.
Cheers!
Restaurant
.joins(:features)
.where(features: {name: ['pizza','delivery']})
.group(:id)
.having('count(features.name) = ?', 2)
This seems to work for me. I tried it with SQLite though.
I have the following models (simplified):
class Category(models.model):
# ...
class Product(models.model):
# ...
class ProductCategory(models.Model):
product = models.ForeignKey(Product)
category = models.ForeignKey(Category)
# ...
class ProductImage(models.Model):
product = models.ForeignKey(Product)
image = models.ImageField(upload_to=product_image_path)
sort_order = models.PositiveIntegerField(default=100)
# ...
I want to construct a query that will get all the products associated with a particular category. I want to include just one of the many associated images--the image with the lowest sort_order--in the queryset so that a single query gets all of the data needed to show all products within a category.
In raw SQL I would might use a GROUP BY something like this:
SELECT * FROM catalog_product p
LEFT JOIN catalog_productcategory c ON (p.id = c.product_id)
LEFT JOIN catalog_productimage i ON (p.id = i.product_id)
WHERE c.category_id=2
GROUP BY p.id HAVING i.sort_order = MIN(sort_order)
Can this be done without using a raw query?
Edit - I should have noted what I've tried...
# inside Category model...
products = Product.objects.filter(productcategory__category=self) \
.annotate(Min('productimage__sort_order'))
While this query does GROUP BY, I do not see any way to (a) get the right ProductImage.image into the QuerySet eg. HAVING clause. I'm effectively trying to dynamically add a field to the Product instance (or the QuerySet) from a specific ProductImage instance. This may not be the way to do it with Django.
It isn't quite a raw query, but it isn't quite public api either.
You can add a group by clause to the queryset before it is evaluated:
qs = Product.objects.filter(some__foreign__key__join=something)
qs.group_by = 'some_field'
results = list(qs)
Word of caution, though: this behaves differently depending on the db backend.
catagory = Catagory.objects.get(get_your_catagory)
qs = Product.objects.annotate(Min('productimage__sortorder').filter(productcategory__category = catagory)
This should hit the DB only once, because querysets are lazy.
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.