I am trying to get the field value of a joined table. This is the generated sql of ORM query.
SELECTsubnets_subnetoption.id,
subnets_subnetoption.subnet_id,subnets_subnetoption.value_id,
subnets_subnet.id,subnets_subnet.parent_id,
subnets_subnet.base_address,subnets_subnet.bits,
subnets_subnet.bcast_address,subnets_subnet.is_physical,
subnets_subnet.name,subnets_subnet.responsible,
subnets_subnet.building_floor,subnets_subnet.comments,
subnets_subnet.vlan_common_name,subnets_subnet.creation_date,
subnets_subnet.modification_date,subnets_subnet.sec_level,
subnets_subnet.confid,subnets_subnet.access_type,
subnets_subnet.zone_type,options_value.id,
options_value.content,options_value.comment,
options_value.option_id,options_option.id,
options_option.name,options_option.required,
options_option.scope_id,options_scope.id,
options_scope.nameFROMsubnets_subnetoptionINNER JOIN
subnets_subnetON (subnets_subnetoption.subnet_id=
subnets_subnet.id) INNER JOINoptions_valueON
(subnets_subnetoption.value_id=options_value.id) INNER JOIN
options_optionON (options_value.option_id=
options_option.id) INNER JOINoptions_scopeON
(options_option.scope_id=options_scope.id) WHERE
subnets_subnetoption.subnet_id` = 1
SubnetOption.objects.select_related().filter(subnet_id=subnet['id']).query
I need only options_value.content and options_option.name, but query set i giving the subnetoption table values only. How can I get the joined tables values. I am new to django
SubnetOption.objects.filter(subnet_id=subnet['id']).select_related().values('options_value__content')
or
SubnetOption.objects.filter(subnet_id=subnet['id']).select_related('modelname_in_wholelowercase')
try this once
You can use raw query of django, which means you can put SQL query as it is, for reference
Raw sql queries in Django views
Related
With a raw query the columns for the SQL that will be executed can be accessed like this.
query_set = Model.objects.raw('select * from table')
query_set.columns
There is no columns attribute for django.db.models.query.QuerySet.
I'm not using raw ... I was debugging a normal query set using Q filters ... it was returning way too many records ... so I wrote code to see what the results would be with normal SQL. I'd like the see the columns and the actual SQL being called on a query set so I can diagnose what the issue is without guessing.
How do you get the columns or the SQL that will be executed from a django.db.models.query.QuerySet instance?
Ok, so based on your comment, if you want to see what django has created in terms of SQL there's an attribute you can use on the Queryset.
Once you've written your query, qs = MyModel.objects.all(), you can then inspect that by doing qs.query, which if you print that out will show you the SQL query itself.
You'll have to inspect this query to see what columns are being included.
The query object is a class called Query which I can't find mention of in the django docs, but it's source is here; https://github.com/django/django/blob/master/django/db/models/sql/query.py#L136
Currently I am developing website in Django & I need to convert some djnago query to sql equivalent query.
Purchase_order.objects.filter(query).order_by(id)[start: (start+length)]
I want to convert above django query into sql type of query.
Is there any way availble to convert it into sql also.
Yes. django does provides that feature. queryset comes with query object.
purchase_order = Purchase_order.objects.filter(query).order_by(id)[start: (start+length)]
print(purchase_order.query)
this will print corresponding query.
I writing a project using Django REST Framework, Django and Postgres as a database. I want to bulk delete in one query. So, it is possible to do without writing a query using pure SQL?
There is an example, but the count of executet query equal length of a list of ids (for example, if in delete_ids 2 ids, Django will execute 2 queries):
delete_ids = [...]
MyModel.objects.filter(id__in=delete_ids).delete()
Not possible using the filter and delete together using raw sql query.
https://docs.djangoproject.com/en/2.1/topics/db/sql/
MyModel.objects.raw('DELETE FROM my_model WHERE id IN (%s)', [','.join([list_of_ids])])
For fast deletes won't advice but you can also use
sql.DeleteQuery(MyModel).delete_qs(qs, using=qs.db)
jackotyne's answer is incorrect as a DELETE statement cannot be run with django raw. The idea behind django raw is that it returns a queryset, but DELETE won't do that.
Please read the reply to this answer.
You will need a database cursor as stated in the django documentation.
with connection.cursor() as cursor:
cursor.execute(
'DELETE FROM "appname_modelname" WHERE id IN (%s)' % ', '.join(delete_ids)
)
Of course it is better to filter with django and get a queryset and do a bulk delete with queryset.delete(), but that is not always possible depending on the data's logic.
In one of the django apps we use two database engine A and B, both are the same database but with different schemas. We have a table called C in both schemas but using db routing it's always made to point to database B. We have formed a valuelist queryset from one of the models in A, tried to pass the same in table C using filter condition __in but it always fetches empty though there are matching records. When we convert valueslist queryset to a list and use it in table C using filter condition __in it works fine.
Not working
data = modelindbA.objects.values_list('somecolumn',flat=True)
info = C.objects.filter(somecolumn__in=data).values_list
Working
data = modelindbA.objects.values_list('somecolumn',flat=True)
data = list(data)
info = C.objects.filter(somecolumn__in=data).values_list
I have read django docs and other SO questions, couldn't find anything relative. My guess is that since both models are in different database schemas the above is not working. I need assistance on how to troubleshoot this issue.
When you use a queryset with __in, Django will construct a single SQL query that uses a subquery for the __in clause. Since the two tables are in different databases, no rows will match.
By contrast, if you convert the first queryset to a list, Django will go ahead and fetch the data from the first database. When you then pass that data to the second query, hitting the second database, it will work as expected.
See the documentation for the in field lookup for more details:
You can also use a queryset to dynamically evaluate the list of values instead of providing a list of literal values.... This queryset will be evaluated as subselect statement:
SELECT ... WHERE blog.id IN (SELECT id FROM ... WHERE NAME LIKE '%Cheddar%')
Because values_list method returns django.db.models.query.QuerySet, not a list.
When you use it with same schema the orm optimise it and should make just one query, but when schemas are different it fails.
Just use list().
I would even recommend to use it for one schema since it can decrease complexity of query and work better on big tables.
Is it possible to prevent multiple querys when i use django ORM ? Example:
product = Product.objects.get(name="Banana")
for provider in product.providers.all():
print provider.name
This code will make 2 SQL querys:
1 - SELECT ••• FROM stock_product WHERE stock_product.name = 'Banana'
2 - SELECT stock_provider.id, stock_provider.name FROM stock_provider INNER JOIN stock_product_reference ON (stock_provider.id = stock_product_reference.provider_id) WHERE stock_product_reference.product_id = 1
I confess, i use Doctrine (PHP) for some projects. With doctrine it's possible to specify joins when retrieve the object (relations are populated in object, so no need to query database again for get attribute relation value).
Is it possible to do the same with Django's ORM ?
PS: I hop my question is comprehensive, english is not my primary language.
In Django 1.4 or later, you can use prefetch_related. It's like select_related but allows M2M relations and such.
product = Product.objects.prefetch_related('providers').get(name="Banana")
You still get two queries, though. From the docs:
prefetch_related, on the other hand, does a separate lookup for each relationship, and does the ‘joining’ in Python.
As for packing this down into a single query, Django won't do it like Doctrine because it doesn't do that much post-processing of the result set (Django would have to remove all the redundant column data, since you'll get a row per provider and each of these rows will have a copy of all of product's fields).
So if you want to pack this down to one query, you're going to have to turn it around and run the query on the Provider table (I'm guessing at your schema):
providers = Provider.objects.filter(product__name="Banana").select_related('product')
This should pack it down to one query, but you won't get a single product ORM object out of it, instead needing to get the product fields via providers[k].product.
You can use prefetch_related, sometimes in combination with select_related, to get all related objects in a single query: https://docs.djangoproject.com/en/1.5/ref/models/querysets/#prefetch-related