how to write the sql bellow to django model sql language ?
select id,author_id from forum_node as answer_node where node_type='answer' and
'android' in (select tagnames from forum_node as question_node where
id=answer_node.parent_id );
could any one give help
Hard to say exactly without seeing you model classes, but selecting the relevant Forum_Node objects will look something like this:
Forum_Node.objects.filter(
node_type="answer",
parent__tagnames__name__in=['android']
)
Or, to get just the id and author_id:
Forum_Node.objects.filter(
node_type="answer",
parent__tagnames__name__in=['android']
).values_list('id', 'author_id')
Related
I have 3 Models: Offer, Request and Assignment. Assignment makes a connection between Request and Offer. Now I want to do this:
select *
from offer as a
where places > (
select count(*)
from assignment
where offer_id = a.id and
to_date > "2014-07-07");
I am not quiet sure how to achieve this with a django QuerySet... Any tips?
Edit: The query above is just an example, how the query in general should look like. The django model looks like this:
class Offer(models.Model):
...
places = models.IntegerField()
...
class Request(models.Model):
...
class Assignment(models.Model):
from_date = models.DateField()
to_data = models.DateField()
request = models.ForeignKey("Request",related_name="assignments")
offer = models.ForeignKey("Offer",related_name="assignments")
People now can create a offer with a given amount of places or a request. The admin then will connect a request with an offer for a given time. This is saved as an assignment. The query above should give me a list of offers, which have still places left. Therefore I want to count the number of valid assignments for a given offer to compare it with its number of places. This list should be used to find a possible offer for a given request to create a new assignment.
I hope this describes the problem better.
Unfortunately related subqueries aren't directly supported by ORM operations. Usage of .extra(where=...) should be possible in this case.
To get the same results without using a subquery something like the following should work:
Offer.objects.filter(
assignment__to_date__gt=thedate
).annotate(
assignment_cnt=Count('assignment')
).filter(
assignment_cnt__lte=F('places')
)
The exact query depends on the model definitions.
query = '''select *
from yourapp_offer as a
where places > (
select count(*)
from yourapp_assignment
where offer_id = a.id and
to_date > "2014-07-07");'''
offers = Offer.objects.raw(query):
https://docs.djangoproject.com/en/1.6/topics/db/sql/
I am new to entity framework and learning making queries. Can anyone please help me how can I convert the following SQL query to run in entity framework?
select max(isnull(TInvoice.InvoiceNr, 0)) + 1
from TInvoice inner join TOrders
on TInvoice.OrderId = TOrders.OrderId
where TOrders.ClientFirmId = 1
As comments have said, without the data model it is hard to be exact.
Would really need to see how you have defined your relations in your data model.
I guess from first read my first impression is something along the lines of:
int max = context.TInvoice.Where(x => x.TOrders.ClientFirmId == 1).Max(x => x.InvoiceNr);
I'm doing a rails app. I have to do a comparison engine a bit complex. I'm currently trying to do a prototype. My query can vary widely so i have to work with a lot of scopes, but that's not my problem.
My query have to compare candidates. These candidates have answered some tests. These tests belongs to category. Theses tests have different max value, and i have to be able to compare candidates by categories.
So i have to calculate a % of good answers. I have to be able to compare candidates in all possible use cases in one category. So, i have to be able to compare the average good answer rate for all this category.
In a nutshell : I have to be able to use subqueries in order to compare some candidates. I have to be able to compare them for a test or a category. My problem is using a subquery able to return a good answer rate for all tests a candidats may have passed in a category.
And I have to be able to use this subquery in an order_by or having clause.
How can I construct this subquery ? I have no problem to handle complex conditional queries with some scopes. This has to be a real subquery, because I am working with 6 or 7 models here.
I ask for an active record way, cause this must work with whatever database supported by rails.
Excuse my poor English.
Edit :
An example is worth 1000 words so how could do something like this :
Sessiontest.find(Candidat.where(:firstname => 'toto'))
This example is stupid, ok. So, is it possible to do something like this ?
Edit2 :
I saw some posts about AREL. I wish to know if it is possible to do this without a third party plugin.
Is it possible to do some sub queries in subqueries with arel? Because for example, my number of points per test, is the sum of the points of all his questions. (Sad, but I have to keep it). And I need this, so my subquery can calculate my good answers %.
So you got the idea. That's something, which has to be really powerful, so I need something powerful, and not too much error prone.
Edit3 : I made some progress, but I can't for a while post an answer.
It seem possible to get this work without any plugin. I have some success in buildings some subqueries like this :
toto = Candidat.where(:lastname => Candidat.select(:lastname).where(:lastname => "ulysse").limit(1))
The request :
Candidat Load (1.0ms)[0m SELECT "candidats".* FROM "candidats" WHERE "candidats"."lastname" IN (SELECT "candidats"."id" FROM "candidats" WHERE "candidats"."lastname" = 'ulysse' LIMIT 1
This works and create a real subquery. I will try some more advanced experiences, in order to get the level I actually need.
Just tried sub-subquery works wonder too.
Edit 5 :
I am trying some more advanced things, and there is a lot of things, i still don't understand.
- toto = Candidat.where("id = ? / ? ", Sessiontest.select(:id).where(:id => 6), Sessiontest.select(:id).where(:id => 2))
This is just a stupid example in order to get an object with an id of 3. This code works, but not as i expected.
See, the sql :
1m[35m (1.0ms)[0m SELECT COUNT("sessiontests"."id") FROM "sessiontests" WHERE "sessiontests"."id" = 6
[1m[36mSessiontest Load (0.0ms)[0m [1mSELECT id FROM "sessiontests" WHERE "sessiontests"."id" = 6[0m
[1m[35m (1.0ms)[0m SELECT COUNT("sessiontests"."id") FROM "sessiontests" WHERE "sessiontests"."id" = 2
[1m[36mSessiontest Load (1.0ms)[0m [1mSELECT id FROM "sessiontests" WHERE "sessiontests"."id" = 2[0m
[1m[35mCandidat Load (1.0ms)[0m SELECT "candidats".* FROM "candidats" WHERE (id = 6 / 2)
So, it does not use a subqueries. I tried with .to_sql. But it introduce my sql this way :
1m[36mCandidat Load (0.0ms)[0m [1mSELECT "candidats".* FROM "candidats" WHERE (id = 'SELECT id FROM "sessiontests" WHERE "sessiontests"."id" = 6' / 2 )[0m
So active record quoted the subreust for security purpose. this is closer to my wish, but not really what i want.
This does not work
Candidat.where("id = (?) / ? ", Sessiontest.select(:id).where(:id => 6).to_sql, Sessiontest.select(:id).where(:id => 2))
Quotes prevents the subquery to work.
But this work :
Candidat.where("id = (" + Sessiontest.select(:id).where(:id => 6).to_sql + ") / (" + Sessiontest.select(:id).where(:id => 2).to_sql + ") ")
[1m[36mCandidat Load (1.0ms)[0m [1mSELECT "candidats".* FROM "candidats" WHERE (id = (SELECT id FROM "sessiontests" WHERE "sessiontests"."id" = 6) / (SELECT id FROM "sessiontests" WHERE "sessiontests"."id" = 2) )[0m
But I find this ugly. I will try to get these subqueries working in a more dynamic way. I mean replace the integer values by columns name.
I don't have anymore the exact answer to this question, because i do not work in the same enterprise anymore. But the solution to this problem, was to use a group_by clause. So the request became really easy.
With a group_by, i was able to manipulate, category or a technology with ease.
I have a database table called Event which in CakePHP has its relationships coded to like so:
var $belongsTo = array('Sport');
var $hasOne = array('Result', 'Point', 'Writeup', 'Timetable', 'Photo');
Now am doing a query and only want to pull out Sport, Point, and Timetable
Which would result in me retrieving Sports, Events, Points, and Timetable.
Reason for not pulling everything is due the results having 17000+ rows.
Is there a way to only select those tables using:
$this->Event->find('all');
I have had a look at the API but can't see how its done.
You should set recursive to -1 in your app_model and only pull the things you require. never use recursive of 2 and http://book.cakephp.org/view/1323/Containable is awesome.
just $this->Event->find('all', array('contain' => array()));
if you do the trick of recursive as -1 in app_model, this is not needed, if would just be find('all') like you have
I have so category and this categories have unlimited sub category.
In Database Table, Fields are ID, UpperID and Title.
If I call a category and its subcategory in DataTable with recursive method in program(ASP.NET project)
performance is very bad.
And many user will use this application so everything goes bad.
Maybe All categories Fill to A Cache object and then we musnt go to Database.
But category count is 15000 or 20000.
So I think isn't a good method.
What can I do for fast performance?
Are you give me any suggestion?
caching or other in-memory-persistance is by far better than doing this on a relational system :) ... hey... it's oop!
just my 2 cents!
eg.
var categories = /* method for domain-objects*/.ToDictionary(category => category.ID);
foreach (var category in categories.Values)
{
if (!category.ParentCategoryID.HasValue)
{
continue;
}
Category parentCategory;
if (categories.TryGetValue(category.ParentCategoryID.Value, out parentCategory))
{
parentCategory.AddSubCategory(category);
}
}
et voila ... your tree is ready to go!
edit:
do you exactly know where your performance bottle-neck is?...
to give you some ideas, eg:
loading from database
building up the structure
querying the structure
loading from database:
then you should load it once and be sure to have some changetracking/notifying to get changes (if made) or optimize your query!
building up the structure:
the way i create the tree (traversal part) is the wastest you can do with a Dictionary<TKey, TValue>
querying the structure:
the structure i've used in my example is faster than List<T>. Dictionary<TKey, TValue> uses an index over the keys - so you may use int for the keys (IDs)
edit:
So you use DataTable to fix the
problem. Now you've got 2 problems: me
and DataTable
what do you have right now? where are you starting from? can you determine where your mudhole is? give us code!
Thanks All,
I find my solution with Common Table Expressions(CTE) fifty- fifty.
Its allow fast recursive queries.
WITH CatCTE(OID, Name, ParentID)
AS
(
SELECT OID, Name, ParentID FROM Work.dbo.eaCategory
WHERE OID = 0
UNION ALL
SELECT C.OID, C.Name, C.ParentID FROM Work.dbo.eaCategory C JOIN CatCTE as CTE ON C.ParentID= CTE.OID
)
SELECT * FROM CatCTE