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);
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'm performing some maintenance on some code that uses NHibernate as a person who knows almost nothing about NHibernate...
I have the following query
var query = string.Format(#"select s.Id, s.Iccid, c.Name as Carrier, aa.StartDate as AssignmentDate, cust.Name as AssignedCustomerName
from assetassignment aa
left join SIM s on aa.AssetId = s.Id
left join Carrier c on s.CarrierId = c.Id
left join customer cust on aa.CustomerId = cust.Id
where aa.enddate is null
and aa.CustomerId in ({0})
and s.dateremoved is null",
string.Join(",",idsToInclude));
if (!string.IsNullOrWhiteSpace(carrier))
{
query += " and c.Name = '" + carrier + "'";
}
var results = _session.CreateSQLQuery(query)
.SetResultTransformer(new AliasToBeanResultTransformer(typeof(HomepageSIMTableRow)))
.List<HomepageSIMTableRow>();
return results;
This works fine for me (and means I didn't have to grok NHibernate to get something running I could work against but now I need to add paging and it is just feeling smelly.
Any guidance on how to move this into NHibernate land and add paging would be awesome!
I'm not sure if this works with regular SQL, but usually with NHibernate you add a
var results = _session.CreateSQLQuery(query)
.SetFirstResult(0)
.SetSetMaxResults(30)
.SetResultTransformer(new AliasToBeanResultTransformer(typeof(HomepageSIMTableRow)))
.List<HomepageSIMTableRow>();
This works for regular Criterias and HQL queries.
You can read this as a reference: How can you do paging with NHibernate?
The reason this feels "smelly" is because you're writing SQL and passing it straight to the ORM.
NH offers a whole mechanism for paging at an entity level. I have found this to get a little tricky when you're eagerly loading other entities though.
My suggestion would be to either:
Write the pagination SQL yourself, this is probably lower risk as it will involve less changes
Convert the whole query to use NH ICriterion query or a HQL statement.
Unfortunately it's hard to suggest which one without knowing the risk/situation.
I have this SQL expression:
SELECT Musclegroups.Name, COUNT(DISTINCT Workouts.WorkoutID) AS Expr1
FROM Workouts INNER JOIN
Series ON Workouts.WorkoutID = Series.WorkoutID INNER JOIN
Exercises ON Series.ExerciseID = Exercises.ExerciseID INNER JOIN
Musclegroups ON Musclegroups.MusclegroupID = Exercises.MusclegroupID
GROUP BY Musclegroups.Name
Since Im working on a project which uses EF in a WCF Ria LinqToEntitiesDomainService, I have to query this with LINQ (If this isn't a must then pls inform me).
I made this expression:
var WorkoutCountPerMusclegroup = (from s in ObjectContext.Series1
join w in ObjectContext.Workouts on s.WorkoutID equals w.WorkoutID
where w.UserID.Equals(userid) && w.Type.Equals("WeightLifting")
group s by s.Exercise.Musclegroup into g
select new StringKeyIntValuePair
{
TestID = g.Select(n => n.Exercise.MusclegroupID).FirstOrDefault(),
Key = g.Select(n => n.Exercise.Musclegroup.Name).FirstOrDefault(),
Value = g.Select(n => n.WorkoutID).Distinct().Count()
});
The StringKeyIntValuePair is just a custom Entity type I made so I can send down the info to the Silverlight client. Also this is why I need to set an "TestID" for it, as it is an entity and it needs one.
And the problem is, that this linq query produces this horrible SQL statement:
http://pastebay.com/144532
I suppose there is a better way to query this information, a better linq expression maybe. Or is it possible to just query with plain SQL somehow?
EDIT:
I realized that the TestID is unnecessary because the other property named "Key" (the one on which Im grouping) becomes the key of the group, so it will be a key also. And after this, my query looks like this:
var WorkoutCountPerMusclegroup = (from s in ObjectContext.Series1
join w in ObjectContext.Workouts on s.WorkoutID equals w.WorkoutID
where w.UserID.Equals(userid) && w.Type.Equals("WeightLifting")
group w.WorkoutID by s.Exercise.Musclegroup.Name into g
select new StringKeyIntValuePair
{
Key = g.Key,
Value = g.Select(n => n).Distinct().Count()
});
This produces the following SQL: http://pastebay.com/144545
This seems far better then the previous sql statement of the half-baked linq query.
But is this good enough? Or this is the boundary of LinqToEntities capabilities, and if I want even more clear sql, I should make another DomainService which operates with LinqToSQL or something else?
Or the best way would be using a stored procedure, that returns Rowsets? If so, is there a best practice to do this asynchronously, like a simple WCF Ria DomainService query?
I would like to know best practices as well.
Compiling of lambda expression linq can take a lot of time (3–30s), especially using group by and then FirstOrDefault (for left inner joins meaning only taking values from the first row in the group).
The generated sql excecution might not be that bad but the compilation using DbContext which cannot be precompiled with .NET 4.0.
As an example 1 something like:
var q = from a in DbContext.A
join b ... into bb from b in bb.DefaultIfEmtpy()
group new { a, b } by new { ... } into g
select new
{
g.Key.Name1
g.Sum(p => p.b.Salary)
g.FirstOrDefault().b.SomeDate
};
Each FirstOrDefault we added in one case caused +2s compile time which added up 3 times = 6s only to compile not load data (which takes less than 500ms). This basically destroys your application's usability. The user will be waiting many times for no reason.
The only way we found so far to speed up the compilation is to mix lambda expression with object expression (might not be the correct notation).
Example 2: refactoring of previous example 1.
var q = (from a in DbContext.A
join b ... into bb from b in bb.DefaultIfEmtpy()
select new { a, b })
.GroupBy(p => new { ... })
.Select(g => new
{
g.Key.Name1
g.Sum(p => p.b.Salary)
g.FirstOrDefault().b.SomeDate
});
The above example did compile a lot faster than example 1 in our case but still not fast enough so the only solution for us in response-critical areas is to revert to native SQL (to Entities) or using views or stored procedures (in our case Oracle PL/SQL).
Once we have time we are going to test if precompilation works in .NET 4.5 and/or .NET 5.0 for DbContext.
Hope this helps and we can get other solutions.
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