I had tried to join two table conditionally but it is giving me syntax error. I tried to find solution in the net but i cannot find how to do conditional join with condition. The only other alternative is to get the value first from one table and make a query again.
I just want to confirm if there is any other way to do conditional join with linq.
Here is my code, I am trying to find all position that is equal or lower than me. Basically I want to get my peers and subordinates.
from e in entity.M_Employee
join p in entity.M_Position on e.PostionId >= p.PositionId
select p;
You can't do that with a LINQ joins - LINQ only supports equijoins. However, you can do this:
var query = from e in entity.M_Employee
from p in entity.M_Position
where e.PostionId >= p.PositionId
select p;
Or a slightly alternative but equivalent approach:
var query = entity.M_Employee
.SelectMany(e => entity.M_Position
.Where(p => e.PostionId >= p.PositionId));
Following:
from e in entity.M_Employee
from p in entity.M_Position.Where(p => e.PostionId >= p.PositionId)
select p;
will produce exactly the same SQL you are after (INNER JOIN Position P ON E..PostionId >= P.PositionId).
var currentDetails = from c in customers
group c by new { c.Name, c.Authed } into g
where g.Key.Authed == "True"
select g.OrderByDescending(t => t.EffectiveDate).First();
var currentAndUnauthorised = (from c in customers
join cd in currentDetails
on c.Name equals cd.Name
where c.EffectiveDate >= cd.EffectiveDate
select c).OrderBy(o => o.CoverId).ThenBy(o => o.EffectiveDate);
If you have a table of historic detail changes including authorisation status and effective date. The first query finds each customers current details and the second query adds all subsequent unauthorised detail changes in the table.
Hope this is helpful as it took me some time and help to get too.
Related
My project needs to let users build their own dynamic queries. From what I've read, Expression Trees are the way to go. However the syntax is rather complicated.
I envision having a GUI where users would be able to check tables, select columns, specify parameters,etc and then build a string such as:
var myQuery =
from P in context.Projects
join UA in context.UserAttributes on P.ProjectID equals UA.ProjectID
join UBA in context.UserBooleanAttributes on UA.UserAttributeID equals UBA.UserAttributeID
join U in context.Users on UBA.UserID equals U.UserID
where P.ProjectID == 1
where UBA.Value == true
where (UA.UserAttributeID == 1 || UA.UserAttributeID == 2)
select new { uba = U };
And store that in a queries table. To process the query, I was hoping there is some library out there that will magically do something like:
var result = magic(str);
foreach(var user in result)
Foo(user.Email);
In this example I know that all my queries would return Users, but for other queries I would probably have to use reflection or in another column specify the expected type in results.
I found one project called LinqTextQueryBuilder which looks interesting, but I wanted to see if there are other alternatives.
I'm having a bit trouble with a query in Linq to Entities which I hope someone can shed a light on :-) What I'm trying to do is to create a query that joins three tables.
So far it works, but since the last table I'm trying to join is empty, the result of the query doesn't contain any records. When I remove the last join, it gives me the right results.
My query looks like this:
var query = from p in db.QuizParticipants
join points in db.ParticipantPoints on p.id
equals points.participantId into participantsGroup
from po in participantsGroup
join winners in db.Winners on p.id
equals winners.participantId into winnersGroup
from w in winnersGroup
where p.hasAttended == 1 && p.weeknumber == weeknumber
select new
{
ParticipantId = p.id,
HasAttended = p.hasAttended,
Weeknumber = p.weeknumber,
UmbracoMemberId = p.umbMemberId,
Points = po.points,
HasWonFirstPrize = w.hasWonFirstPrize,
HasWonVoucher = w.hasWonVoucher
};
What I would like is to get some records even if the Winners table is empty or there is no match in it.
Any help/hint on this is greatly appreciated! :-)
Thanks a lot in advance.
/ Bo
If you set these up as related entities instead of doing joins, I think it will be easier to do what you're trying to do.
var query = from p in db.QuizParticipants
where p.hasAttended == 1 && p.weeknumber == weeknumber
select new
{
ParticipantId = p.id,
HasAttended = p.hasAttended,
Weeknumber = p.weeknumber,
UmbracoMemberId = p.umbMemberId,
Points = p.ParticipantPoints.Sum(pts => pts.points),
HasWonFirstPrize = p.Winners.Any(w => w.hasWonFirstPrize),
HasWonVoucher = p.Winners.Any(w => w.hasWonVoucher)
};
This is assuming hasWonFirstPrize and hasWonVoucher are boolean fields, but you can use any aggregate function to get the results you need, such as p.Winners.Any(w => w.hasWonFirstPrize == 1)
I don't use query syntax a lot but I believe you need to change from w in winnersGroup to from w in winnersGroup.DefaultIfEmpty()
I have the following query to start with:
var query = from p in db.Products
from pc in p.NpProductCategories
where pc.CategoryId == categoryId
select p;
I'm applying some more filtering on it and in the end I want to sort the results:
if (orderBy == ProductSortingEnum.Name)
query = query.OrderBy(x => x.Name);
else
query = query.OrderBy(............);
My big problem (coming from not knowing linq too good) is the ELSE here. How can I sort results by a column that is not in the current result set? I would like to somehow link to another linq query in the orderby. The sorting I'm trying to achive is to link to NpProductVariants query using the ProductId to match between NpProductVariant and Products
and sort by the Price of the NpProductVariant
Assuming you have the relationship set up in the dbml...
For one to one (and many to one):
query = query.OrderBy(p => p.NpProductVariant.Price);
For one to many:
query = query.OrderBy(p => p.NpProductVariants.Select(v => v.Price).Max());
Also:
var query =
from p in db.Products
where p.NpProductCategories.Any(pc => pc.CategoryId == categoryId)
select p;
I think you can hook your Join to your query as long as it is returning the same thing. So maybe something like (I'm not 100 % sure since I haven't tried it):
query = from i1 in query
join i2 in query2 on i1.PropertyToJoin equals i2.PropertyToJoin
orderby i1.OrderProp1, i2.OrderProp2
select i1;
But I think it might be a good idea to check the generated sql so it is still effective.
I wanted to do a paging style table, but NeerDinner example fetches the entire data into a PaggingList type, and I have more than 10 000 rows to be fetched, so I skipped that part.
so I come up with this query
var r = (from p in db.Prizes
join c in db.Calendars on p.calendar_id equals c.calendar_id
join ch in db.Challenges on c.calendar_id equals ch.calendar_id
join ca in db.ChallengeAnswers on ch.challenge_id equals ca.challenge_id
join cr in db.ChallengeResponses on ca.challenge_answer_id equals cr.challenge_answer_id
where
p.prize_id.Equals(prizeId)
&& ch.day >= p.from_day && ch.day <= p.to_day
&& ca.correct.Equals(true)
&& ch.day.Equals(day)
orderby cr.Subscribers.name
select new PossibleWinner()
{
Name = cr.Subscribers.name,
Email = cr.Subscribers.email,
SubscriberId = cr.subscriber_id,
ChallengeDay = ch.day,
Question = ch.question,
Answer = ca.answer
})
.Skip(size * page)
.Take(size);
Problem is, how can I get the total number of results before the Take part?
I was thinking of:
var t = (from p in db.JK_Prizes
join c in db.JK_Calendars on p.calendar_id equals c.calendar_id
join ch in db.JK_Challenges on c.calendar_id equals ch.calendar_id
join ca in db.JK_ChallengeAnswers on ch.challenge_id equals ca.challenge_id
join cr in db.JK_ChallengeResponses on ca.challenge_answer_id equals cr.challenge_answer_id
where
p.prize_id.Equals(prizeId)
&& ch.day >= p.from_day && ch.day <= p.to_day
&& ca.correct.Equals(true)
&& ch.day.Equals(day)
select cr.subscriber_id)
.Count();
but that will do the query all over again...
anyone has suggestions on how can I do this effectively ?
If you take a query as such:
var qry = (from x in y
select x).Count();
...LINQ to SQL will be clever enough to make this a SELECT COUNT query, which is potentially rather efficient (efficiency will depend more on the conditions in the query). Bottom line is that the count operation happens in the database, not in LINQ code.
Writing my old comments :Well i was facing the same issue some time back and then i came up with LINQ to SP =). Make an SP and drop that into your entities and use it.you can get write Sp according to your need like pulling total record column too. It is more easy and fast as compare to that whet you are using wright now.
You can put count for query logic as well as, see the sample as below:
public int GetTotalCountForAllEmployeesByReportsTo(int? reportsTo, string orderBy = default(string), int startRowIndex = default(int), int maximumRows = default(int))
{
//Validate Input
if (reportsTo.IsEmpty())
return GetTotalCountForAllEmployees(orderBy, startRowIndex, maximumRows);
return _DatabaseContext.Employees.Count(employee => reportsTo == null ? employee.ReportsTo == null : employee.ReportsTo == reportsTo);
}
I have some Linq code and it's working fine. It's a query that has a subquery in the Where clause. This subquery is doing a groupby. Works great.
The problem is that I don't know how to grab one of the results from the subquery out of the subquery into the parent.
Frst, here's the code. After that, I'll expplain what piece of data i'm wanting to extract.
var results = (from a in db.tblProducts
where (from r in db.tblReviews
where r.IdUserModified == 1
group r by
new
{
r.tblAddress.IdProductCode_Alpha,
r.tblAddress.IdProductCode_Beta,
r.tblAddress.IdProductCode_Gamma
}
into productGroup
orderby productGroup.Count() descending
select
new
{
productGroup.Key.IdProductCode_Alpha,
productGroup.Key.IdProductCode_Beta,
productGroup.Key.IdProductCode_Gamma,
ReviewCount = productGroup.Count()
}).Take(3)
.Any(
r =>
r.IdProductCode_Alpha== a.IdProductCode_Alpha&&
r.IdProductCode_Beta== a.IdProductCode_Beta&&
r.IdProductCode_Gamma== a.IdProductCode_Gamma)
where a.ProductFirstName == ""
select new {a.IdProduct, a.FullName}).ToList();
Ok. I've changed some field and tables names to protect the innocent. :)
See this last line :-
select new {a.IdProduct, a.FullName}).ToList();
I wish to include in that the ReviewCount (from the subquery). I'm jus not sure how.
To help understand the problem, this is what the data looks like.
Sub Query
IdProductCode_Alpha = 1, IdProductCode_Beta = 2, IdProductCode_Gamma = 3, ReviewCount = 10
... row 2 ...
... row 3 ...
Parent Query
IdProduct = 69, FullName = 'Jon Skeet's Wonder Balm'
So the subquery grabs the actual data i need. The parent query determines the correct product, based on the subquery filters.
EDIT 1: Schema
tblProducts
IdProductCode
FullName
ProductFirstName
tblReviews (each product has zero to many reviews)
IdProduct
IdProductCode_Alpha (can be null)
IdProductCode_Beta (can be null)
IdProductCode_Gamma (can be null)
IdPerson
So i'm trying to find the top 3 products a person has done reviews on.
The linq works perfectly... except i just don't know how to include the COUNT in the parent query (ie. pull that result from the subquery).
Cheers :)
Got it myself. Take note of the double from at the start of the query, then the Any() being replaced by a Where() clause.
var results = (from a in db.tblProducts
from g in (
from r in db.tblReviews
where r.IdUserModified == 1
group r by
new
{
r.tblAddress.IdProductCode_Alpha,
r.tblAddress.IdProductCode_Beta,
r.tblAddress.IdProductCode_Gamma
}
into productGroup
orderby productGroup.Count() descending
select
new
{
productGroup.Key.IdProductCode_Alpha,
productGroup.Key.IdProductCode_Beta,
productGroup.Key.IdProductCode_Gamma,
ReviewCount = productGroup.Count()
})
.Take(3)
Where(g.IdProductCode_Alpha== a.IdProductCode_Alpha&&
g.IdProductCode_Beta== a.IdProductCode_Beta&&
g.IdProductCode_Gamma== a.IdProductCode_Gamma)
where a.ProductFirstName == ""
select new {a.IdProduct, a.FullName, g.ReviewCount}).ToList();
While I don't understand LINQ completely, but wouldn't the JOIN work?
I know my answer doesn't help but it looks like you need a JOIN with the inner table(?).
I agree with shahkalpesh, both about the schema and the join.
You should be able to refactor...
r => r.IdProductCode_Alpha == a.IdProductCode_Alpha &&
r.IdProductCode_Beta == a.IdProductCode_Beta &&
r.IdProductCode_Gamma == a.IdProductCode_Gamma
into an inner join with tblProducts.