Develop Reference

Optional condition in join clause - Linq

I have below linq query
var resultGuardian = from s in _db.Students
join sg in _db.StudentGuardians on s.StudentID equals sg.StudentID
join g in _db.Guardians on sg.GuardianId equals g.GuardianId
join lr in _db.luRelationTypes on sg.RelationTypeID equals lr.RelationTypeID
join ga in _db.GuardianAddresses on g.GuardianId equals ga.GuardianId
join ad in _db.Addresses on ga.AddressID equals ad.AddressID
join lt in _db.luAddressTypes on ad.AddressTypeID equals lt.AddressTypeID
join lg in _db.luGenders on g.GenderID equals (int?)lg.GenderID into ssts
from gdnr in ssts.DefaultIfEmpty()
where
s.TenantID == tenantid && sg.TenantID == tenantid && g.TenantID == tenantid &&
s.StatusId == (int?)Extension.StatusType.Active //1
&& g.StatusID == (int?)Extension.StatusType.Active &&
lr.StatusID == (int?)Extension.StatusType.Active && lr.TenantID == tenantid &&
s.StudentID == sid
select new
{
g.FirstName,
g.LastName,
IsPrimary = sg.IsPrimaryGuardian,
g.Education,
g.Email,
g.Phone,
lr.RelationCD,
ga.IsStudentAddress,
gdnr.GenderCD,
lt.AddressName,
ad.Address1,
ad.Address2,
ad.City,
ad.State,
ad.Zipcode
};
In above query when ad.AddressTypeID is null, it is not returning any result.
I have requirement if ad.AddressTypeID is null,than from LuAddressTypes fetch default record where AddressTypeCd=1. If I try this way
join lt in LuAddressTypes on ad.AddressTypeID equals lt.AddressTypeID into v1
from v2 in v1.DefaultIfEmpty()
select new
{
v2.AddressName,
g.Phone,..
});
in result v2.AddressName always returning null. I am unable to specify AddressTypeCd=1 where condition as well. AddressTypeCd=1 is not ad.AddressTypeID.
I need v2.AddressName where AddressTypeCd=1. How can I do that?
Find related entities all related entities

You can't use the standard LINQ join, but in LINQ to Entities you could use the alternative join syntax based on correlated Where - EF is smart enough to translate it to JOIN.
In your case, instead of
join lt in _db.luAddressTypes on ad.AddressTypeID equals lt.AddressTypeID
you could use
from lt in _db.luAddressTypes.Where(lt => ad.AddressTypeID == lt.AddressTypeID
|| (ad.AddressTypeID == null && lt.AddressTypeCd == 1))
which is translated to something like this
INNER JOIN [dbo].[LuAddressTypes] AS [Extent3]
ON ([Extent2].[AddressTypeID] = [Extent3].[AddressTypeID])
OR (([Extent2].[AddressTypeID] IS NULL) AND (1 = [Extent3].[AddressTypeCd]))
If you want LEFT OUTER JOIN, simply add .DefaultIfEmpty() at the end of the above line.

how to access table from embedded where LINQ c#

Please note below is entirely made up for example sake. I have a similar query based on an sql code but couldn't translate it to LINQ to get correct value.
The sql basically looks like this:
select * from customers c
join proucts p on c.id = p.customerid
join credit r on r.customerid=c.id and ISNULL(r.trandate, c.registeredDate) >= c.registeredDate
I also tried to tweak the above sql and put the condition inside where and it also returns the same value I am getting in my #2 LINQ below(which is incorrect).
How can I use c (customer) inside .Where of credit? see code
1.
from c in customers
join p in products on c.id = p.customerid
join cr in credit.Where(r=> r.tranDate => c.registeredDate!=null?c.registeredDate : r.purchaseDate) on c.id=cr.customerid
...
2.
I know you would suggest why not just put it in a where below like below but I am getting incorrect value.
from c in customers
join p in products on c.id = p.customerid
join cr in credit on c.id=cr.customerid
where r.tranDate => c.registeredDate!=null?c.registeredDate : r.purchaseDate
Is there a workaround? I have tried tons of others but won't get me the correct one.

LINQ supports only equijoins. Any additional criteria should go to where clause. And yes, the other range variables are inaccessible from the join inner sequence, so the filtering should happen before or after the join.
So this SQL query:
select * from customers c
join products p on c.id = p.customerid
join credit r on r.customerid = c.id
and ISNULL(r.trandate, c.registeredDate) >= c.registeredDate
directly translates to this LINQ query:
from c in customers
join p in products on c.id equals p.customerid
join cr in credit on c.id equals cr.customerid
where (cr.tranDate ?? c.registeredDate) >= c.registeredDate
select new { c, p, cr };
Optionally, the condition
(cr.tranDate ?? c.registeredDate) >= c.registeredDate
can be replaced with
(cr.tranDate == null || cr.tranDate >= c.registeredDate)

Return navigation property within join query

In building a patient appointment application I need to return patients with its navigation property patientDetails while those returned match a sessionId that is not directly deduced from the patient but rather from a series of other navigation properties. This in itself is not difficult, like plain SQL joins can be used, it's just that my navigation property patientDetails is never included.
The include path is correct, in case anyone asks.
using (DbEntities db = new DbEntities())
{
List<tblPatient> res = (from s in db.tblSessions
join b in db.tblBookings on s.id equals b.sessionId
join r in db.tblReferrals on b.referralId equals r.id
join a in db.tblAttendanceStatus on b.attendanceStatus equals a.id
join p in db.tblPatients.Include("tblPatientDetail") on r.patientId equals p.id
join pd in db.tblPatientDetails on p.patientDetailsId equals pd.id
where s.id == id
select p).ToList();
return res;
}
It appears to make no difference whether or not I include the .include.
What have I overlooked?

Includes are ignored when you use join or group by. You can change your query to use where instead
List<tblPatient> res = (from p in db.tblPatients.Include("tblPatientDetail")
where
(from s in db.tblSessions
join b in db.tblBookings on s.id equals b.sessionId
join r in db.tblReferrals on b.referralId equals r.id
join a in db.tblAttendanceStatus on b.attendanceStatus equals a.id
where r.patientId == p.id
where s.id == id
select 1).Any()
select p).ToList()

LINQ Join not returning results if second or third table empty

I've three tables :
Module_Articles_Articles
Module_Articles_Categories
Module_Articles_Comments
and I want to display my articles in repeater my query :
var articles =
(from a in context.Module_Articles_Articles
join c in context.Module_Articles_Categories on a.CategoryID equals c.CategoryID
join co in context.Module_Articles_Comments on a.ArticleID equals co.ArticleID
where a.IsDraft == false
orderby a.ArticleID descending
select new
{
a.ArticleID,
a.ArticleTitle,
a.ArticleContent,
a.Image,
a.Sender,
a.SentDate,
a.Summary,
a.Likes,
a.Dislikes,
a.Tags,
a.PostMode,
c.CategoryID,
c.CategoryTitle,
AcceptedCommentsCount =
(from com in context.Module_Articles_Comments where com.ArticleID == a.ArticleID && com.Status select com)
.Count(),
DeniedCommentsCount =
(from com in context.Module_Articles_Comments where com.ArticleID == a.ArticleID
&& com.Status == false select com)
.Count()
}).ToList();
but when Module_Articles_Categories or Module_Articles_Comments are empty my query returns nothing!
Is my code true? If not, how can I do this?

you want an OUTTER JOIN, which can be accomplished in a query like this by simply adding .DefaultIfEmpty()
from a in context.Module_Articles_Articles
join c in context.Module_Articles_Categories on a.CategoryID equals c.CategoryID into ca
from c in cs.DefaultIfEmpty()
join co in context.Module_Articles_Comments on a.ArticleID equals co.ArticleID into com
from co in com.DefaultIfEmpty()
where a.IsDraft == false
orderby a.ArticleID descending
select new ...

You are not getting results because your LINQ joins result in INNER JOINs. You probably want LEFT JOINs. Do it as follows.
var articles =
(from a in context.Module_Articles_Articles
join c in context.Module_Articles_Categories on a.CategoryID equals c.CategoryID into joinTable1
from c in joinTable1.DefaultIfEmpty()
join co in context.Module_Articles_Comments on a.ArticleID equals co.ArticleID into joinTable2
from co in joinTable2.DefaultIfEmpty()
where a.IsDraft == false
orderby a.ArticleID descending
select new
{
a.ArticleID,
a.ArticleTitle,
a.ArticleContent,
a.Image,
a.Sender,
a.SentDate,
a.Summary,
a.Likes,
a.Dislikes,
a.Tags,
a.PostMode,
c.CategoryID,
c.CategoryTitle,
AcceptedCommentsCount =
(from com in context.Module_Articles_Comments where com.ArticleID == a.ArticleID && com.Status select com)
.Count(),
DeniedCommentsCount =
(from com in context.Module_Articles_Comments where com.ArticleID == a.ArticleID
&& com.Status == false select com)
.Count()
}).ToList();

How do I build up a LINQ => SQL / entities query (with joins) step-by-step?

I have the following two LINQ queries:
public int getJobsCount()
{
var numJobs =
(from j in dbConnection.jobs
join i in dbConnection.industries on j.industryId equals i.id
join c in dbConnection.cities on j.cityId equals c.id
join s in dbConnection.states on j.stateId equals s.id
join pt in dbConnection.positionTypes on j.positionTypeId equals pt.id
select j).Count();
return numJobs;
}
public List<Job> getJobs()
{
var jobs =
(
from j in dbConnection.jobs
join i in dbConnection.industries on j.industryId equals i.id
join c in dbConnection.cities on j.cityId equals c.id
join s in dbConnection.states on j.stateId equals s.id
join pt in dbConnection.positionTypes on j.positionTypeId equals pt.id
orderby j.issueDatetime descending
select new Job { x = j.field, y = c.field, etc }
).Skip(startJob - 1).Take(numJobs);
return jobs;
}
There's a lot of duplicate code in there - the "from", and "join" lines are identical, and I'll be adding in some "where" lines as well that will also be identical.
I tried adding a method that returned an IQueryable for the first part:
public IQueryable getJobsQuery()
{
var q =
from j in dbConnection.jobs
join i in dbConnection.industries on j.industryId equals i.id
join c in dbConnection.cities on j.cityId equals c.id
join s in dbConnection.states on j.stateId equals s.id
join pt in dbConnection.positionTypes on j.positionTypeId equals pt.id;
return q;
}
...but I get "a query body must end with a select clause or a group clause".
If I add a select clause on to the end off that function, I can't call count() on the result:
// getJobsQuery:
var q = from j in dbConnection.jobs
join i in dbConnection.industries on j.industryId equals i.id
join c in dbConnection.cities on j.cityId equals c.id
join s in dbConnection.states on j.stateId equals s.id
join pt in dbConnection.positionTypes on j.positionTypeId equals pt.id
select new { a = j.y, b = c.z }
// another method:
var q = getJobsQuery();
var numJobs = q.Count(); // "IQueryable doesn't contain a definition for count"
Is there a way to build up this query step-by-step to avoid duplicating a whole lot of code?

There are two ways of writing LINQ-queries, and though it doesn't really matter witch one you use it's good to know both of them cause they might learn you something about how LINQ works.
For instance, you have a set of jobs. If you were to select all jobs with an industryId of 5 (wild guess of data-types) you'd probably write something like this:
from j in dbConnection.jobs
where j.inustryId == 5
select j;
The very same query can also be written like this
dbConnections.jobs.Where(j => j.industryId == 5);
Now, I'm not here to preach saying one way is better than the other, but here you can clearly see how LINQ using the extension-methods syntax automatically selects on the iterated object (unless you do a select), whereas in the query-syntax you must do this explicitly. Also, if you were to add inn another where clause here it would look something like this:
from j in dbConnection.jobs
where j.inustryId == 5 // not using && here just to prove a point
where j.cityId == 3 // I THINK this is valid syntax, I don't really use the query-syntax in linq
select j;
While in the extension-methods you can just append more method-calls like so:
dbConnections.jobs.Where(j => j.industryId == 5)
.Where(j => j.cityId == 3);
Now this is good to know cause this means you can just put your linq-query inside a function an continue querying it. And all you need to do to make it work in your case is just explicitly select the starting variable j, or all the variables you need like so:
var q =
from j in dbConnection.jobs
join i in dbConnection.industries on j.industryId equals i.id
join c in dbConnection.cities on j.cityId equals c.id
join s in dbConnection.states on j.stateId equals s.id
join pt in dbConnection.positionTypes on j.positionTypeId equals pt.id;
select new {j = j, i = i, c = c, s = s, pt = pt };
return q;
Then you should be able to do for instance this:
getJobsQuery().Where(a => a.i.id == 5); // I used a as a name for "all", like the collection of variables
or using the query-syntax
from a in getJobsQuery()
where a.i.id == 5
select a;

Would this be better solved by returning a set of data (e.g. the common data) and querying for a subset of that data?
E.g. [pseudocode]
var allJobs =
(from j in dbConnection.jobs
join i in dbConnection.industries on j.industryId equals i.id
join c in dbConnection.cities on j.cityId equals c.id
join s in dbConnection.states on j.stateId equals s.id
join pt in dbConnection.positionTypes on j.positionTypeId equals pt.id
select j);
var myJobs = allJobs.OrderBy(j => j.issuedate).skip(expr).Take(allJobs.Count);
or similar...