I have a linq query like this :
var trfplanList = (from at in entities.tdp_ProviderAccomodationType
join ap in entities.tdp_ProviderAccomodationTariffPlan on at.PATID equals ap.FK_PATID
join ac in entities.tdp_ProviderAccomodationCategory on ap.FK_PACID equals ac.PACID
where at.FK_ProviderID == CityID && at.IsApproved == 0 && ap.IsApproved == 0 && ac.AccomodationCategory == "Double Occupy"
orderby at.AccomodationType,ap.FromDate,ap.SType
select new AccomodationTariff
{
AccomodationType = at.AccomodationType,
SType = ap.SType,
FromDate = Convert.ToDateTime(ap.FromDate),
ToDate = Convert.ToDateTime(ap.ToDate),
RoomTariff = Convert.ToDecimal(ap.Rate),
ExPAXRate = Convert.ToDecimal(at.PerPaxRate)
}).ToList();
I have two questions:
Can't I convert value while assigning in the select new {} block ? it is giving me an error in project.
I want use 'case' while selecting ExPAXRate from the database for example in SQL I used to write :
CASE ap.SType WHEN 'Off Season' THEN at.PerPaxRateOS ELSE at.PerPaxRate END AS ExPAXRate
Can I use something like this in linq query ?
Can't I convert value while assigning in the select new {} block
No, you can't (sadly). EF doesn't know how to translate it into SQL.
I want use 'case'
You can use the ternary operator (?):
ExPAXRate = at.OffSeason ? at.PerPaxRateOS : at.PerPaxRate
(assuming that at.OffSeason exists).
A solution for the conversion issue could be to project into an anonymous type first and then, in memory, to AccomodationTariff:
...
select new
{
AccomodationType = at.AccomodationType,
SType = ap.SType,
FromDate = ap.FromDate,
ToDate = ap.ToDate,
RoomTariff = ap.Rate,
ExPAXRate = at.PerPaxRate
}).AsEnumerable()
.Select(x => new AccomodationTariff
{
AccomodationType = x.AccomodationType,
SType = x.SType,
FromDate = Convert.ToDateTime(x.FromDate),
ToDate = Convert.ToDateTime(x.ToDate),
RoomTariff = Convert.ToDecimal(x.Rate),
ExPAXRate = Convert.ToDecimal(x.PerPaxRate)
}).ToList();
Related
I wrote a query and worked on LINQPAD
from x in FacilityData
from y in FavInformation
where y.UserID == 1 && x.ID == y.FacilityID
select new
{
xID = x.ID,
xDistrictName = (from y in _Ilcelers
where y.ID == x.DistrictID
select y.IlceAd).FirstOrDefault(),
xName = x.Name,
Value = (from o in Tags
from p in Table_tags
where o.Prefix != null && o.Prefix == p._NAME && o.Facility == y.FacilityID
orderby p.İd descending
select new
{
FType = o.TagType,
Name = o.TagsName,
Value = p._VALUE,
Time = p._TIMESTAMP
}).Take(Tags.Count(h => h.Facility == y.FacilityID))
}
result
the result is perfect
but does not work in visual studio,
Value = (from o in DB.Tags
from p in DB.table_tags
where o.Prefix != null && o.Prefix == p.C_NAME && o.Facility == 11
orderby p.id descending
select new
{
FType=o.TagType,
Name = o.TagsName,
Value = p.C_VALUE,
Time = p.C_TIMESTAMP
}).Take(Tags.Count(h => h.Facility == y.FacilityID))
and it gives an error.
I guess the part with .Take() doesn't work because it's linq to EF.
error:
Limit must be a DbConstantExpression or a Db Parameter Reference Expression. Parametre name: count]
error image
thank you have a good day
Not sure but I will just throw it in. If you are talking about linq to ef/sql, it is possible they dont know a thing about C#. If take() would be the problem try to get the select result local first by doing .tolist(). Afterwards use your take funtion.
.ToList().Take(Tags.Count(h => h.Facility == y.FacilityID))
my linq query returns duplicate records like below, how i have to use distinct keyword in this linq query.
var draft_recieved = from df in _DataContext.tblDrafts
from dfBody in _DataContext.DraftBodies
from sendUser in _DataContext.tblSends
where (df.DraftId == dfBody.DraftID) && (df.DraftId == sendUser.DraftId) &&
(sendUser.ToEmailId == (Guid)Membership.GetUser().ProviderUserKey)
select new
{
subject = dfBody.Subject,
draftid = df.DraftId
};
.Distinct() has to be applied as an extension method.
var draft_recieved = (from df in _DataContext.tblDrafts
from dfBody in _DataContext.DraftBodies
from sendUser in _DataContext.tblSends
where (df.DraftId == dfBody.DraftID) && (df.DraftId == sendUser.DraftId) &&
(sendUser.ToEmailId == (Guid)Membership.GetUser().ProviderUserKey)
select new
{
subject = dfBody.Subject,
draftid = df.DraftId
}).Distinct();
I have an array filled with long type values and for each value in the array I need to implement a query. I used foreach loop as you can see from the code below:
var result;
foreach(long id in PrdIdArr)
{
var mainQuery = (from o in db.OPERATIONs
join u in db.UNITs on o.OP_UNIT_ID equals u.UNIT_ID into smt
from s in smt
join x in db.XIDs on s.UNIT_ID equals x.UNIT_ID
where o.OP_OT_CODE == OtCode
where x.IDTYP_CD == "BSN"
where s.START_PRD_ID == id
where o.OP_UPD_DATE >= _StartDate
where o.OP_UPD_DATE <= _EndDate
select new
{
o.OP_ID,
o.OP_UPD_DATE,
x.EXTERNAL_ID,
o.OP_OS_CODE,
o.OP_START,
o.OP_ST_STATION,
s.START_PRD_ID
}).Take(_RowNumber);
//var result = mainQuery.ToList();
result.add(mainQuery.ToList());
}
data = this.Json(result);
data.JsonRequestBehavior = JsonRequestBehavior.AllowGet;
return data;
However, I have a problem in my code; I have to define a main list just before the foreach loop so that I could add results of each query to the that main list. my question is: How can I define this list as you can see at the beginning of my code? Thanks for the help...
How can I define this list as you can see at the beginning of my code?
Make
new {
o.OP_ID,
o.OP_UPD_DATE,
x.EXTERNAL_ID,
o.OP_OS_CODE,
o.OP_START,
o.OP_ST_STATION,
s.START_PRD_ID
}
into a concrete type (say QueryResult, although something a little more specific than that), and then just declare
var result = new List<QueryResult>();
Also, you should consider turning
foreach(long id in PrdIdArr)
and
where s.START_PRD_ID == id
into
where PrdIdArr.Contains(s.Start_PRD_ID)
var result = new List<object>();
foreach(long id in PrdIdArr)
{
....
result.Add(mainQuery.ToList());
}
You could do this:
var result = PrdIdArr.Select(id =>
from o in db.OPERATIONs
join u in db.UNITs on o.OP_UNIT_ID equals u.UNIT_ID into smt
from s in smt
join x in db.XIDs on s.UNIT_ID equals x.UNIT_ID
where o.OP_OT_CODE == OtCode
where x.IDTYP_CD == "BSN"
where s.START_PRD_ID == id
where o.OP_UPD_DATE >= _StartDate
where o.OP_UPD_DATE <= _EndDate
select new
{
o.OP_ID,
o.OP_UPD_DATE,
x.EXTERNAL_ID,
o.OP_OS_CODE,
o.OP_START,
o.OP_ST_STATION,
s.START_PRD_ID
}
.Take(_RowNumber)
.ToList()
).ToList();
I highly recommend performing some Extract Method refactorings, as the code is pretty complex and hard to understand/mange this way.
Just create the anonymous type outside with the same property names and the correct type
var result = Enumerable.Range(0, 0).Select(x => new
{
OP_ID = 1,
OP_UPD_DATE = DateTime.Now,
EXTERNAL_ID = 1,
OP_OS_CODE = 1,
OP_START = DateTIme.Now,
OP_ST_STATION = "",
START_PRD_ID = 1,
}).ToList();
And in your loop call AddRange
result.AddRange(mainQuery.ToList());
Assuming that we have the following table:
Person:
PersonID,
Name,
Age,
Gender
And we are providing a search function that allows users to search the table according to the name and/or the age.
The tricky part in writing the SQL ( or LINQ) query is that the users can choose to search for both field, or any one field, or no field. If he wants to search for all then he would just have to leave the textbox blank.
The logic to do this can be written as follows:
var p;
if(Name_TextBox=='')
{
p=from row in person
select row ;
}
else
{
p= from row in person
where row.Name=Name_TextBox
select row ;
}
// repeat the same for age
Now after a while the code gets very long and messy... How can I compress the above into a single query with no if-else?
Try code like this
string personName = txtPersonName.Text;
int personAge = Convert.ToInt32(txtAge.Text);
var opportunites = from p in this.DataContext.Persons
select new
{
p.PersonID,
p.Name,
p.Age,
p.Gender
};
if (personsID != 0)
opportunites = opportunites.Where(p => p.PersonID == personID);
if (personName != string.Empty)
opportunites = opportunites.Where(p => p.Name.StartsWith(personName));
if (personAge != 0)
opportunites = opportunites.Where(p => p.Age == personAge);
This will work fine. If personName is not given it will be not add to where, and if given then it will added.
One alternative which I have used in SQL which could be implemented in Linq too is
var p = from p in Person
where p.Name == Name_TextBox || Name_TextBox == String.Empty
select p;
(Note that your 'linq' is using SQL syntax, which won't compile. Also you can't declare a var as you are doing without directly assigning a value)
why not use the null coalescing operator? eg.
var products = from a in context.products
where a.ID == (productID ?? a.ID)
select a;
This works really well on my system
What do I put in my order by?? I want to order by Name. I have moved the orderby after the distinct because I read that it needs to be done last.
var result = (from r in db.RecordDocs
where r.RecordID == recordID
select new
{
DocTypeID = r.Document.DocType.DocTypeID,
Name = r.Document.DocType.Name,
Number = r.Document.DocType.Number
}
).Distinct().OrderBy( );
Just do
.OrderBy(doc => doc.Name)
Another option, if you really prefer the query expression syntax would be to chain your query construction across multiple statements:
var query = from r in db.RecordDocs
where r.RecordID == recordID
select new
{
DocTypeID = r.Document.DocType.DocTypeID,
Name = r.Document.DocType.Name,
Number = r.Document.DocType.Number
};
query = query.Disctinct();
query = from doc in query orderby doc.Name select doc;
Since all of these methods are deferred, this will result in the exact same execution performance.