Lets say I have this IQueryable variable :
var result= (from fruit in fruitTable
join dapple in applesIQuery on fruit.fruitType equals dapple.fruitType into apples
from apple in apples.DefaultIfEmpty()
select new foo );
applesIQuery comes from another IQueryable that consists of another group of joins.
applesIQuery =(from a in anotherTable select new {id = foo}) ;
I need to treat the case where applesIQuery == null, basically creating a List of 1 element with id=0 , but without transforming the IQueryable into an IEnumerable. Something like :
applesIQuery =(from a in anotherTable select new {id = foo})?? Iqueriable {new {id=0}} ;
Any pointers towards the right direction ?
applesIQuery is of type IQueryable and will not be null. Assuming you mean that if the query does not return any results, try something like this:
applesIQuery = applesIQuery.Count() == 0 ? new ArrayList(){ new { id = 0 } }.AsQueryable() : applesIQuery;
Related
My code is as below:
var conntionRecord1Id = (from connectionBase in orgServiceContext.CreateQuery("connection")
where connectionBase["record1roleid"] == null
select new { OpportunityId = connectionBase["record1id"] }).Distinct().ToList();
var query =
from opportunity in orgServiceContext.CreateQuery("opportunity")
orderby opportunity["createdon"] ascending
select new
{
Topic = opportunity.Attributes.Contains("name") == true ? opportunity["name"] : null,
OpportunityId = opportunity.Attributes.Contains("opportunityid") == true ? opportunity["opportunityid"] : null,
PostalCode = opportunity.Attributes.Contains("new_address_postalcode") == true ? opportunity["new_address_postalcode"] : null,
};
var result = (from f in query.ToList() where conntionRecord1Id.Contains(f.OpportunityId) select f).ToList();
But in above query where i am using Contains it giving count 0. even though I have common records in the list
The Contains Linq extension method does not know how to compare complex objects.
Comparing f.OpportunityId to a list of Guids instead of a list of an anonymous type will work:
var conntionRecord1Id = (from connectionBase in orgServiceContext
.CreateQuery("connection")
where connectionBase["record1roleid"] == null
select connectionBase.GetAttributeValue<Guid?>("record1id"))
.Distinct()
.ToList();
Implement IEqualityComparer in a custom comparer class to compare complex objects: https://stackoverflow.com/a/6694563/1817350
Keep in mind that calling .ToList() brings down all the records into memory and will cause performance problems with large amounts of records.
I have two tables..
Student (StudentId,Name,FatherName)
Qualification (QualificationId,StudentId,DegreeName)
I have got data like this..
var myList = (from c in entities.Students
join q in entities.Qualifications on c.StudentId equals q.StudentId
select new {c.Name,c.FatherName,q.DegreeName}).ToList();
Now i want to filter myList more.. How can i do it, like..
var filteredList = myList.Select(c=> new Student
{
Name=c.Name,
FatherName=c.FatherName
//Degree=C.Degree
}).ToList();
The above Linq Query is not working if i want to get DegreeName also, My Question is how to further Filter myList.
Thanks.
var filteredList = myList.Where(i => i.FatherName == "Shahid").ToList();
Keep in mind since you called ToList() on the original query you are now filtering in memory. If you want to filter in the database then remove the ToList() on the first query and do it like this:
var myList = from c in entities.Students
join q in entities.Qualifications on c.StudentId equals q.StudentId
select new {
c.Name,
c.FatherName,
q.DegreeName
};
var filteredInDatabase = myList.Where(i => i.FatherName == "Shahid").ToList();
First Table is the View and Second is the result I want
This below query works fine
List<BTWStudents> students = (from V in db.vwStudentCoursesSD
where classIds.Contains(V.Class.Value)
select new BTWStudents
{
StudentId = V.StudentId
Amount= V.PaymentMethod == "Cashier Check" ? V.Amount: "0.00"
}).Distinct().ToList();
But I changed it to List to add string formatting(see below)
List<BTWStudents> students = (from V in db.vwStudentCoursesSD
where classIds.Contains(V.Class.Value)
select new {V}).ToList().Select(x => new BTWStudents
{
StudentId = V.StudentId
Amount= V.PaymentMethod == "Cashier Check" ? String.Format("{0:c}",V.Amount): "0.00"
}).Distinct().ToList();
With this Second Query I get this
Why is distinct not working in the second query?
When working with objects (in your case a wrapped anonymous type because you are using Select new {V} rather than just Select V), Distinct calls the object.Equals when doing the comparison. Internally, this checks the object's hash code. You'll find in this case, the hash code of the two objects is different even though the fields contain the same values. To fix this, you will need to override Equals on the object type or pass a custom IEqualityComparer implementation into the Distinct overload. You should be able to find a number of examples online searching for "Distinct IEqualityComparer".
Try this (moved your distinct to the first query and corrected your bugged if/then/else):
List<BTWStudents> students = (from V in db.vwStudentCoursesSD
where classIds.Contains(V.Class.Value)
select new {V}).Distinct().ToList().Select(x => new BTWStudents
{
classId = V.Class.HasValue ? V.Class.Value : 0,
studentName = V.StudentName,
paymentAmount = V.PaymentMethod == "Cashier Check" ? String.Format("{0:c}",x.V.AmountOwed): "0.00"
}).ToList();
You can get around using Distinct all together if you Group by StudentID
var studentsGroupedByPayment =
(from V in db.vwStudentCoursesSD
where classIds.Contains(V.Class.Value)
group V by V.StudentId into groupedV
select new
{
StudentID = groupedV.Key,
Amount = string.Format("{0:C}",
groupedV.First().PaymentMethod == "Cashier Check" ?
groupedV.First().Amount : 0.0)
}
).ToList();
I am trying to write a linq query that will only return certain columns from my entity object into a list object.
Below is my code which produces an error(can't implicitly convert a generic list of anonymous types to a generic list of type TBLPROMOTION):
IQueryable<TBLPROMOTION> matches = webStoreContext.TBLPROMOTION.Include("TBLSTORE").Include("LKPROMOTIONTYPE");
List<TBLPROMOTION> promotionInfo = null;
promotionInfo = (from p in matches
orderby p.PROMOTION_NM descending
select new { p.EFFECTIVE_DT, p.EXPIRE_DT, p.IS_ACTIVE,
p.PROMOTION_DESC, p.PROMOTION_ID, p.PROMOTION_NM }).ToList();
What would be the best way to accomplish this. I do not want to do a "select p" in this case and return all the columns associated with the query.
thanks in advance,
Billy
Can't you do var promotionInfo = () and get a list of anonymous types?
Okay, basically you can not cast an Anonymous type to a known type like TBLPROMOTION.
ofcourse, you can say var promotionInfo = and then get an IEnumerable<{Anonymoustype}> and use that to do, what you were wanting to do with promotionInfo.
Also, personally I prefer the Fluent version of a linq query, easy on the eyes, good programming diet, at least for me :)
var promotionInfo = matches
.OrderByDescending( p => p.PROMOTION_NM)
.Select( p => new { p.EFFECTIVE_DT,
p.EXPIRE_DT,
p.IS_ACTIVE,
p.PROMOTION_DESC,
p.PROMOTION_ID,
p.PROMOTION_NM})
.ToList();
If you're moving from a L2E query to a Type already defined, you may need a step between. I haven't tried to compile this but something like:
List<TBLPROMOTION> promotions = new List<TBLPROMOTION>();
var results = from p in matches
orderby p.PROMOTION_NM descending
select new
{
p.EFFECTIVE_DT,
p.EXPIRE_DT,
p.IS_ACTIVE,
p.PROMOTION_DESC,
p.PROMOTION_ID,
p.PROMOTION_NM
};
foreach (var v in results)
{
promotions.Add(new TBLPROMOTION(v.EFFECTIVE_DT, v.EXPIRE_DT, v.IS_ACTIVE,
v.PROMOTION_DESC, v.PROMOTION_ID, v.PROMOTION_NM));
}
Based on the comment below, you might try something like:
foreach(var v in results)
{
TBLPROMOTION temp = new TBLPROMOTION();
temp.EFFECTIVE_DT = v.EFFECTIVE_DT;
temp.EXPIRE_DT = v.EXPIRE_DT;
temp.IS_ACTIVE = v.IS_ACTIVE
// Assign Other Properties
promotions.Add(temp);
}
.......
Sorry: Just read the addition to the top.
Are you sure that none of the fields you're leaving out (instead of saying "select p") are required for a TBLPROMOTION object? Also, sense your TBLPROMOTION object is going to have properties (and therefore memory allocated) for those skipped fields, why not just use an annonymous type or set up a helper class that contains only your needed properties?
#Billy, following code worked for me.
List<TBLPROMOTION> promotionInfo =
(from p in matches
orderby p.PROMOTION_NM descending
select new TBLPROMOTION(p.EFFECTIVE_DT, p.EXPIRE_DT, p.IS_ACTIVE,
p.PROMOTION_DESC, p.PROMOTION_ID, p.PROMOTION_NM)
).ToList();
did you try
select new TBLPROMOTION {.....
instead of
select new {.....
List<TBLPROMOTION> promotionInfo = null;
promotionInfo = (from p in matches
orderby p.PROMOTION_NM descending
select new TBLPROMOTION { COL1 = p.EFFECTIVE_DT, COL2 = p.EXPIRE_DT, COL3 = p.IS_ACTIVE... }).ToList();
Where COL1, COL2, ... are the names of the properties on TBLPROMOTION you wish you populate.
If you want a subset of the table you have 2 options:
#Fredou mentioned select new TBLPROMOTION{...}
other way is to create a custom DTO which has the exact properties & select them instead like:
List promotionInfo = ...
select new TBLPROMOTION_DTO{
Effective_dt = ...
}
HTH
I have this fragment of code:
SmsDataClassesDataContext dc = new SmsDataClassesDataContext();
// Get the customer
Customer currentCustomer = dc.Customers.Single( c => c.Hash1 == forThisHash );
// Get from Name (LINQ to XML)
var q = from c in thisSmsPack.Descendants("from")
select c;
string from = q.First().Value;
foreach ( XElement element in thisSmsPack.Descendants("to") )
{
// Create the queue
SmsQueue sq = new SmsQueue();
sq.CustomerId = currentCustomer.CustomerId;
sq.MsgFrom = from;
sq.MsgTo = element.Attribute("name").Value;
sq.MsgPhone = element.Attribute("phone").Value;
sq.MsgBody = element.Attribute("msg").Value;
sq.Priority = currentCustomer.SendsSmsAtPriority;
sq.DontSendUntil = GetNextSendDate();
// sq.TimeCreated = System.DateTime.Now;
currentCustomer.SmsQueues.Add(sq);
}
dc.SubmitChanges();
I am creating new instances of "SmsQueues", populating the values and when the foreach loop is finished I submit the changes. Given the new lambda/linq/anonymous types that .NET 3.5 has, is there a more "modern" way to accomplish the above?
As a side question, maybe related, can I return an existing type composed of different columns in the select part of the linq expression?
Suppose you have three tables:
T1 == T1.Id, T1.Name
T2 == T2.Id, T2.Phone
T3 == T3.Name, T3.Phone, T3.SomethingElse
Can I perform a LINQ query that returns:
T1.Name, T2.Phone, SomethingElseNew
And let .NET know that that is of Type T3 (and it's a new instance of it)?
That way when I SubmitChanges, new T3 instances are inserted in the DB?
I don't know if I make myself clear :S
I don't have a system available to test this, but I think this (or something very close) should work.
CustomerId = currentCustomer.CustomerId;
var sqrange = from element in thisSmsPack.Descendants("to") )
select new SmsQueue
{
// Create the queue
MsgFrom = from,
MsgTo = element.Attribute("name").Value,
MsgPhone = element.Attribute("phone").Value,
MsgBody = element.Attribute("msg").Value,
Priority = currentCustomer.SendsSmsAtPriority,
DontSendUntil = GetNextSendDate()
// TimeCreated = System.DateTime.Now
};
currentCustomer.SmsQueues.AddRange(sqrange);
EDIT: Fixed the numerous syntax errors (as delineated in the comments)
You could do something like this (syntax may be off slightly, no intellisense here):
var q = T1.Join(T2, t => t.Id, t2 => t2.Id)
select new T3{Name=t.Name,Phone=t2.Phone,SomethingElseNew="Chickens"};