I have a List of objects that I need sorted a particular way.
The relevant table fields are:
ID (int)
IsMandatory (bit)
ParentID (int nullable)
Code (varchar)
I need them sorted by IsMandatory=true first, then by Code, but anything with a ParentID must be sorted by Code but appear straight after the row with the same ID as ParentID (and these records will always have IsMandatory set to NULL).
Some sample data, and this is also in the order in which they should appear when ordered:
ID=1, IsMandatory=1, ParentID=NULL, Code="A"
ID=2, IsMandatory=NULL, ParentID=1, Code="A"
ID=3, IsMandatory=NULL, ParentID=1, Code="B"
ID=4, IsMandatory=1, ParentID=NULL, Code="B"
ID=5, IsMandatory=0, ParentID=NULL, Code="C"
ID=6, IsMandatory=NULL, ParentID=5, Code="A"
ID=7, IsMandatory=0, ParentID=NULL, Code="D"
How would this best be accomplished in a Linq to SQL orderby?
It was a difficult sort!
The reason for the difficulty stems from the fact you are ordering on the Parents record properties first and then the actual records properties.
I tried to make the variables as self explanatory as possible, but if you have any questions please ask!
var query = from x in context.Table
let parent = list.FirstOrDefault(y => x.ParentID == y.ID)
let parentIsMandatory = parent == null ? x.IsMandatory : parent.IsMandatory
let parentIsMandatoryOrder = parentIsMandatory == true ? 0 : 1
let parentCode = parent == null ? x.Code : parent.Code
let parentId = x.ParentID ?? x.ID
let isParent = x.ParentID == null ? 0 : 1
orderby parentIsMandatoryOrder, parentCode, parentId, isParent, x.Code
select x;
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.
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();
So I wanted to make a linq query out of my left join sql (refer to it below). I just don't know how to properly position the ".TournamentId = 1" condition on the joins. Currently when running this on my database I get the results that I want. which is a couple of rows from the Type table with null fields.
select typ.Id, stat.PromoterId, temp.PromoterId
from ReportTypes type
left join ReportTemplateStatus status on status.PromoterId = type.TypeId and status.TournamentId = 1
left join ReportTemplates temp on temp.ClientId = status.PromoterId and temp.TournamentId = 1
Promoter
- promoterId
- promoterName
Tournament
- tournamentId
- tournamentName
ReportType
- TypeId
ReportTemplateStatus
- promoterId (this is the key)
- tournamentId
- typeId
ReportTemplates
- promoterId
- tournamentId
This is currently what I have:
var report = from type in context.ReportTypes
join status in context.ReportTemplateStatus on type.TypeId equals status.TypeId
join temp in context.ReportTemplates on status.promoterId equals temp.promoterId into iReports
from reports in iReports.Where (rep => rep.promoterId == _promoterId && rep.tournamentId == _tournamentId).DefaultIfEmpty()
select new { my fields});
but it's giving me a null.
any ideas on how the linq should work? maybe separate into "itables" (iReports) or something?
This should give you what you are looking for
var report = from type in context.ReportTypes
from status in context.ReportTemplateStatus.Where(x => type.TypeId == x.TypeId)
.Where(x => x.TournamentId == 1)
.DefaultIfEmpty()
from reports in context.ReportTemplates.Where(x => status.promoterId == x.promoterId)
.Where(x => x.TournamentId == 1)
.DefaultIfEmpty()
select new { my fields};
You can use like this
var query = from person in people
join pet in pets on person equals pet.Owner into gj
from subpet in gj.DefaultIfEmpty()
select new { person.FirstName, PetName = (subpet == null ? String.Empty : subpet.Name) };
Thanks
I am looking to optimize my LINQ query because although it works right, the SQL it generates is convoluted and inefficient...
Basically, I am looking to select customers (as CustomerDisplay objects) who ordered the required product (reqdProdId), and are registered with a credit card number (stored as a row in RegisteredCustomer table with a foreign key CustId)
var q = from cust in db.Customers
join regCust in db.RegisteredCustomers on cust.ID equals regCust.CustId
where cust.CustomerProducts.Any(co => co.ProductID == reqdProdId)
where regCust.CreditCardNumber != null && regCust.Authorized == true
select new CustomerDisplay
{
Id = cust.Id,
Name = cust.Person.DisplayName,
RegNumber = cust.RegNumber
};
As an overview, a Customer has a corresponding Person which has the Name; PersonID is a foreign key in Customer table.
If I look at the SQL generated, I see all columns being selected from the Person table. Fyi, DisplayName is an extension method which uses Customer.FirstName and LastName. Any ideas how I can limit the columns from Person?
Secondly, I want to get rid of the Any clause (and use a sub-query) to select all other CustomerIds who have the required ProductID, because it (understandably) generates an Exists clause.
As you may know, LINQ has a known issue with junction tables, so I cannot just do a cust.CustomerProducts.Products.
How can I select all Customers in the junction table with the required ProductID?
Any help/advice is appreciated.
The first step is to start your query from CustomerProducts (as Alex Said):
IQueryable<CustomerDisplay> myCustDisplay =
from custProd in db.CustomerProducts
join regCust in db.RegisteredCustomers
on custProd.Customer.ID equals regCust.CustId
where
custProd.ProductID == reqProdId
&& regCust.CreditCardNumber != null
&& regCust.Authorized == true
select new CustomerDisplay
{
Id = cust.Id,
Name = cust.Person.Name,
RegNumber = cust.RegNumber
};
This will simplify your syntax and hopefully result in a better execution plan.
Next, you should consider creating a foreign key relationship between Customers and RegisteredCustomers. This would result in a query that looked like this:
IQueryable<CustomerDisplay> myCustDisplay =
from custProd in db.CustomerProducts
where
custProd.ProductID == reqProdId
&& custProd.Customer.RegisteredCustomer.CreditCardNumber != null
&& custProd.Customer.RegisteredCustomer.Authorized == true
select new CustomerDisplay
{
Id = cust.Id,
Name = cust.Person.Name,
RegNumber = cust.RegNumber
};
Finally, for optimum speed, have LINQ compile your query at compile time, rather than run time by using a compiled query:
Func<MyDataContext, SearchParameters, IQueryable<CustomerDisplay>>
GetCustWithProd =
System.Data.Linq.CompiledQuery.Compile(
(MyDataContext db, SearchParameters myParams) =>
from custProd in db.CustomerProducts
where
custProd.ProductID == myParams.reqProdId
&& custProd.Customer.RegisteredCustomer.CreditCardNumber != null
&& custProd.Customer.RegisteredCustomer.Authorized == true
select new CustomerDisplay
{
Id = cust.Id,
Name = cust.Person.Name,
RegNumber = cust.RegNumber
};
);
You can call the compiled query like this:
IQueryable<CustomerDisplay> myCustDisplay = GetCustWithProd(db, myParams);
I'd suggest starting your query from the product in question, e.g. something like:
from cp in db.CustomerProducts
join .....
where cp.ProductID == reqdProdID
As you have found, using a property defined as an extension function or in a partial class will require that the entire object is hydrated first and then the select projection is done on the client side because the server has no knowledge of these additional properties. Be glad that your code ran at all. If you were to use the non-mapped value elsewhere in your query (other than in the projection), you would likely see a run-time exception. You can see this if you try to use the Customer.Person.DisplayName property in a Where clause. As you have found, the fix is to do the string concatenation in the projection clause directly.
Lame Duck, I think there is a bug in your code as the cust variable used in your select clause isn't declared elsewhere as a source local variable (in the from clauses).
I have an odd linq subquery issue.
Given the following data structure:
Parents Children
------- --------
Id Id
ParentId
Location
HasFoo
(obviously this is not the real structure, but it's close enough for this example)
I'm able to run this query and get a desired result:
bool b = (from p in Parents
from c in Children
where p.Id == 1 && c.ParentId == p.Id && c.Location == "Home"
select c.HasFoo).SingleOrDefault();
So if there is a child that has the Location "Home" for a Parent of Id 1, I will get that Child's "HasFoo" value, otherwise, I'll get false, which is the "default" value for a bool.
However, if I try and write the query so I have a list of Parent objects, like so:
var parentList = from p in Parents
select new ParentObject
{
ParentId = p.ParentId,
HasHomeChildren = p.Children.Count(c => c.Location == "Home") > 0,
HasHomeChildrenWithFoo = (from c in p.Children where c.Location == "Home" select c.HasFoo).SingleOrDefault()
}
I get the following error when iterating over the list:
The null value cannot be assigned to a member with type System.Boolean which is a non-nullable value type.
I don't see where this "null" value is coming from, however.
I wonder if the compiler is inferring HasHomeChildrenWithFoo to be bool, but then actually casting to a nullable bool (thus messing up your SingleOrDefault call). At any rate, I'd be willing to bet you could fix it with a cast to a nullable type in that final select which you can then manually default to false when null. It'd probably make the error go away, but it's kind of a brute-force kludge.
var parentList = from p in Parents
select new ParentObject
{
ParentId = p.ParentId,
HasHomeChildren = p.Children.Any(c => c.Location == "Home"),
HasHomeChildrenWithFoo = (from c in p.Children where c.Location == "Home" select (bool?)c.HasFoo) ?? false)
}