Develop Reference

Linq variable inside select

I have a following query
return _context.Table1
.Where(x => x.ContactId == contactKey.Id)
.Include(x => x.Table2)
.Include(x => x.Table3.Table4)
.Select(a =>
new MyReadModel
{
PriorityAssignment = true,
LastContactedDate = (a.Table3.Table4 != null && a.Table3.Table4.FirstOrDefault(h =>
h.Id == a.Table2.FkId
) != null ?
a.Table3.Table4.FirstOrDefault(h => && h.Id == a.Table2.FkId
).LastContactedDatetime : default
)
}
)
.ToListAsync();
What i wants is to simplify LastContactedDate assignment with in select. I think we can assign
a.Table3.Table4.FirstOrDefault(h =>
h.Id == a.Table2.FkId
)
to some variable but can't able to do it
can someone identify what is needed

With EF Core you don't have to check for null, LINQ Translator do not execute your code, but uses it for translation to the SQL. Also Includes is not needed if you do not retrieve whole objects.
return await _context.Table1
.Where(x => x.ContactId == contactKey.Id)
.Select(a => new MyReadModel
{
PriorityAssignment = true,
LastContactedDate = (DateTime?)a.Table3.Table4.Where(h => h.Id == a.Table2.FkId)
.OrderByDescending(h => LastContactedDatetime)
.Select(h => LastContactedDatetime)
.FirstOrDefault()
}).ToListAsync();

you can use it like this example
List<string> someList= new List<string>();
someList= someList.Select(x =>
{
var newVariable= "newVariable";
return newVariable;
}).ToList();
in your case
return _context.Table1
.Where(x => x.ContactId == contactKey.Id)
.Include(x => x.Table2)
.Include(x => x.Table3.Table4)
.Select(a => {
Table4 newVariable = null;
if(a.Table3.Table4 != null)
newVariable = a.Table3.Table4.FirstOrDefault(h => h.Id == a.Table2.FkId;
var result = new MyReadModel
{
PriorityAssignment = true,
LastContactedDate = (newVariable != null ? newVariable.LastContactedDatetime : default
)
};
}
) .ToListAsync();

convert SQL with subquery to LINQ (lamda expression)

Need help with converting this sql query
SELECT c.studentId, c.Name
FROM Classes c
WHERE c.Class = 'Math'
AND c.Grade IN 'yoklama', '2')
AND c.studentId IN (
SELECT c2.studentId
FROM Classes c2
WHERE c2.Class = 'Eng'
AND c.Grade IN ('yoklama', '2'))
I was trying like this but these keeps giving error that I am doing this wrong
var reportDtos = context.Classes.Where(c => pt.Class == 'Math' && c.Grade.HasValue
&& c.Grade == '2' || c.Grade == 'yoklama' && c.studentId.Contains(context.ParticipTests
.Where(x => x.Class == 'Math' &&x.Grade.HasValue && x.Grade == '2' || x.Grade == 'yoklama')
.ToList()
.Select(x => ))
.Include("Area")
.Include("Questions")
.Include("Class.Test")
.ToList()
.Select(pt => new ReportDto
{
...
}

First off, strings must always be double quoted " and not single quoted ' like you have some.
If you write some code by splitting up the steps it makes it more understandable.
var validGrades = new List<string> { "Yoklama", "2" };
var studentsInEnglish = context.ParticipTests
.Where(x => x.Class.Equals("Eng") && validGrades.Contains(x.Grade))
.Select(x => x.studentId);
var studentsInMath = context.Classes
.Where(x => x.Class.Equals("Math") && validGrades.Contains(x.Grade) && studentsInEnglish.Contains(x.studentId))
.Select(x => (x.studentId, x.Name));
Now with this, (if you really still want to) you can write a single query by plugging in and replacing.
var reportDtos = context.ParticipTests
.Where(
x => x.Class.Equals("Math") &&
new List<string> { "Yoklama", "2" }.Contains(x.Grade) &&
context.Classes
.Where(
y => y.Class.Equals("Eng") &&
new List<string> { "Yoklama", "2" }.Contains(y.Grade))
.Select(y => y.studentId)
.Contains(x.studentId))
.Select(x => (x.studentId, x.Name))
.ToList();
...But I like the first way better.

C# Linq Lambda for group by multiple columns select max

I want to translate this into lambda syntax and can't seem to get it to work:
Grouping by two columns, select max on a different column, return list of complete complex object.
I am writing more text here to get past the validation on this form. How much text is needed until I am allowed to post this?
_clientpolicies = (from policy in
_reply.CommercialInsuredGroupWithPolicyTerm.InsuredWithPolicyTerm.SelectMany(x => x.PolicyTerm)
.Where(x => !(string.IsNullOrWhiteSpace(x.PolicyNumber) && string.IsNullOrWhiteSpace(x.ControlNumber)))
.Where(x => x.Insured.DNBAccountNumber == _client.LookupID)
group policy by
new
{
PolicyReference = GetPolicyReference(policy),
PolicyType = policy.ProductInformation.PolicyTypeCode
}
into g
let maxPolicyInception = g.Max(p => p.InceptionDate)
from policyGroup in g
where policyGroup.InceptionDate == maxPolicyInception
select policyGroup).ToList();

I dont think there's a way of doing it in one line. So there's my try :
policyGroups=
_reply.CommercialInsuredGroupWithPolicyTerm.InsuredWithPolicyTerm
.SelectMany(x => x.PolicyTerm)
.Where(x => !(string.IsNullOrWhiteSpace(x.PolicyNumber) && string.IsNullOrWhiteSpace(x.ControlNumber)))
.Where(x => x.Insured.DNBAccountNumber == _client.LookupID)
.GroupBy(x => GetPolicyReference(x))
.ThenBy(x => x.ProductInformation.PolicyTypeCode)
.ToList();
var maxPolicyInception = policyGroups.Max(p => p.InceptionDate);
_clientpolicies = policyGroups
.Where(g => g.InceptionDate == maxPolicyInception)
.ToList();

_clientpolicies =
_reply.CommercialInsuredGroupWithPolicyTerm.InsuredWithPolicyTerm.SelectMany(x => x.PolicyTerm)
.Where(x => !(string.IsNullOrWhiteSpace(x.PolicyNumber) && string.IsNullOrWhiteSpace(x.ControlNumber)))
.Where(x => x.Insured.DNBAccountNumber == _client.LookupID)
.GroupBy(x =>
new
{
PolicyReference = GetPolicyReference(x),
PolicyType = x.ProductInformation.PolicyTypeCode
},
(key, g) => g.OrderByDescending(gx => gx.InceptionDate).First()

Use same, looked-up value across multiple linq Where clauses without looking up more than once

I have a LINQ query which has three Where clauses. In each Where clause I am looking up the same set of items in order to compare values:
var items = _umbracoHelper.GetPage(ItemsPage.ModelTypeAlias).Children
.Where(x => level1Category == 0 || x
.GetPropertyValue<IEnumerable<IPublishedContent>>(UmbracoAlias.Item.Categories)
.Select(y => y.Id).Contains(level1Category))
.Where(x => !level2Categories.Any() || x
.GetPropertyValue<IEnumerable<IPublishedContent>>(UmbracoAlias.Item.Categories)
.Select(y => y.Id).Intersect(level2Categories.AsEnumerable()).Any())
.Where(x => !level3Categories.Any() || x
.GetPropertyValue<IEnumerable<IPublishedContent>>(UmbracoAlias.Item.Categories)
.Select(y => y.Id).Intersect(level3Categories.AsEnumerable()).Any());
Is there a way I can get the value of UmbracoAlias.Items.Categories once and store that value to be used in the other where clauses without causing the GetPropertyValue method to execute more than once?

You can pair up each item with category IDs, like this:
var items = _umbracoHelper.GetPage(ItemsPage.ModelTypeAlias).Children
.Select(c => new {
Child = c
, CategoryIds = c
.GetPropertyValue<IEnumerable<IPublishedContent>>(UmbracoAlias.Item.Categories)
.Select(y => y.Id)
.ToList()
})
.Where(x => level1Category == 0 || x.CategoryIds.Contains(level1Category))
.Where(x => !level2Categories.Any() || x.CategoryIds.Intersect(level2Categories.AsEnumerable()).Any())
.Where(x => !level3Categories.Any() || x.CategoryIds.Intersect(level3Categories.AsEnumerable()).Any())
.Select(x => x.Child);
This does the filtering on children paired up with their category IDs, and then keeps only the Child object in the final projection.
You could further simplify this by combining all three Where clauses:
var items = _umbracoHelper.GetPage(ItemsPage.ModelTypeAlias).Children
.Where(c => {
var categoryIds = c
.GetPropertyValue<IEnumerable<IPublishedContent>>(UmbracoAlias.Item.Categories)
.Select(y => y.Id)
.ToList();
if (level1Category != 0 && !categoryIds.Contains(level1Category)) {
return false;
}
if (level2Categories.Any() && !categoryIds.Intersect(level2Categories.AsEnumerable()).Any()) {
return false;
}
if (level3Categories.Any() && !categoryIds.Intersect(level3Categories.AsEnumerable()).Any()) {
return false;
}
return true;
});

MVC4 Linq Query Optimisation

I have the below code which works but I do not feel this is the best way to achieve the result. I am looking at optimising my code. Any suggestions of a better option will be appreciated. sub is a subcategory which is nullable.
[AllowAnonymous]
public ActionResult _relatedgrps(string cat, string sub)
{
if (!string.IsNullOrWhiteSpace(sub)){
var pgs = db.Pages
.Where(u=>u.MetaNoSearch==false)
.Where(u => u.PaOk == true && u.Category.Name == cat && u.SubCategory.CatName == sub)
.OrderByDescending(u => u.PaCreatedOn);
return PartialView(pgs.ToList());
}else{
var pgs = db.Pages
.Where(u=>u.MetaNoSearch==false)
.Where(u => u.PaOk == true && u.Category.Name == cat )
.OrderByDescending(u => u.PaCreatedOn);
return PartialView(pgs.ToList());
}}

Linq IEnumerables can be additive and the query will only be executed when enumerated for the first time (like calling .ToList()). So you should be able to do something like this:
var pgs = db.Pages
.Where(u => u.MetaNoSearch == false &&
u.PaOk == true &&
u.Category.Name == cat);
if (!string.IsNullOrWhiteSpace(sub))
{
pgs = pgs.Where(u => u.SubCategory.CatName == sub);
}
return PartialView(pgs.OrderByDescending(u => u.PaCreatedOn).ToList());

Create an object to query it. To improve it, you also could remove it boolean comparations because they are conditions.
var query = db.Pages.Where(u => !u.MetaNoSearch && u.PaOk && u.Category.Name == cat);
if (!string.IsNullOrWhiteSpace(sub))
query = query.Where(u => u.SubCategory.CatName == sub);
query = query.OrderByDescending(u => u.PaCreatedOn);
return PartialView(query.ToList());

#user3021830 - be careful with String.IsNullOrWhitespace, you cannot use that in a database query. You could do String.IsNullOrWhitespace(sub), but not String.IsNullOrWhitespace(u.*).
I'd avoid any conditionals in the query because that will likely result in a case statement in the SQL.
To produce the best SQL I'd do something like this:
var pgs = db.Pages.Where(u => u.MetaNoSearch == false)
.Where(u => u.PaOk == true)
.Where(u => u.Category.Name == cat);
if (!string.IsNullOrWhiteSpace(sub))
{
pgs = pgs.Where(u => u.SubCategory.CatName == sub);
}
var result = pgs.OrderByDescending(u => u.PaCreatedOn).ToList();