As you can see I'm executing the query for the first element in the list.
I would like to execute the query for each category in the list and to return one collection with the result of all queries without duplicates (A question can be in multiple categories).
public ObservableCollection<Question> GetQuestionsByCategory(List<Category> categories)
{
var c = categories[0];
var questions = from q in this.Questions where q.Categories.Contains(c)
select q;
return new ObservableCollection<Question>(questions);
}
You could do this:
var questions =
(from c in categories
from q in this.Questions where q.Categories.Contains(c)
select q).Distinct();
But I'd suggest this instead:
var questions = from q in this.Questions
where q.Categories.Any(c => categories.Contains(c))
select q;
Related
I have multiple Link queries loading to a IEnumerable list
var queries = new List<IEnumerable<Customers>>();
queries.Add(from c in context.Customers where c.region = 'NE' select c);
queries.Add(from c in context.Customers where c.region = 'SW' select c);
//want count of customers in those two regions
var result = queries.Sum(q => Count());
However it is returning a count of the queries (2), not count of the Customers.
How can execute the List of IEnumerable queries?
The mistake is at the last line:
q => Count()
Instead of actually counting the elements in a sequence, which would be q => q.Count(), you are calling a method Count() of either a current instance or the current class.
Actually, there is no need to do two separate queries. Instead, use a single query:
var query = from c
in context.Customers
where c.region = 'NE' || c.region = 'SW'
select c;
var result = query.Count();
or, slightly shorter:
var result = context.Customers.Count(c => c.region = 'NE' || c.region = 'SW');
I'm working on this LINQ query. I'd like the resulting list return a list of records that contain duplicates exclusively, based on the EMailAddress1 field and grouped by the EMailAddress1 field.
For instance:
emailaddress1#gmail.com
emailaddress1#gmail.com
emailaddress2#gmail.com
emailaddress2#gmail.com
emailaddress2#gmail.com
emailaddress3#gmail.com
emailaddress3#gmail.com
etc.
Any advice on this? Thanks.
var contacts = (from c in xrm.ContactSet
where c.StateCode != 1
orderby c.EMailAddress1, c.CreatedOn
descending select new {
c.FirstName,
c.LastName,
c.EMailAddress1,
c.ContactId,
c.CreatedOn }).ToList();
Based on your previous query:
var duplicatedEmails = (from c in contacts
group c by c.EMailAddress1 into g
where g.Count() > 1
select g.Key).ToList();
var duplicatedContacts = contacts.Where(c => duplicatedEmails.Contains(c.EMailAddress1));
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();
I got two tables: comments and commentLikes
in the same query i count the likes users have given on a comment.
I got the following (simplified) query:
var res = (from c in db.Comments
where c.Topic.ID == topicID
select new
{
comment = c,
count = c.CommentLikes.Count()
}).ToList();
But, rather than mapping the likecount into the comment entity again, I'd like to get a list of Comments only with a field LikeCount in it, preferably with an efficient query. Something like this:
var res = (from c in db.Comments
where c.Topic.ID == topicID
select new
{
comment = c,
c.LikeCount = c.CommentLikes.Count()
}).ToList();
This query doesn't compile.
How to do this in linq?
You can't do that. EF does not support to project (= select) data into an entity. You must fill the LikeCount property in memory after the query has been executed. You can write it in a compact way, but it's basically just a foreach loop over the materialized anonymous objects:
IEnumerable<Comment> res =
(from c in db.Comments
where c.Topic.ID == topicID
select new
{
comment = c,
count = c.CommentLikes.Count()
})
.ToList() // DB query runs here, the rest in memory
.Select(a => {
a.comment.LikeCount = a.count;
return a.comment;
});
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.