Develop Reference

Using LINQ to get all results where ID in dictionary

i have something like this now, which only searches for 1 LabID
List<Expense> lstExpenses = (from l in ctx.Expenses
where l.datLab.Lab_ID == labID
select l).ToList<Expense>();
how do i return all results where Lab_ID is in a dictionary i have:
the followin functions returns a dictionary value: report.GetLabChildren(labID, "All"); is in <short>,<string> format. i only want to search on the <short>

If you want to do the filtering in linq to objects:
var query = ctx.Expenses.AsEnumerable()
.Where(expense => dictionary.ContainsKey(espense.Lab_Id));
If you want something that can be translated to the database:
var ids = dictionary.Keys.ToList();
var query = ctx.Expenses
.Where(expense => ids.Contains(expense.Lab_Id));
Note this will only work if you have less than a few thousand keys in your dictionary, as it is translated to a SQL IN clause. If you have more than that either upload them to a temporary table and join the two tables, or pull the entire Expenses table and use the linq to objects version.

List<Expense> lstExpenses = (from l in ctx.Expenses
where report.GetLabChildren(labID, "All").Keys.Contains(i.Lab_ID)
select l).ToList<Expense>();

I'm not 100% sure what you're asking about, but looks like you're looking for ContainsKey method:
var values = report.GetLabChildren(labID, "All");
List<Expense> lstExpenses = (from l in ctx.Expenses
where values.ContainsKey(l.datLab.Lab_ID)
select l).ToList<Expense>();
I'm not sure, but there is a chance that it won't work with LINQ to Entities. Use following if it happens:
List<Expense> lstExpenses = (from l in ctx.Expenses
where values.Keys.Contains(l.datLab.Lab_ID)
select l).ToList<Expense>();

LINQ Projected Filtering C#

I want to filter my LINQ query based on an included table but am having some trouble.
Here is the original statement, which works:
return
this.ObjectContext.People.
Include("Careers").
Include("Careers.Titles").
Include("Careers.Titles.Salaries");
Now I'm trying to filter on Careers using projected filtering but am having trouble. It compiles but it leaves out the Titles and Salaries tables, which causes runtime errors, and I can't seem to add those tables back in:
var query1 = (
from c in
this.ObjectContext.People.
Include("Careers").
Include("Careers.Titles").
Include("Careers.Titles.Salaries")
select new
{
c,
Careers = from Careers in c.Careers
where Careers.IsActive == true
select Careers
});
var query = query1.AsEnumerable().Select(m => m.c);
return query.AsQueryable();
How can I include the titles and salaries tables in the filtered query?

You can simplify your query considerably, which should resolve your issue. I'm assuming that you want all people with at least 1 active career:
var query =
from c in
this.ObjectContext.People.
Include("Careers").
Include("Careers.Titles").
Include("Careers.Titles.Salaries")
where c.Careers.Any(c => c.IsActive);
return query;

I would try something like,
var query = from p in ObjectContext.People
join c in ObjectContext.Careers on p equals c.Person
where c.IsActive
select p;

C# LINQ query (MYSQL EF) - Distinct and Latest Records

I have a table, lets call it Record. Containing:
ID (int) | CustID (int) | Time (datetime) | Data (varchar)
I need the latest (most recent) record for each customer:
SQL
select * from record as i group by i.custid having max(id);
LINQ version 1
dgvLatestDistinctRec.DataSource = from g in ee.Records
group g by g.CustID into grp
select grp.LastOrDefault();
This throws an error:
System.NotSupportedException was unhandled by user code Message=LINQ
to Entities does not recognize the method 'Faizan_Kazi_Utils.Record
LastOrDefault[Record
](System.Collections.Generic.IEnumerable`1[Faizan_Kazi_Utils.Record
])' method, and this method cannot be translated into a store
expression. Source=System.Data.Entity
LINQ version 2
var list = (from g in ee.Records
group g by g.CustID into grp
select grp).ToList();
Record[] list2 = (from grp in list
select grp.LastOrDefault()).ToArray();
dgvLatestDistinctRec.DataSource = list2;
This works, but is inefficient because it loads ALL records from the database into memory and then extracts just the last (most recent member) of each group.
Is there any LINQ solution that approaches the efficiency and readability of the mentioned SQL solution?

Update:
var results = (from rec in Record group rec by rec.CustID into grp
select new
{
CustID = grp.Key,
ID = grp.OrderByDescending(r => r.ID).Select(x => x.ID).FirstOrDefault(),
Data = grp.OrderByDescending(r => r.ID).Select(x => x.Data).FirstOrDefault()
}
);
So I made a test table and wrote a Linq -> SQL Query that will do exactly what you need. Take a look at this and let me know what you think. Only thing to keep in mind if this query is scaled I believe it will run a query to the DB for each and every CustID record after the grouping in the select new. The only way to be sure would be to run SQL Tracer when you run the query for info on that go here .. http://www.foliotek.com/devblog/tuning-sql-server-for-programmers/
Original:
Could you do something like this? from g in ee.Records where g.CustID == (from x in ee.Records where (g.CustID == x.CustID) && (g.ID == x.Max(ID)).Select(r => r.CustID))
That's all pseudo code but hopefully you get the idea.

I'm probably too late to help with your problem, but I had a similar issue and was able to get the desired results with a query like this:
from g in ee.Records
group g by g.CustID into grp
from last in (from custRec in grp where custRec.Id == grp.Max(cr => cr.Id) select custRec)
select last

What if you replace LastOrDefault() with simple Last()?
(Yes, you will have to check your records table isn't empty)
Because I can't see a way how MySQL can return you "Default" group. This is not the thing that can be simply translated to SQL.

I think grp.LastOrDefault(), a C# function, is something that SQL doesn't know about. LINQ turns your query into an SQL query for your db server to understand. You might want to try and create an stored procedure instead, or another way to filter out what your looking for.
The reason your second query works is because the LINQ to SQL returns a list and then you do a LINQ query (to filter out what you need) on a C# list, which implements the IEnumerable/IQueryable interfaces and understands the grp.LastOrDefault().

I had another idea:
// Get a list of all the id's i need by:
// grouping by CustID, and then selecting Max ID from each group.
var distinctLatest = (from x in ee.Records
group x by x.CustID into grp
select grp.Max(g => g.id)).ToArray();
// List<Record> result = new List<Record>();
//now we can retrieve individual records using the ID's retrieved above
// foreach (int i in distinctLatest)
// {
// var res = from g in ee.Records where g.id == i select g;
// var arr = res.ToArray();
// result.Add(res.First());
// }
// alternate version of foreach
dgvLatestDistinctRec.DataSource = from g in ee.Records
join i in distinctLatest
on g.id equals i
select g;

Why does this additional join increase # of queries?

I'm having trouble coming up with an efficient LINQ-to-SQL query. I am attempting to do something like this:
from x in Items
select new
{
Name = x.Name
TypeARelated = from r in x.Related
where r.Type == "A"
select r
}
As you might expect, it produces a single query from the "Items" table, with a left join on the "Related" table. Now if I add another few similar lines...
from x in Items
select new
{
Name = x.Name
TypeARelated = from r in x.Related
where r.Type == "A"
select r,
TypeBRelated = from r in x.Related
where r.Type == "B"
select r
}
The result is that a similar query to the first attempt is run, followed by an individual query to the "Related" table for each record in "Items". Is there a way to wrap this all up in a single query? What would be the cause of this? Thanks in advance for any help you can provide.

The above query if written directly in SQL would be written like so (pseudo-code):
SELECT
X.NAME AS NAME,
(CASE R.TYPE WHEN A THEN R ELSE NULL) AS TypeARelated,
(CASE R.TYPE WHEN B THEN R ELSE NULL) AS TypeBRelated
FROM Items AS X
JOIN Related AS R ON <some field>
However, linq-to-sql is not as efficient, from your explanation, it does one join, then goes to individually compare each record. A better way would be to use two linq queries similar to your first example, which would generate two SQL queries. Then use the result of the two linq queries and join them, which would not generate any SQL statement. This method would limit the number of queries executed in SQL to 2.
If the number of conditions i.e. r.Type == "A" etc., are going to increase over time, or different conditions are going to be added, you're better off using a stored procedure, which would be one SQL query at all times.
Hasanain

You can use eager loading to do a single join on the server to see if that helps. Give this a try.
using (MyDataContext context = new MyDataContext())
{
DataLoadOptions options = new DataLoadOptions();
options.LoadWith<Item>(i => i.Related);
context.LoadOptions = options;
// Do your query now.
}

is there a better way to write this frankenstein LINQ query that searches for values in a child table and orders them by relevance?

I have a table of Users and a one to many UserSkills table. I need to be able to search for users based on skills. This query takes a list of desired skills and searches for users who have those skills. I want to sort the users based on the number of desired skills they posses. So if a users only has 1 of 3 desired skills he will be further down the list than the user who has 3 of 3 desired skills.
I start with my comma separated list of skill IDs that are being searched for:
List<short> searchedSkillsRaw = skills.Value.Split(',').Select(i => short.Parse(i)).ToList();
I then filter out only the types of users that are searchable:
List<User> users = (from u in db.Users
where
u.Verified == true &&
u.Level > 0 &&
u.Type == 1 &&
(u.UserDetail.City == city.SelectedValue || u.UserDetail.City == null)
select u).ToList();
and then comes the crazy part:
var fUsers = from u in users
select new
{
u.Id,
u.FirstName,
u.LastName,
u.UserName,
UserPhone = u.UserDetail.Phone,
UserSkills = (from uskills in u.UserSkills
join skillsJoin in configSkills on uskills.SkillId equals skillsJoin.ValueIdInt into tempSkills
from skillsJoin in tempSkills.DefaultIfEmpty()
where uskills.UserId == u.Id
select new
{
SkillId = uskills.SkillId,
SkillName = skillsJoin.Name,
SkillNameFound = searchedSkillsRaw.Contains(uskills.SkillId)
}),
UserSkillsFound = (from uskills in u.UserSkills
where uskills.UserId == u.Id && searchedSkillsRaw.Contains(uskills.SkillId)
select uskills.UserId).Count()
} into userResults
where userResults.UserSkillsFound > 0
orderby userResults.UserSkillsFound descending
select userResults;
and this works! But it seems super bloated and inefficient to me. Especially the secondary part that counts the number of skills found.
Thanks for any advice you can give.
--r

I think that should do the trick:
(from u in users
where u.UserSkills.Any(skill => searchedSkillsRaw.Contains(skill.SkillId))
select new
{
u.Id,
u.FirstName,
u.LastName,
u.UserName,
UserPhone = u.UserDetail.Phone,
UserSkills = u.UserSkills,
UserSkillsFound = u.UserSkills.Where(skill => searchedSkillsRaw.Contains(skill.SkillId)).Count()
} into userResults
orderby userResults.UserSkillsFound descending
select userResult).ToList();
However, since this is a query that gets executed on SQL server I strongly recommend to remove the 'ToList()' call from the first query. Because that actually causes LINQ to run two separate queries on the SQL server. You should change it to IQueryable instead. The power of LINQ is to construct queries in several steps without having to actually execute it in between. So 'ToList' should be called only at the end when the entire query has been constructed. In fact what you currently do is running the second query in memory rather than on the database server.
In regards to your UserSkills one-to-many relation you do not need to do an explicity join in LINQ. You can just access the collection property instead.
Let me know if you need more explanation.
Michael

Why not just let people do, say, fUsers.UserSkills.Count()? It would reduce the amount of data retrieved from the server in the first place.
Alternatively, you could create a View that has a calculated field in it and then map that to a type. Would push the query for count down into the DB.