This question already has answers here:
Linq-to-Entities Join vs GroupJoin
(3 answers)
Closed 1 year ago.
There are 0 to n departments in my company, 0 to n offices in 1 department, and 0 to n emplyees in 1 office.Now I need a query using linq to list emplyees's average age by department, if nobody in a department then default average is 0.
code is below:
DataContext ctx = new DataContext();
var q0 = from d in ctx.Departments
join o in ctx.Offices on d.Id equals o.DepartmentId
join e in ctx.Employees on o.Id equals e.OfficeId
group e by d into de
select new {
DepartmentId = de.Key.Id,
AverageAge = de.Count() == 0 ? 0 : de.Average(e => e.Age),
};
var q1 = from d in ctx.Departments
join de in q0 on d.Id equals de.DepartmentId into des
from de in des.DefaultIfEmpty()
select new
{
DepartmentName = d.Name,
AverageAge = de == null ? 0 : de.AverageAge
};
var result = q1.ToList();
foreach (var item in result)
{
Console.WriteLine("{0}-{1}", item.DepartmentName, item.AverageAge);
}
ctx.Dispose();
But how to combine q0 and q1 to one query?
Were you meaning something along the lines of:
var newQ2 = from d in ctx.Departments
outer left join o in ctx.Offices on d.Id equals o.DepartmentId
outer left join e in ctx.Employees on o.Id equals e.OfficeId
group e by d into de
select new {
DepartmentId = de.Key.Id,
AverageAge = de.Count() == 0 ? 0 : de.Average(e => e.Age),
};
Changed to:
var newQ2 = from d in ctx.Departments
join o in ctx.Offices on d.Id equals o.DepartmentId
join e in ctx.Employees on o.Id equals e.OfficeId
group e by d into de.DefaultIfEmpty()
select new {
DepartmentId = de.Key.Id,
DepartdentName = select d.Name from d where d.id = de.Key.Id,
AverageAge = de.Count() == 0 ? 0 : de.Average(e => e.Age),
};
Addendum: I would use a sub-select to match up the extra name, not knowing your db layout I have improvised from your code, but you could make it more efficient and have a multipart join based on sub-selects as well. Sorry I cant test this code out at work, I can approximate fairly well, but would need some more info on where your department names are located if you need a more detailed answer:) I have changed the outer left joins back to joins, sorry I forgot in C# with linq you can use DefaultIfEmpty() to cause outer left join behaviour in code.
An outer left join will return nulls where there are no corresponding values, but will allow returns on any parts that do have a corresponding value. Join however will not return any null entries which I suspect is why you had the two queries?
The only caveat on the query I have presented is that you will need to infill any values you require before you use them if they are nulls, for example DepartmentId will need some logic to populate it in case DE is null.
Thank you all，I have got the answer:
var q1 =
from d in ctx.Departments
from o in ctx.Offices.Where(o => o.DepartmentId == d.Id).DefaultIfEmpty()
from e in ctx.Employees.Where(e => e.OfficeId == o.Id).DefaultIfEmpty()
group e by d into de
select new {
DepartmentName = de.Key.Name,
AverageAge = de.Average(e => e == null ? 0 : e.Age),
};
Related
Running into a bit of trouble with my Linq Query. I'm attempting to join several tables and construct a new viewmodel to return to the details page, but running into a bit of a misunderstanding or incorrect syntax.
I have a details page for loads, but I want to include associated data from the trucks table which is joined through a linking table, load_trucks. Below is what I have right now, but is clearly incorrect.
var query = (from l in dbContext.Loads
where l.Id == id
join lt in dbContext.LoadTrucks on l.Id equals lt.LoadId into LoadTrucks
from lt in LoadTrucks.DefaultIfEmpty()
join t in dbContext.Trucks on lt.TruckId equals t.Id into Trucks
where Trucks.All(trk => LoadTrucks.All(ldtrk => ldtrk.TruckId == trk.Id))
from t in Trucks.DefaultIfEmpty()
join u in dbContext.Users on l.UserId equals u.Id into Users
where Users.All(usr => usr.Id == l.UserId)
from u in Users.DefaultIfEmpty()
join u2 in dbContext.Users on l.CreatedBy equals u2.Id into Users2
from u2 in Users2.DefaultIfEmpty()
join dr in dbContext.DriverReceipts on l.Id equals dr.LoadId into DriverReceipts
where DriverReceipts.All(drR => drR.LoadId == l.Id)
from dr in DriverReceipts.DefaultIfEmpty()
join le in dbContext.LogEntries on l.Id equals le.LoadId into LogEntries
where LogEntries.All(lgE => lgE.LoadId == l.Id)
from le in LogEntries.DefaultIfEmpty()
select new LoadsViewModel()
{
Id = l.Id,
LoadId = l.LoadTag ?? l.Id.ToString(),
LoadCreatedBy = u2.FullName,
TruckList = Trucks.ToList(),
UserList = Users.ToList(),
DriverLogEntries = LogEntries.ToList(),
ReceiptList = DriverReceipts.ToList()
});
Any help on this would be great. Thanks!
You need to add :
.FirstOrDefault();
at the end of your query.
That will effectively materialize your query to a single instance of:
LoadsViewModel
You could also wait until the last moment to call .FirstOrDefault() just before where you actually need it.
Currently, I am executing two queries based upon whether w.Type is either 1 or 2. If w.Type is 1 we perform a join to the Issues table and if the Type is 2 we join to the TSubs table. I am trying to merge these queries into one.
var productIdOne = (from w in listAbandonedCarts
join i in Issues on w.ProductId equals i.Id
where w.Type == 1
select new { i.Title.Name }).ToList();
var productIdTwo = (from w in listAbandonedCarts
join ts in TSubs on w.ProductId equals ts.Id
where w.Type == 2
select new { ts.Title.Name }).ToList();
I am considering using two left outer joins based upon this SQL psuedo-code
SELECT*
FROM P_carts pc
LEFT OUTER tSubs ts on ts.id = pc.productid and pc.Type = 2
LEFT OUTER issues i on i.id = pc.productid and pc.Type = 1
So far i have some linq pseudo coded but i'm struggling to get the syntax correct for the two conditional joins
var listProducts = (from w in listAbandonedCarts
join i in Issues on w.ProductId equals i.Id into iN && w.ProductId == 1
from i in iN.DefaultIfEmpty()
join into ts in TSubs.....
The problem I'm struggling with is that this isn't a double left outer its two separate joins. My current error is that i cannot have w.ProductId after the equals because I'm out of scope of w at this point and can't figure out how to structure the linq statement. Any help would be much appreciated, thanks!
Give this a shot:
var productIds = (
from w in listAbandonedCarts
from i in Issues.Where(issue => issue.Id == w.ProductId && w.Type == 1).DefaultIfEmpty()
from t in TSubs.Where(tsub => tsub.Id == w.ProductId && w.Type == 2).DefaultIfEmpty()
select new {Name = (w.Type == 1 ? i.Title.Name : t.Title.Name)})
.ToList();
var listProducts = (from w in listAbandonedCarts
join i in Issues on w.ProductId equals i.Id && w.ProductId == 1 into iN
from i in iN.DefaultIfEmpty()
join into ts in TSubs on ts.id equals pc.productid into tsBag
from ts in tsBag.DefaultIfEmpty()
select new
{
// All columns you need
};
Please try the above linq. This sample code is not compiled nor tested. Please use this for reference purpose only.
So I have a SQL view that I've created that provides me what I need. Essentially it's a job position billeting system that shows how many positions have been authorized vs filled (or assigned).
SELECT Companies.Name AS Company, Grades.Name AS Grade, Series.Name
AS Series, Positions.Authorized, COUNT(People.PersonId) AS Assigned
FROM Companies INNER JOIN
Positions ON Companies.Id = Positions.CompanyId INNER JOIN
Series ON Positions.SeriesId = Series.Id INNER JOIN
Grades ON Positions.GradeId = Grades.Id INNER JOIN
People ON Positions.CompanyId = People.CompanyId AND
Positions.SeriesId = People.SeriesId AND Positions.GradeId = People.GradeId
GROUP BY Companies.Name, Grades.Name, Series.Name, Positions.Authorized
Now what I'd like to be able to do is recreate this in a LINQ query. I've almost got it where I need it; however, I can't figure out how to add the counted column at the end that's based on the People table.
Here's my current LINQ query:
var query = from a in db.Companies
join b in db.Positions on a.Id equals b.CompanyId
join c in db.Series on b.SeriesId equals c.Id
join d in db.Grades on b.GradeId equals d.Id
join e in db.People on new { b.CompanyId, b.SeriesId, b.GradeId } equals new { e.CompanyId, e.SeriesId, e.GradeId }
group a by new { CompanyName = a.Name, GradeName = d.Name, SeriesName = c.Name, b.Authorized, e.PersonId } into f
select new { Company = f.Key.CompanyName, Grade = f.Key.GradeName, Series = f.Key.SeriesName, f.Key.Authorized, Assigned = /* needs to be Count(People.PersonId) based on last join */ )};
Thanks in advance for any help you can provide!
Figured it out. The reason why it was posting multiple rows and not doing a proper count on the same row was because in my "group by" I added in "e.PersonId" when it should have simply been removed. I also had to add a few things to make it work on the front-end razor views since it's an anonymous type (this doesn't have anything to do with the original question, but thought I'd give reason to the changes). So the person who removed their answer, you were partially right, but the reason it wasn't working was because of the additional fieldin the group by:
dynamic query = (from a in db.Companies
join b in db.Positions on a.Id equals b.CompanyId
join c in db.Series on b.SeriesId equals c.Id
join d in db.Grades on b.GradeId equals d.Id
join e in db.People on new { b.CompanyId, b.SeriesId, b.GradeId } equals new { e.CompanyId, e.SeriesId, e.GradeId }
group a by new { CompanyName = a.Name, GradeName = d.Name, SeriesName = c.Name, b.Authorized } into f
select new { Company = f.Key.CompanyName, Grade = f.Key.GradeName, Series = f.Key.SeriesName, Authorized = f.Key.Authorized, Assigned = f.Count()}).AsEnumerable().Select(r => r.ToExpando());
And what it looks like on the page:
I am using LINQ query to get the rows with certain conditions. Here is the query.
var query = from v in dt1.AsEnumerable()
join c in dt2.AsEnumerable() on v.Field<int>("ID") equals c.Field<int>("ID")
where v.Field<string>("col1").Equals("abcd")
&& (c.Field<string>("col1").Equals("8776") || c.Field<string>("col1").Equals("8775"))
select new
{
ok = (from a in v where v.Field<string>("stah").Equals("1") select a).count(),
ok1 = (from a in v where v.Field<string>("stah").Equals("2") select a).count(),
ok2 = (from a in v where v.Field<string>("stah").Equals("3") select a).count()
};
The error is present in
ok = (from a in v where v.Field<string>("stah").Equals("1") select a).count()
The error is
could not find an implementation of the query pattern for source type
'system.data.DataRow'. 'Where' not found
Sample Input :
dt1
iD col1 stah
1 4567 1
2 8748 2
3 3487 3
4 8776 1
dt2
iD col1
1 4754
2 4576
Output
Get count of all rows where stah=1 && dt2.col1='4754'
But I cannot get it working. What is the correct syntax for this ?
If I have understood you correctly, then this is what you need:-
var query = dt1.AsEnumerable()
.Where(x => x.Field<int>("stah") == 1
&& dt2.AsEnumerable()
.Any(z => z.Field<int>("Id") == x.Field<int>("Id")
&& z.Field<string>("Col1") == "4754")
).Count();
#HarshitShrivastava mentioned that my previous attempt at the query didn't take into account all the where conditions.
How about this version using a mix of Linq query and Linq Lambda:
var query = from dataRows1 in dt1.AsEnumerable().Where(r => r.Field<string>("col1").Equals("abcd"))
join dataRows2 in dt2.AsEnumerable().Where(r => r.Field<string>("col1").Equals("8776") || r.Field<string>("col1").Equals("8775"))
on dataRows1.Field<int>("ID") equals dataRows2.Field<int>("ID") into b
select new
{
id = dataRows1.Field<int>("ID"),
ok = (from a in b where a.Field<string>("stah").Equals("1") select a).Count(),
ok1 = (from a in b where a.Field<string>("stah").Equals("2") select a).Count(),
ok2 = (from a in b where a.Field<string>("stah").Equals("3") select a).Count()
};
Note: I included the ID field in the projected output just for verifying the results. Remove as needed.
I am trying to write a query that grabs information from one database and joins it to information in a different database.
TableA
idA
valueA
idB
TableB
idB
valueB
The tricky part is that in TableA, idB isn't always defined, so when I do a normal join, I only get results where TableA has a idB value. What I want is to be able to grab all of the information from TableA even if it doesn't have a corresponding idB value.
Here is a query expression syntax version of the left join to follow up on tvanfosson's answer.
var query = from rowA in db.TableA
join rowB in db.TableB
on rowA.idB equals rowB.idB into b
from item in b.DefaultIfEmpty()
select new
{
idA = rowA.idA,
valueA = rowA.valueA,
idB = rowA.idB,
valueB = item != null ? item.valueB : 0 // or other default value
};
Use a left outer join by checking if the value returned from the right hand side is null and supplying a default value for that case.
var q = db.TableA.Join( db.TableA,
a => a.idB,
b => b.idB,
(a,b) => new
{
A = a.ValueA,
B = b == null ? null : b.ValueB
});
You can do a left outer join in LINQ with SelectMany (directly calling Queryable methods) or in comprehension syntax join ... into:
var results = from a in db.TableA
join b in db.TableB on a.idB equals b.idB
into found
select new {
A = a,
Bs = found
};
In the output Bs will be IEnumerable<typeof-db-TableB>
Left Join Example:
var leftOuterJoinQuery =
from category in categories
join prod in products on category.ID equals prod.CategoryID into prodGroup
from item in prodGroup.DefaultIfEmpty(new Product{Name = String.Empty, CategoryID = 0})
select new { CatName = category.Name, ProdName = item.Name };