I am trying to get from 3 related tables by using LINQ. But when I use 2 joins, the result takes only elements getting from 2nd join. Here is my code:
var myAssList = mldb.Assigns
.Join(mldb.Lists,
a => a.list_id,
l => l.id,
(a, l) => new {
Assign = a,
List = l
})
.Where(a => a.Assign.assigned_to == "myname")
.Join(mldb.Elements,
li => li.List.id,
e => e.parent_server_id,
(li, e) => new {
Element = e
});
var jsonSerialiser = new JavaScriptSerializer();
var listListJson = jsonSerialiser.Serialize(myAssList);
this Json return only attributes from Element(e) and List(li). But I want to get also the attributes from Assign(a).
The SQL query I am trying to realize in LINQ is that:
select * from Assigns
inner join Lists
on Assigns.server_list_id=Lists.id
inner join Elements
on Lists.id=Elements.parent_id
where Assigns.assigned_to='myname'
So, how can I get the attributes from the first join also (from "a", "l" and "e")?
You can access Assign entity from outer sequence li variable:
.Join(mldb.Elements,
li => li.List.id,
e => e.parent_server_id,
(li, e) => new {
Element = e,
Assign = li.Assign // here
});
from a in mldb.Assigns
join l in mldb.Lists on a.list_id equals l.id
join e in mldb.Elements on l.id equals e.parent_server_id
where a => a.Assign.assigned_to == "myname"
select new { Assign = a, Element = e }
This is so called "query syntax". It makes LINQ expressions looks like SQL queries.
In the end they are translated to IEnumerable extension methods. If you want
to join multiple tables then query syntax is more readable. Another useful feature
of query syntax is let clause. With the aid of it, you can declare additional variables
inside your queries.
Related
I'm trying to convert my SQL statement to a Linq statement and I'm not sure how to add the second COUNT to it. This is my SQL statement
SELECT l.Campus_Name, Labs = COUNT(*), LabsWithSubnets = COUNT(s.Lab_Space_Id)
FROM vw_Lab_Space l
LEFT JOIN vw_Subnet s on l.Lab_Space_Id = s.Lab_Space_Id
GROUP BY l.Campus_Name
ORDER BY 1
and this is my LINQ statement so far:
from l in Vw_Lab_Space
from s in Vw_Subnet
.Where(s => s.Lab_Space_Id == l.Lab_Space_Id)
.DefaultIfEmpty() // <=- triggers the LEFT JOIN
group l by new { l.Campus_Name } into g
orderby g.Key.Campus_Name
select new {
Campus_Name = g.Key.Campus_Name,
Labs = g.Count()
}
So I have everything but the LabsWithSubnets part in there. I'm just not sure how to add that in as I can't just do an s.Lab_Space_id.Count() in the select statement.
If you need table structure and sample data please see Need help creating an OUTER JOIN to count spaces.
Using your query as a basis, you need the groups to include s so you can count when non-null (I also removed the unnecessary anonymous object around the grouping key):
from l in Vw_Lab_Space
from s in Vw_Subnet
.Where(s => s.Lab_Space_Id == l.Lab_Space_Id)
.DefaultIfEmpty() // <=- triggers the LEFT JOIN
group new { l, s } by l.Campus_Name into g
orderby g.Key
select new {
Campus_Name = g.Key,
Labs = g.Count(),
LabsWithSubnets = g.Count(ls => ls.s != null)
}
However, rather than translate the SQL, I would probably take advantage of LINQ's group join to handle the query slightly differently:
var ans = from l in Vw_Lab_Space
join s in Vw_Subnet on l.Lab_Space_Id equals s.Lab_Space_Id into sj
group new { l, sj } by ls.Campus_Name into lsjg
select new {
Campus_Name = lsjg.Key,
NumLabs = lsjg.Count(),
LabsWithSubnets = lsjg.Sum(lsj => lsj.sj.Count())
};
PS Even in your query, I would use join...from...DefaultIfEmpty rather than from...from...where but depending on your database engine, may not matter.
I'm having trouble getting my Linq statemnt to work when doing an outer join and a group by. Here's a SQL version of what I'm trying to accomplish:
select p.PRIMARY_KEY, min(p.EFFECTIVE_DATE), sum(IsNull(c.PAID_INDEMNITY, 0))
from PRMPOLCY p
left outer join CLMMAST c on p.PRIMARY_KEY = c.POLICY_NO
where p.UNDERWRITER_UID = 93
GROUP BY p.PRIMARY_KEY
Here's what I have in Linq (which doesn't work):
var result = from p in context.PRMPOLCies
join c in context.CLMMASTs on p.PRIMARY_KEY equals c.POLICY_NO into polClm
where (p.UNDERWRITER_UID == underwriter)
from grp in polClm.DefaultIfEmpty()
group grp by p.PRIMARY_KEY into g
select new PolicySummation()
{
PolicyNo = g.Key,
Incurred = g.Sum(grp => grp.PAID_INDEMNITY ),
EffDate = g.Min(grp => grp.PRMPOLCY.EFFECTIVE_DATE
};
Beating my head against the wall trying to figurwe this out!
Assuming you have a navigation property set up between PRMPOLCY and CLMMAST, you shouldn't need to specify the join explicitly. It's much easier to express most queries in linq without explicit joins, but rather treating your structures as a hierarchy. I don't know the specifics of your model property names, but I'd take a guess that something like this would work.
var result =
from p in context.PRMPOLCies
where (p.UNDERWRITER_UID == underwriter)
select new PolicySummation {
PolicyNo = p.PRIMARY_KEY,
Incurred = p.CLMASTs.Select(c => c.PAID_INDEMNITY).DefaultIfEmpty().Sum(),
EffDate = p.EFFECTIVE_DATE,
};
You need to include both your tables in the group clause like this:
group new { p, grp } by p.PRIMARY_KEY into g
Then in your Sum / Min
g.Sum(grp => grp.grp == null ? 0 : grp.grp.PAID_INDEMNITY )
g.Min(grp => grp.p.PRMPOLCY.EFFECTIVE_DATE)
I am using lambda expression to build a query and I got stuck in a situation where I have to apply join with 2 tables but it will be based on a parameter like if parameter "status=1" then join must be apply between 2 tables and if "status=0" then no join required to be apply there.
How it is possible to apply join based on some parameter?
Please remember I don't want to rewrite query 2 times with if and else conditions. I need to do this with single query.
Below is my query:
db.Users.AsQueryable().AsExpandable().Where(featuredUserPredicate)
.GroupJoin(db.UserProfile, u => u.UserID, up => up.UserID, (u, up) => new { Users = u, UserProfile = up })
.SelectMany(s => s.UserProfile.DefaultIfEmpty().AsEnumerable(), (s, up) => new { s, up })
.GroupJoin(db.ProjectReview, u => u.s.Users.UserID, pr => pr.ReviewForUserId, (u, pr) => new
{
u,
pr
}).SelectMany(s => s.pr.DefaultIfEmpty().AsEnumerable(), (s, pr) => new
{
s.u,
Rate = pr == null ? 0 : pr.Rate
}).GroupBy(g => new { g.u.s.Users }).Select(r => new
{
key = r.Key.Users.UserID,
name = r.Key.Users,
sum = r.Sum(l => l.Rate)
}))
In above query I want to add one more join from "usercategory" table but this join will be based on "status" value. If value of "status=1" then join will apply otherwise this query will run as is.
You can create your query object like this.
var query = context.MyTable; //main query
query = status == 1 ? query.Join() : query; //apply join conditionally
query = query.Where() // more expressions, might also need conditions here
query = query.Skip().Take() // apply your paging here
var result = query.ToList();// this is where the query will be executed.
Microsoft has this help page for performing a left outer join, however it's in linq query syntax. What's the equivalent to this, using method syntax?
http://msdn.microsoft.com/en-us/library/bb397895.aspx
For example, I have two enumerables:
class TA {string Name{get;}}
class TB {string Name{get;}}
Enumerable<TA> A;
Enumerable<TB> B;
The result I want is this:
var joined =
A.Select(a => new
{ left = a,
right = B.FirstOrDefault(b => b.Name == a.Name)
});
This gives me what I need with just select and (effectively) a nested select. Perhaps this isn't an actual left outer join...
I've used something like
var q = (from a in db.Item1Set
from b in db.Item2Set.Where(i2 => i2.Item1Id == a.Id).DefaultIfEmpty());
I want to know how to make Linq expression that has the same effect as these SQL query
SELECT item.*, priceforitem.*
FROM
item
LEFT JOIN priceforitem
ON priceforitem.ItemID = item.ItemID
AND priceforitem.PriceID = ?PriceID
I already make it using the Method query but I don't know if it will produce the same result
db.Items
.GroupJoin(
db.PriceForItems.Where(pi => pi.PriceID == id),
i => i.ItemID,
pi => pi.ItemID,
(i, pi) => new { Item = b, Prices = pi })
.SelectMany(
a => a.Prices.DefaultIfEmpty(),
(i, pi) => new
{
ItemID = i.Item.ItemID,
Code = i.Item.Code,
Name = i.Item.Name,
PriceForItemID = pi.PriceForItemID,
Price = pi.Price
})
and then after thinking for awhile i shorten it like this
db.Items
.SelectMany(
i => db.PriceForItems.Where(
pi => pi.PriceID == id
&& pi.ItemID = i.ItemID).DefaultIfEmpty(),
(i, pi) => new
{
ItemID = i.Item.ItemID,
Code = i.Item.Code,
Name = i.Item.Name,
PriceForItemID = pi.PriceForItemID,
Price = pi.Price
})
I am new to Linq, and I don't know which is better and how to convert it to Linq query statement.
First of all your sql query. It is effectively and inner join because the where condition will filter out all rows where data from priceforitem is null. If you do want to convert same query to linq you can do it like
from i in db.Items
join p in db.PriceforItems on
i.ItemId equals p.ItemId into tempvals
from t in tempvals.DefaultIfEmpty()
where t.PriceId == id
select new{i.ItemId, ..., t.PriceId, t...., t....}
I mostly write linq queries instead of expressions where they are more readable to me. If you still want to get an expression, you can write a valid linq query and paste it into Linqpad and it will give the result as well as lambda expression of your query.