I have the following query to start with:
var query = from p in db.Products
from pc in p.NpProductCategories
where pc.CategoryId == categoryId
select p;
I'm applying some more filtering on it and in the end I want to sort the results:
if (orderBy == ProductSortingEnum.Name)
query = query.OrderBy(x => x.Name);
else
query = query.OrderBy(............);
My big problem (coming from not knowing linq too good) is the ELSE here. How can I sort results by a column that is not in the current result set? I would like to somehow link to another linq query in the orderby. The sorting I'm trying to achive is to link to NpProductVariants query using the ProductId to match between NpProductVariant and Products
and sort by the Price of the NpProductVariant
Assuming you have the relationship set up in the dbml...
For one to one (and many to one):
query = query.OrderBy(p => p.NpProductVariant.Price);
For one to many:
query = query.OrderBy(p => p.NpProductVariants.Select(v => v.Price).Max());
Also:
var query =
from p in db.Products
where p.NpProductCategories.Any(pc => pc.CategoryId == categoryId)
select p;
I think you can hook your Join to your query as long as it is returning the same thing. So maybe something like (I'm not 100 % sure since I haven't tried it):
query = from i1 in query
join i2 in query2 on i1.PropertyToJoin equals i2.PropertyToJoin
orderby i1.OrderProp1, i2.OrderProp2
select i1;
But I think it might be a good idea to check the generated sql so it is still effective.
Related
I want to get the latest record of each group from a SQL Server table using Linq.
Table Example:
I want to get this result:
My Linq query returns one record for each company, but it doesn't return the most recent ones:
var query = from p in db.Payments
where p.Status == false
&& DateTime.Compare(DateTime.Now, p.NextPaymentDate.Value) == 1
group p by p.CompanyID into op
select op.OrderByDescending(nd => nd.NextPaymentDate.Value).FirstOrDefault();
What am i missing here? Why isn't the NextPaymentDate being ordered correctly?
!!UPDATE!!
My query is working as expected. After analysing #Gilang and #JonSkeet comments i ran further tests and found that i wasn't getting the intended results due to a column that wasn't being updated.
var query = from p in db.Payments
where p.Status == false
group p by p.CompanyID into op
select new {
CompanyID = op.Key,
NextPaymentDate = op.Max(x => x.NextPaymentDate),
Status = false
};
The reason your query is not being ordered correctly is that your query does not do proper grouping. You did correctly grouping by CompanyID, but then you have to retrieve the maximum NextPaymentDate by calling aggregate function.
Status can be assigned false because it is already filtered by Where clause in the early clauses.
I have the following linq-to-entities query with 2 joined tables that I would like to add pagination to:
IQueryable<ProductInventory> data = from inventory in objContext.ProductInventory
join variant in objContext.Variants
on inventory.VariantId equals variant.id
where inventory.ProductId == productId
where inventory.StoreId == storeId
orderby variant.SortOrder
select inventory;
I realize I need to use the .Join() extension method and then call .OrderBy().Skip().Take() to do this, I am just gettting tripped up on the syntax of Join() and can't seem to find any examples (either online or in books).
NOTE: The reason I am joining the tables is to do the sorting. If there is a better way to sort based on a value in a related table than join, please include it in your answer.
2 Possible Solutions
I guess this one is just a matter of readability, but both of these will work and are semantically identical.
1
IQueryable<ProductInventory> data = objContext.ProductInventory
.Where(y => y.ProductId == productId)
.Where(y => y.StoreId == storeId)
.Join(objContext.Variants,
pi => pi.VariantId,
v => v.id,
(pi, v) => new { Inventory = pi, Variant = v })
.OrderBy(y => y.Variant.SortOrder)
.Skip(skip)
.Take(take)
.Select(x => x.Inventory);
2
var query = from inventory in objContext.ProductInventory
where inventory.ProductId == productId
where inventory.StoreId == storeId
join variant in objContext.Variants
on inventory.VariantId equals variant.id
orderby variant.SortOrder
select inventory;
var paged = query.Skip(skip).Take(take);
Kudos to Khumesh and Pravin for helping with this. Thanks to the rest for contributing.
Define the join in your mapping, and then use it. You really don't get anything by using the Join method - instead, use the Include method. It's much nicer.
var data = objContext.ProductInventory.Include("Variant")
.Where(i => i.ProductId == productId && i.StoreId == storeId)
.OrderBy(j => j.Variant.SortOrder)
.Skip(x)
.Take(y);
Add following line to your query
var pagedQuery = data.Skip(PageIndex * PageSize).Take(PageSize);
The data variable is IQueryable, so you can put add skip & take method on it. And if you have relationship between Product & Variant, you donot really require to have join explicitly, you can refer the variant something like this
IQueryable<ProductInventory> data =
from inventory in objContext.ProductInventory
where inventory.ProductId == productId && inventory.StoreId == storeId
orderby inventory.variant.SortOrder
select new()
{
property1 = inventory.Variant.VariantId,
//rest of the properties go here
}
pagedQuery = data.Skip(PageIndex * PageSize).Take(PageSize);
My answer here based on the answer that is marked as true
but here I add a new best practice of the code above
var data= (from c in db.Categorie.AsQueryable().Join(db.CategoryMap,
cat=> cat.CategoryId, catmap => catmap.ChildCategoryId,
cat, catmap) => new { Category = cat, CategoryMap = catmap })
select (c => c.Category)
this is the best practice to use the Linq to entity because when you add AsQueryable() to your code; system will converts a generic System.Collections.Generic.IEnumerable to a generic System.Linq.IQueryable which is better for .Net engine to build this query at run time
thank you Mr. Khumesh Kumawat
You would simply use your Skip(itemsInPage * pageNo).Take(itemsInPage) to do paging.
I'm having a bit trouble with a query in Linq to Entities which I hope someone can shed a light on :-) What I'm trying to do is to create a query that joins three tables.
So far it works, but since the last table I'm trying to join is empty, the result of the query doesn't contain any records. When I remove the last join, it gives me the right results.
My query looks like this:
var query = from p in db.QuizParticipants
join points in db.ParticipantPoints on p.id
equals points.participantId into participantsGroup
from po in participantsGroup
join winners in db.Winners on p.id
equals winners.participantId into winnersGroup
from w in winnersGroup
where p.hasAttended == 1 && p.weeknumber == weeknumber
select new
{
ParticipantId = p.id,
HasAttended = p.hasAttended,
Weeknumber = p.weeknumber,
UmbracoMemberId = p.umbMemberId,
Points = po.points,
HasWonFirstPrize = w.hasWonFirstPrize,
HasWonVoucher = w.hasWonVoucher
};
What I would like is to get some records even if the Winners table is empty or there is no match in it.
Any help/hint on this is greatly appreciated! :-)
Thanks a lot in advance.
/ Bo
If you set these up as related entities instead of doing joins, I think it will be easier to do what you're trying to do.
var query = from p in db.QuizParticipants
where p.hasAttended == 1 && p.weeknumber == weeknumber
select new
{
ParticipantId = p.id,
HasAttended = p.hasAttended,
Weeknumber = p.weeknumber,
UmbracoMemberId = p.umbMemberId,
Points = p.ParticipantPoints.Sum(pts => pts.points),
HasWonFirstPrize = p.Winners.Any(w => w.hasWonFirstPrize),
HasWonVoucher = p.Winners.Any(w => w.hasWonVoucher)
};
This is assuming hasWonFirstPrize and hasWonVoucher are boolean fields, but you can use any aggregate function to get the results you need, such as p.Winners.Any(w => w.hasWonFirstPrize == 1)
I don't use query syntax a lot but I believe you need to change from w in winnersGroup to from w in winnersGroup.DefaultIfEmpty()
I had tried to join two table conditionally but it is giving me syntax error. I tried to find solution in the net but i cannot find how to do conditional join with condition. The only other alternative is to get the value first from one table and make a query again.
I just want to confirm if there is any other way to do conditional join with linq.
Here is my code, I am trying to find all position that is equal or lower than me. Basically I want to get my peers and subordinates.
from e in entity.M_Employee
join p in entity.M_Position on e.PostionId >= p.PositionId
select p;
You can't do that with a LINQ joins - LINQ only supports equijoins. However, you can do this:
var query = from e in entity.M_Employee
from p in entity.M_Position
where e.PostionId >= p.PositionId
select p;
Or a slightly alternative but equivalent approach:
var query = entity.M_Employee
.SelectMany(e => entity.M_Position
.Where(p => e.PostionId >= p.PositionId));
Following:
from e in entity.M_Employee
from p in entity.M_Position.Where(p => e.PostionId >= p.PositionId)
select p;
will produce exactly the same SQL you are after (INNER JOIN Position P ON E..PostionId >= P.PositionId).
var currentDetails = from c in customers
group c by new { c.Name, c.Authed } into g
where g.Key.Authed == "True"
select g.OrderByDescending(t => t.EffectiveDate).First();
var currentAndUnauthorised = (from c in customers
join cd in currentDetails
on c.Name equals cd.Name
where c.EffectiveDate >= cd.EffectiveDate
select c).OrderBy(o => o.CoverId).ThenBy(o => o.EffectiveDate);
If you have a table of historic detail changes including authorisation status and effective date. The first query finds each customers current details and the second query adds all subsequent unauthorised detail changes in the table.
Hope this is helpful as it took me some time and help to get too.
I have some Linq code and it's working fine. It's a query that has a subquery in the Where clause. This subquery is doing a groupby. Works great.
The problem is that I don't know how to grab one of the results from the subquery out of the subquery into the parent.
Frst, here's the code. After that, I'll expplain what piece of data i'm wanting to extract.
var results = (from a in db.tblProducts
where (from r in db.tblReviews
where r.IdUserModified == 1
group r by
new
{
r.tblAddress.IdProductCode_Alpha,
r.tblAddress.IdProductCode_Beta,
r.tblAddress.IdProductCode_Gamma
}
into productGroup
orderby productGroup.Count() descending
select
new
{
productGroup.Key.IdProductCode_Alpha,
productGroup.Key.IdProductCode_Beta,
productGroup.Key.IdProductCode_Gamma,
ReviewCount = productGroup.Count()
}).Take(3)
.Any(
r =>
r.IdProductCode_Alpha== a.IdProductCode_Alpha&&
r.IdProductCode_Beta== a.IdProductCode_Beta&&
r.IdProductCode_Gamma== a.IdProductCode_Gamma)
where a.ProductFirstName == ""
select new {a.IdProduct, a.FullName}).ToList();
Ok. I've changed some field and tables names to protect the innocent. :)
See this last line :-
select new {a.IdProduct, a.FullName}).ToList();
I wish to include in that the ReviewCount (from the subquery). I'm jus not sure how.
To help understand the problem, this is what the data looks like.
Sub Query
IdProductCode_Alpha = 1, IdProductCode_Beta = 2, IdProductCode_Gamma = 3, ReviewCount = 10
... row 2 ...
... row 3 ...
Parent Query
IdProduct = 69, FullName = 'Jon Skeet's Wonder Balm'
So the subquery grabs the actual data i need. The parent query determines the correct product, based on the subquery filters.
EDIT 1: Schema
tblProducts
IdProductCode
FullName
ProductFirstName
tblReviews (each product has zero to many reviews)
IdProduct
IdProductCode_Alpha (can be null)
IdProductCode_Beta (can be null)
IdProductCode_Gamma (can be null)
IdPerson
So i'm trying to find the top 3 products a person has done reviews on.
The linq works perfectly... except i just don't know how to include the COUNT in the parent query (ie. pull that result from the subquery).
Cheers :)
Got it myself. Take note of the double from at the start of the query, then the Any() being replaced by a Where() clause.
var results = (from a in db.tblProducts
from g in (
from r in db.tblReviews
where r.IdUserModified == 1
group r by
new
{
r.tblAddress.IdProductCode_Alpha,
r.tblAddress.IdProductCode_Beta,
r.tblAddress.IdProductCode_Gamma
}
into productGroup
orderby productGroup.Count() descending
select
new
{
productGroup.Key.IdProductCode_Alpha,
productGroup.Key.IdProductCode_Beta,
productGroup.Key.IdProductCode_Gamma,
ReviewCount = productGroup.Count()
})
.Take(3)
Where(g.IdProductCode_Alpha== a.IdProductCode_Alpha&&
g.IdProductCode_Beta== a.IdProductCode_Beta&&
g.IdProductCode_Gamma== a.IdProductCode_Gamma)
where a.ProductFirstName == ""
select new {a.IdProduct, a.FullName, g.ReviewCount}).ToList();
While I don't understand LINQ completely, but wouldn't the JOIN work?
I know my answer doesn't help but it looks like you need a JOIN with the inner table(?).
I agree with shahkalpesh, both about the schema and the join.
You should be able to refactor...
r => r.IdProductCode_Alpha == a.IdProductCode_Alpha &&
r.IdProductCode_Beta == a.IdProductCode_Beta &&
r.IdProductCode_Gamma == a.IdProductCode_Gamma
into an inner join with tblProducts.