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Multiple joins with multiple on statements using Linq Lambda expressions [duplicate]

Suppose I have a list of {City, State}. It originally came from the database, and I have LocationID, but by now I loaded it into memory. Suppose I also have a table of fast food restaurants that has City and State as part of the record. I need to get a list of establishments that match city and state.
NOTE: I try to describe a simplified scenario; my business domain is completely different.
I came up with the following LINQ solution:
var establishments = from r in restaurants
from l in locations
where l.LocationId == id &&
l.City == r.City &&
l.State == r.State
select r
and I feel there must be something better. For starters, I already have City/State in memory - so to go back to the database only to have a join seems very inefficient. I am looking for some way to say {r.City, r.State} match Any(MyList) where MyList is my collection of City/State.
UPDATE
I tried to update based on suggestion below:
List<CityState> myCityStates = ...;
var establishments =
from r in restaurants
join l in myCityStates
on new { r.City, r.State } equals new { l.City, l.State } into gls
select r;
and I got the following compile error:
Error CS1941 The type of one of the expressions in the join clause is incorrect. Type inference failed in the call to 'Join'.
UPDATE 2
Compiler didn't like anonymous class in the join. I made it explicit and it stopped complaining. I'll see if it actually works in the morning...

It seems to me that you need this:
var establishments =
from r in restaurants
join l in locations.Where(x => x.LocationId == id)
on new { r.City, r.State } equals new { l.City, l.State } into gls
select r;

Well, there isn't a lot more that you can do, as long as you rely on a table lookup, the only thing you can do to speed up things is to put an index on City and State.
The linq statement has to translate into a valid SQL Statement, where "Any" would translate to something like :
SELECT * FROM Restaurants where City in ('...all cities')
I dont know if other ORM's give better performance for these types of scenarios that EF, but it might be worth investigating. EF has never had a rumor for being fast on reads.
Edit: You can also do this:
List<string> names = new List { "John", "Max", "Pete" };
bool has = customers.Any(cus => names.Contains(cus.FirstName));
this will produce the necessary IN('value1', 'value2' ...) functionality that you were looking for

How to Get Top 5 Rated User in 2 Tables with LINQ using C#

I have 2 tables, one is Posts another is Comments. These tables contain "RatedPoint" field.
I want to take 5 users who have the highest point.
For example, user ID =1 and its total point 50 in Post table
and it's total point is 25 in Comment table, so its total point is 75
so, i have to look whole members and after choose 5 highest point
It seems a bit complicated, i hope its clear..
I tried something like that
var abc= csEntity.Users.Where(u => csEntity.Posts.Any(p => u.Id == p.UserId)).
Take(userCount).OrderByDescending(u => u.Posts.Count).ToList();
or..
var xyz = csEntity.Posts.Where(p => csEntity.Comments.Any(c => c.UserId == p.UserId));
I dont want to use 2 different list if possible.. is it possible to do it in one query?
I could do it with 2 for loops, but i think its a bad idea..
Post TABLE
Comments TABLE
As you see, these two tables contain userID and each user has RatedPoint...
I think now its clear
EDIT: Maybe a user never write a comment or never write a post just write a comment.. then i think we musnt make equal posts.userId=comments.UserId

Here is a LINQ expression that does what you seem to be asking for:
var result = from p in posts
join c in comments on p.Id equals c.Id
select new { Id = p.Id, Total = p.Points + c.Points };
That provides the actual joined data. Then you can pick the top 5 like this:
result.OrderByDescending(item => item.Total).Take(5)
Note that the above does assume that both tables always have each user, even if they didn't post or comment. I.e. they would simply have a point count of 0. Your updated question clarifies that in your case, you have potentially disjoint tables, i.e. a user can be in one table but not the other.
In that case, the following should work for you:
var leftOuter = from p in posts
join c in comments on p.Id equals c.Id into groupJoin
let c = groupJoin.SingleOrDefault()
select new { Id = p.Id, Total = p.Points + (c == null ? 0 : c.Points) };
var rightAnti = from c in comments
join p in posts on c.Id equals p.Id into groupJoin
let p = groupJoin.SingleOrDefault()
where p == null
select new { Id = c.Id, Total = c.Points };
var result = leftOuter.Concat(rightAnti);
The first LINQ expression does a left outer join. The second LINQ expression does a left anti-join (but I call it "right" because it's effectively the right-join of the original data :) ). I'm using SingleToDefault() to ensure that each user is in each table once at most. The code will throw an exception if it turns out they are present more than once (which otherwise would result in that user being represented in the final result more than once).
I admit, I don't know whether the above is the most efficient approach. I think it should be pretty close, since the joins should be optimized (in objects or SQL) and that's the most expensive part of the whole operation. But I make no promises regarding performance. :)

Linq and RESTful services: how to best merge data from multiple tables in a resultset

I'm experimenting with pulling data from multiple datasets using RESTful services. I'm hooking up to the Cloud version of Northwind, and attempting to use Linq to get the equivalent of this:
SELECT TOP 20 p.ProductName, p.ProductID, s.SupplierID, s.CompanyName AS Supplier,
s.ContactName, s.ContactTitle, s.Phone
FROM Products p
JOIN Suppliers s on p.SupplierID = s.SupplierID
ORDER BY ProductName
So, I define a class to hold my data:
public class ProductSuppliers
{
public string ProductName;
public int ProductID;
public string SupplierName;
public string ContactName;
public string ContactPosition;
public string ContactPhone;
}
And hook into the Northwind service:
NorthwindEntities dc = new NorthwindEntities (new
Uri("http://services.odata.org/Northwind/Northwind.svc/"));
After trying to set up a join, not being able to get it to work, and wandering around in the back corridors of MSDN for a while, I find that Linq joins aren't supported by the OData spec. Which seems obvious once you think about it, given the limitations of URI syntax.
Of course, the usual thing to do is stored procs and views on the server side anyway, handling any sort of joins there. However, I wanted to work out some sort of solution for a situation like this one, where you don't have the capability of creating stored procs or views.
My naive solution has all the elegance of medieval battlefield surgery, and it has to scale horribly. I pulled the two tables as two separate List objects, then iterated one, used Find to locate the matching ID in the other, and Added a combined record into my Product. Here's the code:
public List<ProductSuppliers> GetProductSuppliers()
{
var result = new List<ProductSuppliers>();
ProductSuppliers ps;
var prods =
(
from p in dc.Products
orderby p.ProductName
select p
).ToList();
var sups =
(
from s in dc.Suppliers
select s
).ToList();
foreach (var p in prods)
{
int cIndex = sups.IndexOf(sups.Find(x => x.SupplierID == p.SupplierID));
ps = new ProductSuppliers()
{
ProductName = p.ProductName,
ProductID = p.ProductID,
SupplierName = sups[cIndex].CompanyName,
ContactName = sups[cIndex].ContactName,
ContactPosition = sups[cIndex].ContactTitle,
ContactPhone = sups[cIndex].Phone
};
result.Add(ps);
}
return result;
}
There has to be something better than this, doesn't there? Is there something obvious I'm missing?
[Edit] I've looked at the link someone gave me on the Expand method, and that works...sort of. Here's the code change:
var sups =
(
from s in dc.Suppliers.Expand("Products")
select s
).ToList();
This gives me a list of Suppliers with Products for each in a sublist (dc.Suppliers[0].Products[0], etc.). While I could get what I want from there, I'd still have to iterate the entire list to invert the values (wouldn't I?), so it doesn't look like a more scaleable solution. Also, I can't apply Expand to the Products table to include Suppliers (Changing the from clause in prods to from p in dc.Products.Expand("Suppliers") results in a helpful "An Error occurred while processing this request."). So, it doesn't look like I can expand products to include lookup values from Suppliers, since it looks like expanding is expanding parents to include children, not looking up parent values in a list of children. Is there a way to use Expand (or is there some other mechanism besides client-side manipulation of the two tables) to include lookup values from a foreign key table?

The best you can do is described in this SO answer to a similar question. Not what you expected either, since you're required to make multiple roundtrips to the service.
If you don't control the server-side of things (or you don't want to use SPs/views/joins there) you are forced to use one of these mechanisms.
Anyway, at the very least you can improve the products-suppliers matching in your code to this:
var results = from p in prods
join s in sups on s.SupplierId equals p.SupplierId
select new ProductSuppliers()
{
ProductName = p.ProductName,
ProductID = p.ProductID,
SupplierName = s.CompanyName,
ContactName = s.ContactName,
ContactPosition = s.ContactTitle,
ContactPhone = s.Phone
};
You still need to retrieve all records and join in-memory, though.

Which Linq join will work for my scenario, confused

I have a web api project. In database I have two tables of comments and pictures. I want to use join to merge these two tables in such a way that every picture should have all the comments related to it. Both tables have picture id. Which join should I use? I need to use linq. Can someone tell me the linq query I should use?
I have tried cross join, in this way
var combo = from p in db.picturedetails
from c in db.comments
select new CommentAndPictureDetails
{
IdUser = p.iduser,
IdPictures = p.idpictures,
Likes = p.likes,
NudityLevel = p.nuditylevel,
PicTitle = p.picTitle,
PicTime = p.pictime,
FakesLevel = p.fakeslevel,
Comment1 c.comment1,
CTime = c.ctime,
IdComments = c.idcomments,
SpamLevel = c.spamlevel,
TargetPictureId = c.targetpictureid
};
But I am getting all the pictures with all the comments so a very big json. So which join should i use?

What you're looking for a group join:
var query = from p in db.picturedetails
join c in db.comments
on p.PictureId equals c.PictureId into comments
select new
{
ID = p.PictureId,
Comments = comments,
//...
};

My understanding of LINQ is limited at best but I will try to answer what I assume you are asking.
As far as my understanding of your question goes you are wanting the following to work :
Table1:
PictureID
PictureName
Table2:
PictureID
Comments
And the result to have 1 picture with multiple comments. Is this a correct assumption?
If so I do not believe that is possible with 1 single query as the query will return a picture for every comment, the best way would be to find the 1 picture object, then find the multiple comment objects seperately and return them in some fashion to make it appear as one object.

A C# Linq to Sql query that uses SUM, Case When, Group by, outer join, aggregate and defaults

I've been searching for possible solutions and attempting this for several hours without luck. Any help will be greatly appreciated.
I've got a Sql statement which I'm trying to put together as a C# LINQ query.
Here is the working SQL:
SELECT up.UserProfileID
,up.FirstName
,up.LastName
,SUM(CASE WHEN ul.CompletionDate IS NULL THEN 0
ELSE ISNULL(ul.Score, 0)
END) AS TotalScore
FROM dbo.UserProfile up
LEFT OUTER JOIN dbo.UserLearning ul ON up.UserProfileID = ul.UserProfileID
WHERE up.ManagerUserProfileID IS NULL
GROUP BY up.UserProfileID, up.FirstName, up.LastName
I've tried several different ways but seem to end up with either a statement that doesn't return what I want or doesn't execute successfully
My current (non-working) code looks something like this:
var pd = from up in db.UserProfiles
join ul in db.UserLearnings on up.UserProfileID equals ul.UserProfileID into temp
from upJOINul in temp.DefaultIfEmpty(new UserLearning() { Score = 0 })
where up.ManagerUserProfileID.Equals(null)
group up by new
{
UserProfileID = up.UserProfileID,
FirstName = up.FirstName,
LastName = up.LastName,
TotalScore = up.UserLearnings.Sum(u => u.Score)
};
Thank you for any help

After several more attempts and further use of google I finally managed to get a working solution. I hope it'll be of use to someone else.
var pd = db.UserProfiles.AsEnumerable()
.Where(up => up.ManagerUserProfileID.Equals(null))
.Select(up => new
{
UserProfileID = up.UserProfileID,
FirstName = up.FirstName,
LastName = up.LastName,
TotalScore = up.UserLearnings
.Where(ul => ul.CompletionDate.HasValue && ul.Score.HasValue)
.DefaultIfEmpty()
.Sum(ul => ul != null && ul.Score.HasValue ? ul.Score : 0)
});

Not what you asked for, but if you have a working complex SQL query, that is fairly static, put it in a stored proc, and drag that SP to your LINQ DataContext.
The LINQ provider has to compile your query to sql every time it's called, and that takes time, and server CPU cycles. If it's a complex query, it can eat up significant resources. Also may miss some optimizations you can do with straight SQL.
Unless of course there is a purpose to it.
If you have ORM problem, grap the actual SQL commands, take a look at it, and compare with what you want to achieve. Can you show the generated SQL as well, so we can find the difference easier?