i've got a List of objects, lets call them Product, which each of them contains a bunch of properties and also a List of Version (which are also objects).
Version also has a bunch of properties and does contain a List of Customer (which again are objects).
Customer again has properties, one of them is its ID (=Guid).
What i try to do is to make a List of Product, selected by a certain ID of its Product.VersionList.Version.ID.
I would prefere a join query, but every efficient way is welcome. I tried so far this, but because i have only a single ID to compare with, i don't know how to construct the join.
lp = List<Entity.Product>;
g = GetGuid();
var query = from product in Entity.ProductCollection
join g in g
on product.Version.Where(x => x.id == g)
select product;
lp.AddRange(query);
I'm guessing you mean:
var query = from product in Entity.ProductCollection
where product.Version.Any(x => x.id == g)
select product;
i.e. select all the products that have a version where the id matches the guid you were thinking of.
Note that joining to the versions would cause product duplication if any product has multiple matching versions.
Try this .... May be you wants more deep digging on it..
var query = from Product product in pc
from varsion in product.Version
let v= varsion as Entity.Version
where v.id == g
select product;
var query = Entity.ProductCollection.Where(p => p.Version.Any(v => v.Id == g));
You can use Any rather than having to do a self join.
Related
I have a database that contains 3 tables:
Phones
PhoneListings
PhoneConditions
PhoneListings has a FK from the Phones table(PhoneID), and a FK from the Phone Conditions table(conditionID)
I am working on a function that adds a Phone Listing to the user's cart, and returns all of the necessary information for the user. The phone make and model are contained in the PHONES table, and the details about the Condition are contained in the PhoneConditions table.
Currently I am using 3 queries to obtain all the neccesary information. Is there a way to combine all of this into one query?
public ActionResult phoneAdd(int listingID, int qty)
{
ShoppingBasket myBasket = new ShoppingBasket();
string BasketID = myBasket.GetBasketID(this.HttpContext);
var PhoneListingQuery = (from x in myDB.phoneListings
where x.phonelistingID == listingID
select x).Single();
var PhoneCondition = myDB.phoneConditions
.Where(x => x.conditionID == PhoneListingQuery.phonelistingID).Single();
var PhoneDataQuery = (from ph in myDB.Phones
where ph.PhoneID == PhoneListingQuery.phonePageID
select ph).SingleOrDefault();
}
You could project the result into an anonymous class, or a Tuple, or even a custom shaped entity in a single line, however the overall database performance might not be any better:
var phoneObjects = myDB.phoneListings
.Where(pl => pl.phonelistingID == listingID)
.Select(pl => new
{
PhoneListingQuery = pl,
PhoneCondition = myDB.phoneConditions
.Single(pc => pc.conditionID == pl.phonelistingID),
PhoneDataQuery = myDB.Phones
.SingleOrDefault(ph => ph.PhoneID == pl.phonePageID)
})
.Single();
// Access phoneObjects.PhoneListingQuery / PhoneCondition / PhoneDataQuery as needed
There are also slightly more compact overloads of the LINQ Single and SingleOrDefault extensions which take a predicate as a parameter, which will help reduce the code slightly.
Edit
As an alternative to multiple retrievals from the ORM DbContext, or doing explicit manual Joins, if you set up navigation relationships between entities in your model via the navigable join keys (usually the Foreign Keys in the underlying tables), you can specify the depth of fetch with an eager load, using Include:
var phoneListingWithAssociations = myDB.phoneListings
.Include(pl => pl.PhoneConditions)
.Include(pl => pl.Phones)
.Single(pl => pl.phonelistingID == listingID);
Which will return the entity graph in phoneListingWithAssociations
(Assuming foreign keys PhoneListing.phonePageID => Phones.phoneId and
PhoneCondition.conditionID => PhoneListing.phonelistingID)
You should be able to pull it all in one query with join, I think.
But as pointed out you might not achieve alot of speed from this, as you are just picking the first match and then moving on, not really doing any inner comparisons.
If you know there exist atleast one data point in each table then you might aswell pull all at the same time. if not then waiting with the "sub queries" is nice as done by StuartLC.
var Phone = (from a in myDB.phoneListings
join b in myDB.phoneConditions on a.phonelistingID equals b.conditionID
join c in ph in myDB.Phones on a.phonePageID equals c.PhoneID
where
a.phonelistingID == listingID
select new {
Listing = a,
Condition = b,
Data = c
}).FirstOrDefault();
FirstOrDefault because single throws error if there exists more than one element.
I have two database tables Contact (Id, Name, ...) and ContactOperationalPlaces (ContactId, MunicipalityId), where a contact can be connected to several ContactOperationalPlaces.
What I'm trying to do is to build a query (ASP .NET, C#) with IQueryable, that only selects all the contacts that exists in the ContactOperationalPlaces table, with a given MunicipalityId.
The sql query looks like this:
select * from Contacts c
right join ContactOperationPlaces cop on c.Id = cop.ContactId
where cop.MunicipalityId = 301;
With linq it would look something like this:
//_ctx is the context
var tmp = (from c in _ctx.Contacts
join cop in _ctx.ContactOperationPlaces on c.Id equals cop.ContactId
where cop.MunicipalityId == 301
select c);
So, I know how to do this if the point was to select all of this at once, unfortunately it's not. I'm building a query based on user input, so I don't know all of the selection at once.
So this is what my code looks like:
IQueryable<Contacts> query = (from c in _ctx.Contacts select c);
//Some other logic....
/*Gets a partial name (string nameStr), and filters the contacts
so that only those with a match on names are selected*/
query = query.Where(c => c.Name.Contains(nameStr);
//Some more logic
//Gets the municipalityId and wants to filter on it! :( how to?
query = query.where(c => c.ContactOperationalPlaces ...........?);
The difference with the two where statements is that with the first one, each contact has only one name, but with the latter a contact can contain several operational places...
I have managed to find one solution, but this solution gives me an unidentyfied object, that contains both of the tables. And I don't know how to proceed with it.
query.Join(_ctx.ContactOperationPlaces, c => c.Id, cop => cop.ContactId,
(c, cop) => new {c, cop}).Where(o => o.cop.municipalityId == 301);
The object returned from this expression is System.Linq.Iqueryable<{c:Contact, cop:ContactOperationalPlace}>, and it can't be cast to Contacts...
So, that's the issue. The answer is probably pretty simple, but I just can't find it...
You create an anonymous type with both objects before your where clause and filter it on ContactOperationPlaces value. You just have to select the Contact after that.
query.Join(_ctx.ContactOperationPlaces, c => c.Id, cop => cop.ContactId,
(c, cop) => new {c, cop}).Where(o => o.cop.municipalityId == 301)
.Select(o => o.c)
.Distinct();
You don't need to return new objects in the result selector function. The delegate provides both variables so you can choose one or the other, or some other variation (which would require a new object). Try this:
query.Join(_ctx.ContactOperationPlaces, c => c.Id, cop => cop.ContactId,
(c, cop) => c).Where(o => o.cop.municipalityId == 301);
can you just cast it to var and try to use intellisense on it?
var myCast = query.Join(_ctx.ContactOperationPlaces, c => c.Id, cop => cop.ContactId,
(c, cop) => new {c, cop}).Where(o => o.cop.municipalityId == 301);
Just a thought
I think it would be much easier if you start this as 2 different queries, then combine them. I'm assuming the relation is Contact (1 <-> many) Contactoperationplaces ? And in the end, you will be showing 1 item per Contactoperationplaces, not 1 item per Contact?
Do it like this:
IQueryable<Contacts> query = (from c in _ctx.Contacts select c);
...
query = query.Where(x=> x.Name.ToLower().Contains(nameStr.ToLower());
...
IQueryable<ContactOperationPlaces> query_2 =
(from c in _ctx.ContactOperationPlaces
where query.Where(x=> x.Name == c.Contact.Name).Count() > 0
select c);
//Now query_2 contains all contactoperationsplaces which have a contact that was found in var query
Conversely, there is a much easier way to do this, and that's by skipping the first part entirely.
IQueryable<ContactOperationPlaces> query_2 =
(from c in _ctx.ContactOperationPlaces
where c.Contact.Name.ToLower().Contains(strName.ToLower())
select c);
If you're using Entity Framework, you don't have to do any joins as long as you defined associations between the tables.
Now that I look at it, my second solution is far more efficient and easier. But if you need to do some other processing inbetween these commands, solution one works too :)
If you need more explanation, feel free to ask :)
I currently a list of a Supplier class, within that supplier class is a list of orders.
Each order has a userID and an empty string variable for username.
I then have a list of users which contains userID and username.
The way I am doing this now is:
foreach(supplier s in SupplierList)
{
foreach (order o in s.childorders)
{
user u = _users.First(p => p.userid == o.userid);
o.username = u.username;
}
}
I feel this might be a little inefficient and I was wondering if it is possible to compact it down into one linq query?
The logic should be
set supplierslist.childorders.username to the value in _users where supplierslist.childorders.userid == _users.userid.
Im fairly new to Linq so any advice for this would be apreciated, or also if its a bad idea and to leave it as it is / reasons why would be good too.
Thanks
What you want to do here is iterate over a collection (many collections, really, but it doesn't make a difference) and mutate its members. LINQ is not really targeted at performing mutating operations but rather at querying. You can do it with LINQ, but it's against the spirit of the tool.
If you are constructing the SupplierList yourself, it might be possible to fetch the data appropriately with LINQ so that it comes pre-populated as you want it to be.
Otherwise, I 'd leave the foreach as it is. You can make a dictionary that maps ids to users to make the inner loop faster, but that's your call and it depends on your data size.
var orderUserPairs = SupplierList
.SelectMany(s => s.ChildOrders)
.Join(_users, o => o.UserId, u => u.userId, (Order, User) => new {Order, User});
foreach (var orderUserPair in orderUserPairs)
orderUserPair.Order.username = orderUserPair.User.username;
Though having both username and userId as part of order looks suspicious.
First a question...
It looks like you are operating on every order. Why do you need to cycle through the supplierlist first since you don't seem to be using it inside the loop? Unless there are orders that don't belong to any supplierlist, you might be able to skip that step.
If that isn't the case, then I think you can use a join. If you aren't familiar with the syntax for joins in linq, this is one (simplified) way to approach it:
var x = from S in SupplierList
join C in childorders on C.supplierlistID equals S.ID
where [whatever you need here if anything]
select new { field1, field2};
foreach var y in x
{
}
Note I assumed a foreign key in childorders to supplierlist. If that isn't the case you will have to modify accordingly.
Hope that helps.
You need to use SelectMany or join depending on weather you are using linq-to-sql or linq with local collections. If you are using local collections the better way is to use join, else use SelectMany.
Like this...join:
var selection = (from s in SupplierList
join o in s.childholders on s.userid equals o.userid
select new { username = o.username);
or, in case of linq-to-sql:
var selection = (from s in SupplierList
from o in s.childholders
select { username = o.username);
You can then use the anonymous type you projected the way you want.
I agree with Jon, but you could say:
var orders = (from s in supplier
from o in s.childorders
select new
{
Order = o,
User = _users.First(p => p.userid == o.userid)
}).ToList();
foreach(var order in orders) {
order.Order.username = order.User.username;
}
Untested of course :)
If users list contains many elements, it can be really slow so I'd use a temporary dictionary:
var userById = users.GroupBy(x => x.userid)
.ToDictionary(x => x.Key, x => x.First());
foreach(var order in supplier.SelectMany(x => x.childorders))
{
order.username = userById[order.userid].username;
}
I would like to get the list of albums (Distinct) which was sung by the artistId=1
I am very new to LINQ to SQL and do not know how to join multiple tables. Please see the database diagram below:
alt text http://a.imageshack.us/img155/8572/13690801.jpg
SingBy is the middle table between Track and Artist.
How could I achieve this?
var albums = from singer in artist
from sb in singby
from t in track
from a in album
where singer.artistId == 1 &&
sb.artistId == 1 &&
sb.trackId == t.trackId &&
a.albumId == track.albumId
select a;
I'm sure there must be a better way. You should look into creating Navigation Properties on your entities. Navigation Properties are like foreign keys.
Edit - corrected to get albums, not artists.
Now, I wrote the codes like the following and it works.
var albums = (from a in db.artists
where a.artistId == 1
join sb in db.singbies on a equals sb.artist
join t in db.tracks on sb.track equals t
join al in db.albums on t.album equals al
select al).Distinct();
return albums.ToList() as List<album>;
I tested the Chad's version and it works too. I would like to know which way is better and good for query optimization? Thanks all.
If you have all the foreign key relationship defined, you should be able to issue call like below:
dc.GetTable<Album>().Where(a => a.Track.Singby.ArtistId == 1).ToList();
This is relying on Linq to perform lazy load for Track and Singby automatically when required. Obviously this is not optimal to use when you have a large set of data in the db and performance is critical. You can chain the query with GroupBy or Distinct operation to return only the distinct set such as
dc.GetTable<Album>().Where(a => a.Track.Singby.ArtistId == 1).Distinct().ToList();
I would like to get the list of albums
(Distinct) which was sung by the
artistId=1
DBDataContext = new DBDataContext();
album[] = db.artists.Where(a => a.artistId == 1) /* Your artist */
.SelectMany(a => a.singbies) /* Check if `singby` converted to `singbies` */
.Select(sb => sb.track) /* The tracks */
.Select(t => t.album) /* The albums */
.GroupBy(al => al.albumId) /* Group by id */ /* "Distinct" for objects */
.Select(alG => alG.First()) /* Select first of each group */
.ToArray();
IEnumerable<Album> query =
from album in myDC.Albums
let artists =
from track in album.Tracks
from singBy in track.SingBys
select singBy.Artist
where artists.Any(artist => artist.ArtistId == 1)
select album;
List<int> Ids = dc.Albums.Where(a => a.Track.Singby.ArtistId == 1).Select(a=> a.albumId).Distinct().ToList();
List<Album> distinctAlbums = dc.Albums.Where(a => distinctAlbumIds.Contains(a.albumId)).ToList();
Hey TTCG, above is the simplest way to do it. This is because doing a Distinct on a List of objects won't do it based on the albumId.
Either you do it in two steps as above, or, you write your own Album Comparer which specifies uniqueness based on AlbumId and pass it to the Distinct call on a List.
NOTE:
The above will only work if you've defined the constraints in your DBML, but better still in your DB.
For best practices, always define your relationships IN THE DATABASE when using Linq to SQL, as Linq to SQL is not like EF, or NHibernate, in that is does not "abstract" your db, it simply reflects it. It's a tool for Data Driven Design, not Domain Driven, so define the relationships in the db.
table data of 2 columns "category" and "subcategory"
i want to get a collection of "category", [subcategories]
using code below i get duplicates. Puting .Distinct() after outer "from" does not help much. What do i miss?
var rootcategories = (from p in sr.products
orderby p.category
select new
{
category = p.category,
subcategories = (
from p2 in sr.products
where p2.category == p.category
select p2.subcategory).Distinct()
}).Distinct();
sr.products looks like this
category subcategory
----------------------
cat1 subcat1
cat1 subcat2
cat2 subcat3
cat2 subcat3
what i get in results is
cat1, [subcat1,subcat2]
cat1, [subcat1,subcat2]
but i only want one entry
solved my problem with this code:
var rootcategories2 = (from p in sr.products
group p.subcategory by p.category into subcats
select subcats);
now maybe it is time to think of what was the right question.. (-:
solved with this code
var rootcategories2 = (from p in sr.products
group p.subcategory by p.category into subcats
select subcats);
thanks everyone
I think you need 2 "Distinct()" calls, one for the main categories and another for the subcategories.
This should work for you:
var mainCategories = (from p in products select p.category).Distinct();
var rootCategories =
from c in mainCategories
select new {
category = c,
subcategories = (from p in products
where p.category == c
select p.subcategory).Distinct()
};
The algorithm behind Distinct() needs a way to tell if 2 objects in the source IEnumerable are equal.
The default method for that is to compare 2 objects by their reference and therefore its likely that no 2 objects are "equal" since you are creating them with the "new" keyword.
What you have to do is to write a custom class which implements IEnumerable and pass that to the Distinct() call.
Your main query is on Products, so you're going to get records for each product. Switch it around so you're querying on Category, but filtering on Product.Category