Attempting to display a table with a join on the Rating
to the ID within the Ratings table. I'm hitting an issue with the join within my statement.
var Movie = from u in _context.Movie
join g in _context.Ratings
on u.Rating equals g.ID
select (a => new List
{
Ratings = u.Rating,
MovieRating = g.MovieRating
});
Movie = await Movie.ToListAsync();
The type of one of the expressions in the join clause is incorrect. Type inference failed in the call to 'Join'.
You have some weird syntax like (a => new List { ... Not sure where you are going with that.
Do you have a class named List? are you trying to get a List? Why is "a" in there...since it is not referenced anywhere. You also try to change the type of the Movie variable in your code, the var keyword doesn't work that way. On the first line, you assign a IQueryable< T> to it and later on you try to assign a List< T> to it.
try something like this:
var movieQuery = from u in _context.Movie
join g in _context.Ratings on u.Rating equals g.ID
select new
{
Ratings = u.Rating,
MovieRating = g.MovieRating
};
var movies = await movieQuery.ToListAsync(); // query will be executed here
The example code above uses an anonymous class as result so movies will be of type List< T> where T is an anonymous class, if you do have a class called List (for some reason) representing a single result item, then use
select new List { ...
instead of
select new { ...
and if you don't wanna split the query / actual list into 2 variables, you can do something like:
var movies = await (from u in _context.Movie
join g in _context.Ratings on u.Rating equals g.ID
select new
{
Ratings = u.Rating,
MovieRating = g.MovieRating
}).ToListAsync();
Related
I'm doing a query which gets back the names of the buyers grouped by the brand of the products they have bought. So far I'm here
var query= from p in purchaseRepo.ReadAll()
join g in guitarRepo.ReadAll() on p.GuitarId equals g.Id
join b in brandRepo.ReadAll() on g.BrandId equals b.Id
group p by b.Id into grp
select new
{
grp.Key,
grp.SelectMany(t => t.BuyerName)
}
My problem is that I would like to have a List or an array of the buyer names declared in the select new part's body, but I can't get it to work.
EDIT:
I've given names for the fields is select new it looks like this:
select new
{
Brand=grp.Key,
Buyers=new List<string>()
};
Now I only need to know how to get the buyer names into the List.
The result should be something like this:
Brand1 --->List of buyer names
Pick one:
Linq offers the .ToList() method
Linq offers the .ToArray() method
Be a hero and implement your own method that accepts an IEnumerable<string> and returns a list populated with the string elements from that enumerable...
I've managed to get it working, thanks everyone for the help!
Here's my query for others struggling:
var asd = from p in purchaseRepo.ReadAll()
join g in guitarRepo.ReadAll() on p.GuitarId equals g.Id
join b in brandRepo.ReadAll() on g.BrandId equals b.Id
group p by b.Name into grp
select new
{
Brand = grp.Key,
Buyers = grp.Select(t=>t.BuyerName)
};
var result = asd
.Select(x => new KeyValuePair<string, List<string>>(
x.Brand,
x.Buyers.ToList()
));
Context
I am trying to get a list from select new:
var portfolioresult =
(from port in _context.Portfolio
join u in _context.Universe on port.CUSIP equals u.ID_CUSIP
join m in _context.MarketDataEvent on u.ID_CUSIP equals m.CUSIP_NUMBER_REALTIME
//select new { m, port.Name }).ToList();
select new ViewResult() { MarketDataEvents = m, PortfolioName = port.Name })
.ToList();
I want to get MarketDataEvents as List<MarketDataEvent>
Corresponding SQL query
SELECT me.*, p.Name FROM MarketDataEvent me
INNER JOIN universe u ON u.ID_CUSIP=me.CUSIP_NUMBER_REALTIME
INNER JOIN portfolio p ON p.CUSIp=me.CUSIP_NUMBER_REALTIME
Problem
I am not able to get a List inside select new. Is it possible to get something like this?
select new ViewResult() { MarketDataEvents = List<MarketDataEvents>, PortfolioName = port.Name })
Expected result
List<MarketDataEvents> "XYZ"
List<MarketDataEvents> "ABC"
Actual result
MarketDataEvent "XYZ
MarketDataEvent "XYZ"
MarketDataEvent "ABC"
Yes, it is possible:
var query =
from port in _context.Portfolio
select new ViewResult
{
MarketDataEvents =
(from u in _context.Universe.Where(u => port.CUSIP == u.ID_CUSIP)
join m in _context.MarketDataEvent on u.ID_CUSIP equals m.CUSIP_NUMBER_REALTIME
select m).ToList(),
PortfolioName = port.Name
};
var portfolioresult = query.ToList();
Essentially your m reference is out of scope. The input available to a select statement is only a single value out of the set available as a result of the select/joins you're looking at, which is why you don't see a list of all available from m, only a single value in each record.
Rather, you need to use a SelectMany since it'll expose an IEnumerable as the input to the function and you can split out the individual XYZ values out of that.
I want to join 2 tables using linq and avoid anonymous object.
So far i use tuple.
var products = from tm in db.TargetMarkets
join tp in db.Products on tm.product_id equals tp.id
where tm.country == 2
select Tuple.Create<TargetMarket, Product>(tm, tp);
But, when i foreach
foreach (var p in products)
{
var a = p.Item1.id;
}
It throws an exception
LINQ to Entities does not recognize the method 'System.Tuple`2
Question:
Is there a way to keep my code strongly typed
What's wrong with tuple (optional)
Is there a way to keep my code strong type
You can define a new type and make object of that type instead of anonymous object.
class ProductTargetMarket
{
//Attributes
}
var ProductsTargetMarkets = from tm in db.TargetMarkets
join tp in db.Products on tm.product_id equals tp.id
where tm.country == 2
select new ProductTargetMarket{Attribute1OfProductTargetMarket = tp.Attribute1, Attribute1OfProductTargetMarket = tm.Attribute1 };
To create a tuple you may first convert it to anonymous type and then convert it to tuple, see this this and this post.
I am pretty new to Entity Framework and LINQ and I have an entity with more than 10+ other associated entities (one-to-many relationships). Now, I'm planning to make a search page in my application in which users could select which fields (i.e. those 10+ tables) they want to be considered when searching.
Now, I'm trying to write a query to achieve the above goal. Any help how I could sort this out using LINQ method syntax? I mean, to write a multiple join query based on user's choice. (i.e. which of Class1, Class2, ... to join with main Entity to finally have all the related fields in one place). Below is a sample code (Just a hunch, in fact)
if(somefilter#1)
result = db.Companies.Join(db.Channels, p => p.Id, k => k.CId,
(p, k) => new {Company = p, Channels=k});
if(somefilter#2)
result = result.Join(db.BusinnessType, ........);
if(somefilter#3)
result = result.Join(db.Values, .......);
For complex queries it may be easier to use the other LINQ notation. You could join multiple entities like this:
from myEntity in dbContext.MyEntities
join myOtherEntity in dbContext.MyOtherEntities on myEntity.Id equals myOtherEntity.MyEntityId
join oneMoreEntity in dbContext.OneMoreEntities on myEntity.Id equals oneMoreEntity.MyEntityId
select new {
myEntity.Id,
myEntity.Name,
myOtherEntity.OtherProperty,
oneMoreEntity.OneMoreProperty
}
You can join in other entities by adding more join statements.
You can select properties of any entity from your query. The example I provided uses a dynamic class, but you can also define a class (like MyJoinedEntity) into which you can select instead. To do it you would use something like:
...
select new MyJoinedEntity {
Id = myEntity.Id,
Name = myEntity.Name,
OtherProperty = myOtherEntity.OtherProperty,
OneMoreProperty = oneMoreEntity.OneMoreProperty
}
EDIT:
In case when you want to have conditional joins you can define MyJoinedEntity with all the properties you will need if you were to join everything. Then break up the join into multiple methods. Like this:
public IEnumerable<MyJoinedEntity> GetEntities() {
var joinedEntities = from myEntity in dbContext.MyEntities
join myOtherEntity in dbContext.MyOtherEntities on myEntity.Id equals myOtherEntity.MyEntityId
join oneMoreEntity in dbContext.OneMoreEntities on myEntity.Id equals oneMoreEntity.MyEntityId
select new MyJoinedEntity {
Id = myEntity.Id,
Name = myEntity.Name,
OtherProperty = myOtherEntity.OtherProperty,
OneMoreProperty = oneMoreEntity.OneMoreProperty
};
if (condition1) {
joinedEntities = JoinWithRelated(joinedEntities);
}
}
public IEnumerable<MyJoinedEntity> JoinWithRelated(IEnumerable<MyJoinedEntity> joinedEntities) {
return from joinedEntity in joinedEntities
join relatedEntity in dbContext.RelatedEntities on joinedEntity.Id equals relatedEntity.MyEntityId
select new MyJoinedEntity(joinedEntity) {
Comments = relatedEntity.Comments
};
}
I have 2 tables in a database, and one class in C# (Letter).
Tables: tblUser(Id, Name), tblLetter(Id, UserId, Title)
Letter: (Id, Title, UserName)
I want select data with linq, and use this code:
List<Letter> lst = new List<Letter>();
lst = (from l in l.tblLetter.ToList()
select new {l.Id, l.Title, UserName = l.tblUser.Name}
).ToList();
and:
List<Letter> lst = new List<Letter>
(from l in l.tblLetter.ToList()
select new {l.Id, l.Title, UserName = l.tblUser.Name});
but get this error:
Cannot implicitly convert type...
As #SnowYetis comments, you are actually selecting an instance of a new, anonymous type in your code. That's what the syntax new { ... } does. Notice that there's no type name after the new directive.
If your Letter type has the properties Id, Title, UserName then all you need to do is change new { ... } to new Letter { ... }.
If not, then we probably need more information than you're giving us—for example, the definition of the Letter type.
There are a few issues in your code:
l.tblLetter.ToList() returns all records from your table. You typically don't call ToList() until the end of your query, to get just the data you need and no more.
You want to do a join between the two tables to get the matching user name.
If you want to return a collection of Letter, you can create instances of that in your select statement instead of creating an anonymous type.
Try this:
var lst = (from l in l.tblLetter
join u in tblUser on l.UserId equals u.Id
select new Letter
{
Id = l.Id,
Title = l.Title,
UserName = u.Name
}).ToList();