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SQL to LINQ expres

I'm trying to convert a SQL expression to Linq but I can't make it work, does anyone help?
SELECT
COUNT(descricaoFamiliaNovo) as quantidades
FROM VeiculoComSeminovo
group by descricaoFamiliaNovo
I try this:
ViewBag.familiasCount = db.VeiculoComSeminovo.GroupBy(a => a.descricaoFamiliaNovo).Count();
I need to know how many times each value repeats, but this way it shows me how many distinct values ​​there are in the column.

You can try:
var list = from a in db.VeiculoComSeminovo
group a by a.descricaoFamiliaNovo into g
select new ViewBag{
familiasCount=g.Count()
};
or
var list = db.VeiculoComSeminovo.GroupBy(a => a.descricaoFamiliaNovo)
.Select (g => new ViewBag
{
familiasCount=g.Count()
});
If you need column value:
new ViewBag{
FieldName=g.Key,
familiasCount=g.Count()
};

You don't need the GROUP BY unless there are fields other than the one in COUNT. Try
SELECT
COUNT(descricaoFamiliaNovo) as quantidades
FROM VeiculoComSeminovo
UPDATE, from your comment:
SELECT
COUNT(descricaoFamiliaNovo) as quantidades,
descricaoFamiliaNovo
FROM VeiculoComSeminovo
GROUP BY descricaoFamiliaNovo
That's it as SQL. In LINQ it is something like:
var reponse = db.VeiculoComSeminovo.GroupBy(a => a.descricaoFamiliaNovo)
.Select ( n => new
{Name = n.key,
Count = n.Count()
}
)
Not tested.

Ty all for the help.
I solved the problem using this lines:
// get the objects on db
var list = db.VeiculoComSeminovo.ToList();
// lists to recive data
List<int> totaisFamilia = new List<int>();
List<int> totaisFamiliaComSN = new List<int>();
// loop to cycle through objects and add the values ​​I need to their lists
foreach (var item in ViewBag.familias)
{
totaisFamilia.Add(list.Count(a => a.descricaoFamiliaNovo == item && a.valorSeminovo == null));
totaisFamiliaComSN.Add(list.Count(a => a.descricaoFamiliaNovo == item && a.valorSeminovo != null));
}
The query was a little slow than I expected, but I got the data

LINQ Select Last & Unique Record from a DB using List

I have a table where all vehicles are registered and another table where I have millions of pings for each registered vehicle.
I'm trying to select the last ping from each vehicle that has sent a ping in the last 30 minutes using the LINQ QUERY. I've done the code below through the "for each" idea, but I'm not sure if it is the best way to do.
I would like to know if there is any better way to select this using a single line? I know that I can "group by" them by vehicle_fleetNumber but I couldn't achieve the proper result as the TAKE() is limiting the final result.
var timeRestriction = DateTime.UtcNow.AddMinutes(-30);
var x = _db.Vehicles.Where(r=> r.isActive.Equals(true) && r.helperLastPing > timeRestriction);
foreach (var vehicle in x)
{
var firstOrDefault = _db.Tracks.OrderByDescending(r => r.collectedOn)
.FirstOrDefault(r => r.vehicle_fleetNumber.Equals(vehicle.fleetNumber));
}
return View();
Thank you,

Yes, you should do it in the database by joining both tables and using GroupBy:
var query = from v in _db.Vehicles
join t in _db.Tracks
on v.fleetNumber equals t.vehicle_fleetNumber
where v.isActive && v.helperLastPing > timeRestriction
group t by t.vehicle_fleetNumber into vehicleGroup
select vehicleGroup.OrderByDescending(x => x.collectedOn).First();
foreach(var track in query)
{
// ...
}
Instead of the foreach you can also use query.ToArray or ToList, i don't know what you want to do with it.

If you get moreLinq from nuget you will find the .maxby() method:
for example in a different context:
//get the correct exchange rate
var rateList = _db.lists_ExchangeRates.Where(
rates => rates.Currency == currencyCode);
Decimal? exRate = rateList.MaxBy(rates => rates.LastUpdated).ExchangeRate;
Also see below this gives additional info.
MoreLinq maxBy vs LINQ max + where

In my case if I want the last data that has been save I use this method
var id = db.DPSlips.Max(item => item.Id);
So I thought this might work as will just try
var timeRestriction = DateTime.UtcNow.AddMinutes(-30);
var x = _db.Vehicles.Max(a => a.isActive == true && a.helperLastPing > timeRestriction);

C# List grouping and assigning a value

I have a list of Orders. This list contains multiple orders for the same item, see the table below.
I then want to assign each item that is the same (i.e. ABC) the same block ID. So ABC would have a block ID of 1 & each GHJ would have a block ID of 2 etc. What is the best way of doing this?
Currently I order the list by Order ID and then have a for loop and check if the current Order ID is equal to the next Order ID if so assign the two the same block ID. Is there a better way of doing this using linq or any other approach?
Order ID Block ID
ABC
ABC
ABC
GHJ
GHJ
GHJ
MNO
MNO

You can do this that way, it will assign same blockid for same orderid
var ordered = listOrder.GroupBy(x => x.OrderId).ToList();
for (int i = 0; i < ordered.Count(); i++)
{
ordered[i].ForEach(x=>x.BlockId=i+1);
}
it will group orders by orderid then assign each group next blockid. Note that it won't be done fully in linq, because linq is for querying not changing data.

Always depends of what better means for you in this context.
There are a bunch of possible solutions to this trivial problem.
On top of my head, I could think of:
var blockId = 1;
foreach(var grp in yourOrders.GroupBy(o => o.OrderId))
{
foreach(var order in grp)
{
order.BlockId = blockId;
}
blockId++;
}
or (be more "linqy"):
foreach(var t in yourOrders.GroupBy(o => o.OrderId).Zip(Enumerable.Range(1, Int32.MaxValue), (grp, bid) => new {grp, bid}))
{
foreach(var order in t.grp)
{
order.BlockId = t.bid;
}
}
or (can you still follow the code?):
var orders = yourOrders.GroupBy(o => o.OrderId)
.Zip(Enumerable.Range(1, Int16.MaxValue), (grp, id) => new {orders = grp, id})
.SelectMany(grp => grp.orders, (grp, order) => new {order, grp.id});
foreach(var item in orders)
{
item.order.BlockId = item.id;
}
or (probably the closest to a simple for loop):
Order prev = null;
blockId = 1;
foreach (var order in yourOrders.OrderBy(o => o.OrderId))
{
order.BlockId = (prev == null || prev.OrderId == order.OrderId) ?
blockId :
++blockId;
prev = order;
}
Linq? Yes.
Better than a simple loop? Uhmmmm....
Using Linq will not magically make your code better. Surely, it can make it often more declarative/readable/faster (in terms of lazy evaluation), but sure enough you can make otherwise fine imperative loops unreadable if you try to force the use of Linq just because Linq.
As a side note:
if you want to have feedback on working code, you can ask at codereview.stackexchange.com

using linq to order tickets by lowest date where ticket is not closed?

I have an object called Ticket with that contains a list of objects called TicketActions. The Ticket object has a field called Date_Closed and the Actions object has a field called Action_Date:
Ticket
Date_Closed
TicketActions
-Action_Date
What I'm trying to do is order a List of tickets (List) based on the latest date of each Action in ascending order where the Ticket does not have a value for Date_Closed. The goal is to load this list into a listview and show tickets in a way that displays tickets in order on the page, placing the ones that have gone the longest without an action at the top. Does that make sense?
Here is what I ended up with so far that isn't working:
protected List<FullTicket> BuildTickets(int ticketsToShow)
{
using (var db = new SupportLogDBDataContext())
{
var result =
(from ticket in db.Support_Tickets
join status in db.Ticket_Statuses on ticket.Status_ID equals status.ID
select new FullTicket
{
TicketID = ticket.ID,
DateOpened = (DateTime)ticket.Date_Opened,
DateClosed = (DateTime)ticket.Date_Closed,
Subject = ticket.Subject,
Status = new KeyPair { Key = status.Status, Value = status.ID },
CreatedBy = new GuidPair { Key = ticket.Reported_By, Value = (Guid)ticket.AD_GUID },
TicketActions =
(from a in db.Ticket_Actions
where a.Ticket_ID == ticket.ID
select a).ToList()
}).Take(ticketsToShow).ToList();
result.OrderBy(i => i.TicketActions.Where(i.DateClosed == null).Max()); //error on this line (invalid arguments)
return result;
}
}

People reply quick here!
Try this:
var result = (from ticket in tickets
where !ticket.DateClosed.HasValue
select ticket).OrderByDescending(t => (from a in t.TicketActions
select a.ActionDate).Max());
From here you can take as many as you need.

David B's analysis is slightly off. The line...
result.OrderBy(i => i.TicketActions.Where(i.DateClosed == null).Max());
... will not compile because the argument to the Where method is not a lambda expression or delegate.
I would suggest this solution (assuming that the relevant property of the TicketAction type is ActionDate):
return result.Where(i => i.DateClosed == null)
.OrderBy(i => i.TicketActions.Max(a => a.ActionDate));
Or, in query comprehension syntax:
return from i in result
where i.DateClosed == null
orderby i.TicketActions.Max(a => a.ActionDate)
select i;

Here is some simple code.
var sorted = tickets.Where(t => t.DateClosed == null)
.OrderBy(t => t.TicketActions.Max(ta => ta.Action_Date.Ticks));
Sorry, I prefer LINQ function syntax, but if you want it in query syntax, it shouldn't be too hard to convert.

result.OrderBy(i => i.TicketActions.Where(i.DateClosed == null).Max());
This line generates an error because TicketActions.Max() is not defined.
You need to project TicketAction into something that can be Max'd. For example:
result.OrderBy(i =>
i.TicketActions
.Where(ta => i.DateClosed == null)
.Select(ta => ta.Id)
.Max()
);
Also note:
OrderBy does not modify its source. OrderBy returns an ordered IEnumerable, which you didn't assign anywhere.
OrderBy's enumerable is deferred, and you want a List result instead, so you should call ToList.
You are accessing Ticket.TicketActions outside of the query. This will cause one database round trip per ticket to load that property.
Here is a modification to your query that avoids the problems mentioned above by ordering and using navigational properties within the query.
from ticket in db.Support_Tickets
where ticket.DateClosed == null
let lastDate = ticket.TicketActions
.Select(ta => ta.ActionDate)
.OrderByDescending(date => date)
.FirstOrDefault()
let ticketStatus = ticket.TicketStatus
order by lastDate
select new FullTicket
{
...
}

Method x has no supported translation to SQL

I want to write a query which should get an user object and the amount of messages the user has posted already. I did this the following way:
var query = (from u in _db.Repository<User>()
where u.IsDeleted != true
select new UserWithMessagecount()
{
User = u
MessageCount = GetUserMessageCount(u.Documents).Count(),
});
I'm using a method because some messages should be filtered out (in a dynamic way).
To keep things simple I'll post the function without sorting logic (which still produces the same error).
private EntitySet<Document> GetUserMessageCount(EntitySet<Document> set)
{
return set;
}
The error returned is:
Method 'x' has no supported translation to SQL.
Any ideas on how to fix this issue?

use this syntax instead:
var query = (from u in _db.Repository<User>()
let MessageCount = GetUserMessageCount(u.Documents).Count()
where u.IsDeleted != true
select new UserWithMessagecount()
{
User = u,
MessageCount = MessageCount
});

Linq-to-SQL will be trying to convert your entire statment into SQL, an of course there is no GetUserMessageCount() available.
You will need to take the results of the SQL query by enumerating it -- then apply the C# side logic.

What you need to do is to use grouping in your projection.
var query = from u in _db.Repository<User>()
where !u.IsDeleted
group u by u.UserId into g
select new UserWithMessageCount {
User = g.First(x => x.UserId == g.Key),
MessageCount = g.Sum(x => x.Messages.Count())
}
This should work.