Develop Reference

Incrementing an ID using LINQ

Whenever I'm adding a new object from the front end, the id = 0. In the WebApi layer, I'm trying to find the max ID that exists in the list of object and then assign the next ID to the new objects. The code below doesn't increment the ID correctly
List<Event> events = eventVal.Where(e => e != null).ToList();
int eventMaxID = events.Max(e => e.id);
events.Where(e => e.id == 0)
.Select((e, ixc) => new { id = eventMaxID + 1, Iter = eventMaxID + 1 })
.ToList();
I'm not sure how to use the second parameter for the Select method.
Any help would be appreciated! Thanks.

In the second form of Select that you're using, ixc is the index of the item in the collection. You'll need to add that as well as the previous max Id. That way you shouldn't have to worry about assigning to Iter either (it appears you're just using it as some kind of counter) so I've removed it.
var autoIncrementedEvents = events.Where(e => e.id == 0)
.Select((e, ixc) =>
{
e.id = eventMaxId + 1 + ixc;
return e;
})
.ToList();
Note that the way your code is written the result of this Linq statment is thrown away. You'll want to assign it to something like I've done above.
I'm not going to comment on the validity of this as an overall approach in a web setting (race conditions, duplicate ids, etc). Ideally your datastore should be assigning the Id.

How to sort a list after AddRange?

new to C#, SQL and Linq. I have two lists, one "dataTransactions" (fuel from gas stations) and a similar one "dataTransfers" (fuel from slip tanks).
They each access a different table from SQL and get combined later.
List<FuelLightTruckDataSource> data = new List<FuelLightTruckDataSource>();
using (SystemContext ctx = new SystemContext())
{
List<FuelLightTruckDataSource> dataTransactions
= ctx.FuelTransaction
.Where(tx => DbFunctions.TruncateTime(tx.DateTime) >= from.Date && DbFunctions.TruncateTime(tx.DateTime) <= to.Date
//&& tx.AssetFilled.AssignedToEmployee.Manager
&& tx.AssetFilled.AssignedToEmployee != null
//&
&& tx.AssetFilled.AssetType.Code == "L"
&& (tx.FuelProductType.FuelProductClass.Code == "GAS" || tx.FuelProductType.FuelProductClass.Code == "DSL"))
.GroupBy(tx => new { tx.AssetFilled, tx.DateTime, tx.FuelProductType.FuelProductClass, tx.FuelCard.FuelVendor, tx.City, tx.Volume, tx.Odometer}) //Added tx.volume to have individual transactions
.Select(g => new FuelLightTruckDataSource()
{
Asset = g.FirstOrDefault().AssetFilled,
Employee = g.FirstOrDefault().AssetFilled.AssignedToEmployee,
ProductClass = g.FirstOrDefault().FuelProductType.FuelProductClass,
Vendor = g.FirstOrDefault().FuelCard.FuelVendor,
FillSource = FuelFillSource.Transaction,
Source = "Fuel Station",
City = g.FirstOrDefault().City.ToUpper(),
Volume = g.FirstOrDefault().Volume,
Distance = g.FirstOrDefault().Odometer,
Date = g.FirstOrDefault().DateTime
})
.ToList();
In the end, I use
data.AddRange(dataTransactions);
data.AddRange(dataTransfers);
to put the two lists together and generate a fuel consumption report.
Both lists are individually sorted by Date, but after "AddRange" the "dataTransfers" just gets added to the end, losing my sort by Date. How do I sort the combined result again by date after using the "AddRange" command?

Try this:
data = data.OrderBy(d => d.Date).ToList();
Or if you want to order descending:
data = data.OrderByDescending(d => d.Date).ToList();

You can call List<T>.Sort(delegate).
https://msdn.microsoft.com/en-us/library/w56d4y5z(v=vs.110).aspx
Example:
data.Sort(delegate(FuelLightTruckDataSource x, FuelLightTruckDataSource y)
{
// your sort logic here.
});
Advantage: this sort doesn't create a new IList<T> instance as it does in OrderBy. it's a small thing, but to some people this matters, especially for performance and memory sensitive situations.

C# Collection Filtering, where do I begin

I have a collection lets call it 'Users', aka a set of USER
A USER has a set of CONTACTs.
I simply want to get all CONTACTs for a given user in common with another user.
I'm learning about Lambda/Linq expressions but not sure if thats what I should be doing to solve this sort of collection filtering problem.
So really I'm just looking for a intersection of 2 sets.

You can't simply do "==" on two collections. However, if the contacts have some kind of id and a user can't have the same contact twice, this is pretty easy to do:
User user = ...
var contactIds = user.Contacts.Select(c => c.Id).ToArray();
var usersWithMatchingContacts = this.unitOfWork.UserRepository.Get()
// basically, we're checking that the number of matching contacts is the same as the
// total number of contacts for the user, which means that the user has the same
// set of contacts. If you just want to require some overlap, change
// the "== u.Contacts.Count" to "> 0"
.Where(u => u.Contacts.Count(c => contactIds.Contains(c.Id)) == u.Contacts.Count);

//input data
var firstId = 12;
var secondId = 23;
var firstUser = users.First(user => user.Id == firstId);
var secondUser = users.First(user => user.Id == secondId);
var commonContacts = firstUser.Contacts
.Where(contact =>
secondUser.Contacts.Contains(contact))

Use LINQs Intersect method
var commonContacts = firstUser.Contacts.Intersect(secondUser.Contacts)

`from..where` or `FirstOrDefault` in LINQ

Traditionally, when I've tried to get data for a user from a database, and I've used the following method (to some degree):
DbUsers curUser = context.DbUsers.FirstOrDefault(x => x.u_LoginName == id);
string name = curUser.u_Name;
string email = curUser.u_Email;
You can see that all I want to do is get the Name and Email, but it seems to me that this LINQ query is getting everything stored in the database of that user, bringing it back, then allowing me to get what I want.
I have been doing some research and have found the following alternative:
var current = from s in context.DbUsers
where s.u_LoginName == id
select new {
name = s.u_Name,
email = s.u_Email
};
foreach (var user in current)
{
//Stuff Here
}
Which would be better, if any at all? Is there a lighter method to use when I only want to retrieve a few results / data?

If you want to get only two fields, then you should project your entity before query gets executed (and in this case query gets executed when you call FirstOrDefault). Use Select operator for projection to anonymous object with required fields:
var user = context.DbUsers
.Where(u => u.u_LoginName == id)
.Select(u => new { u.u_Name, u.u_Email })
.FirstOrDefault(); // query is executed here
string name = user.u_Name; // user is anonymous object
string email = user.u_Email;
That will generate SQL like:
SELECT TOP 1 u_Name, u_Email FROM DbUsers
WHERE u_LoginName = #id
In second case you are doing projection before query gets executed (i.e. enumeration started). That's why only required fields are loaded. But query will be slightly different (without TOP 1). Actually if you will convert second approach to lambda syntax, it will be almost same:
var query = context.DbUsers
.Where(u => u.u_LoginName == id)
.Select(u => new { u.u_Name, u.u_Email });
// query is defined but not executed yet
foreach (var user in query) // executed now
{
//Stuff Here
}
And just to show complete picture, without projection you get all fields of first found user:
DbUsers user = context.DbUsers
.Where(u => u.u_LoginName == id)
.FirstOrDefault(); // query is executed here
string name = user.u_Name; // user is DbUsers entity with all fields mapped
string email = user.u_Email;
In that case user entity is not projected before query is executed and you'll get all fields of user loaded from database and mapped to user entity:
SELECT TOP 1 u_LoginName, u_Name, u_Email /* etc */ FROM DbUsers
WHERE u_LoginName = #id

The second is better. You only get the needed data from database so the network traffic is lighter.
You can have the same result with extension methods:
var user = context.DbUsers
.Where(x => x.u_LoginName == id)
.Select(x => new {...})
.FirstOrDefault();

If you need not whole entity, but some values from it, then use new {name = s.u_Name, email = s.u_Email}. Because, this object is much "lighter" for cunstruction.
When you get entity with FirstOrDefault, it' saved in DBContext, but you don't do anything with it.
So, i advice you to get only data you need.

Adding where clause to nested Linq selects

I'm still new to Linq so if you see something I really shouldn't be doing, please feel free to suggest a change.
I am working on a new system to allow officers to sign up for overtime. Part of the data is displayed on a map with search criteria filtering unwanted positions. In order to make the data easier to work with, it is read into a hierarchy object structure using Linq. In this example, a job can contain multiple shifts and each shift can have multiple positions available. The Linq statement to read them in looks like the following.
var jobs = (from j in db.Job
join s in db.Shift on j.Id equals s.JobId into shifts
select new JobSearchResult
{
JobNumber = j.Id,
Name = j.JobName,
Latitude = j.LocationLatitude,
Longitude = j.LocationLongitude,
Address = j.AddressLine1,
Shifts = (from shift in shifts
join p in db.Position on shift.Id equals p.ShiftId into positions
select new ShiftSearchResult
{
Id = shift.Id,
Title = shift.ShiftTitle,
StartTime = shift.StartTime,
EndTime = shift.EndTime,
Positions = (from position in positions
select new PositionSearchResult
{
Id = position.Id,
Status = position.Status
}).ToList()
}).ToList()
});
That works fine and has been tested. There may be a better way to do it and if you know of a way, feel free to suggest. My problem is this. After the query is created, search criteria will be added. I know that I could add it when the query is created but for this its easier to do it after. Now, I can easy add criteria that looks like this.
jobs = jobs.Where(j => j.JobNumber == 1234);
However, I am having trouble figuring out how to do the same for Shifts or Positions. In other words, how would I could it to add the condition that a shift starts after a particular time? The following example is what I am trying to accomplish but will not (obviously) work.
jobs = jobs.Shifts.Where(s = s.StartTime > JobSearch.StartTime) //JobSearch.StartTime is a form variable.
Anyone have any suggestions?

Step 1: create associations so you can have the joins hidden behind EntitySet properties.
http://msdn.microsoft.com/en-us/library/bb629295.aspx
Step 2: construct your filters. You have 3 queryables and the possibility of filter interaction. Specify the innermost filter first so that the outer filters may make use of them.
Here are all jobs (unfiltered). Each job has only the shifts with 3 open positions. Each shift has those open positions.
Expression<Func<Position, bool>> PositionFilterExpression =
p => p.Status == "Open";
Expression<Func<Shift, bool>> ShiftFilterExpression =
s => s.Positions.Where(PositionFilterExpression).Count == 3
Expression<Func<Job, bool>> JobFilterExpression =
j => true
Step 3: put it all together:
List<JobSearchResult> jobs = db.Jobs
.Where(JobFilterExpression)
.Select(j => new JobSearchResult
{
JobNumber = j.Id,
Name = j.JobName,
Latitude = j.LocationLatitude,
Longitude = j.LocationLongitude,
Address = j.AddressLine1,
Shifts = j.Shifts
.Where(ShiftFilterExpression)
.Select(s => new ShiftSearchResult
{
Id = s.Id,
Title = s.ShiftTitle,
StartTime = s.StartTime,
EndTime = s.EndTime,
Positions = s.Positions
.Where(PositionFilterExpression)
.Select(p => new PositionSearchResult
{
Id = position.Id,
Status = position.Status
})
.ToList()
})
.ToList()
})
.ToList();