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How can I use optional parameters in a query with multiple joins, using Entity Framework?

I've looked at several possible solutions to this problem, and the ones I have tried do not seem to work. One solution was to use if statements for the optional filters, which doesn't work because I have multiple joins and the where clause is in the last join.
The optional parameters are: roleId, disciplineId, resourceId, and projectName.
try
{
IQueryable<ProjectPlanHeader> bob =
(
from h in context.ProjectPlanHeaders
join r in context.ProjectPlanRevisions on h.ProjectPlanHeaderId equals r.ProjectPlanHeaderId
join a in context.PlanActivityLineItems on r.PlanRevisionId equals a.PlanRevisionId
where ((roleId == null || a.RequiredRoleId == roleId) &&
(disciplineId == null || a.DisciplineId == disciplineId) &&
(resourceId == null || a.ActualResourceId == resourceId) &&
(h.ProjectPlanName.ToLower().Contains(projectName.ToLower()) || projectName == String.Empty))
select h
)
.Include(x => x.ProjectPlanRevisions)
.ThenInclude(y => y.PlanActivityLineItem)
.ThenInclude(z => z.PlannedHours)
.Include(x => x.ActualPlanRevisions)
.ThenInclude(y => y.ActualPlanActivities)
.ThenInclude(z => z.ActualHours);
var john = bob.ToList();
return bob;
}
catch (Exception ex)
{
return null;
}
I added the try/catch so I could see what was happening, as it was silently failing. What I found was a "Object not set to an instance of an object". That's never helpful, because I don't know what object it's talking about. Can someone please show me how to do this the right way?
UPDATE: Thanks for the responses I got, but unfortunately they don't work. The problem is that I end up getting multiple headers back when I filter. This happens because there are multiple revisions for each header, and I really only need the max rev. I tried changing the initial query so that only the max rev was included, and that still did not help. There does not appear to be a solution for this issue, so I will have to do it another way.

Rewrite query to do not use explicit joins, because you have navigation properties. Also because of JOINS you have duplicated records, you will discover it later.
var query = context.ProjectPlanHeaders
.Include(x => x.ProjectPlanRevisions)
.ThenInclude(y => y.PlanActivityLineItem)
.ThenInclude(z => z.PlannedHours)
.Include(x => x.ActualPlanRevisions)
.ThenInclude(y => y.ActualPlanActivities)
.ThenInclude(z => z.ActualHours)
.AsQueryable();
if (!string.IsNullOrEmpty(projectName))
{
// here we can combine query
query = query
.Where(h => h.ProjectPlanName.ToLower().Contains(projectName.ToLower()));
}
// check that we have to apply filter on collection
if (roleId != null || disciplineId != null || resourceId != null)
{
// here we have to do filtering as in original query
query = query
.Where(h => h.ProjectPlanRevisions
.Where(r => roleId == null || r.PlanActivityLineItem.RequiredRoleId == roleId)
.Where(r => disciplineId == null || r.PlanActivityLineItem.DisciplineId == disciplineId)
.Where(r => resourceId == null || r.PlanActivityLineItem.ActualResourceId == resourceId)
.Any()
);
}
var result = query.ToList();

Let me clarify my comment with an example:
So: An IQueryable is used to build up an expression tree. They are not evaluated until enummerated (e.g. ToList or FirstOrDefault). I.e. you can conditional add Where and Includes with little to no cost before ennumerating`
Thus you could do this,
IQueryable<ProjectPlanHeader> bob =
context.ProjectPlanHeader
.Include(x => x.ProjectPlanRevisions)
.ThenInclude(y => y.PlanActivityLineItem);
if (roleId != null) {
bob =
from h in bob
join r in context.ProjectPlanRevisions on h.Id equals r.ProjectPlanHeaderId
join a in context.PlanActivityLineItems on r.Id equals a.ProjectPlanRevisionId
where a.RequiredRoleId == roleId
select h;
}
// same for the rest.
var john = bob.ToList();
writing the chained filer is not easiest, but it works

Convert SQL Query to LINQ Lambda C#

I have to fix a query which was already written in the LINQ Lambda, I found the fix in a Simple SQL Query but now I have some trouble in converting it to LINQ Query,
Here is my SQL Query
select * from RequestItem_SubRequestItem x
where x.RequestItem_key = 1 and x.SubRequestItem_key in (
select o.SubRequestItem_key
from SubRequestItem_Entitlement o
inner join SubRequestItem sr on sr.SubRequestItem_key = o.SubRequestItem_key
where o.Entitlement_key = 2 and sr.Action = 'Add' )
And below is my LINQ C# code where I am trying to insert my fixes which include inner join.
z.Entitlements = ARMContext.Context.SubRequestItem_Entitlement
.Where(o => o.Entitlement_key == z.AccessKey && !o.Role_key.HasValue && o.Entitlement.EntitlementConfiguration.UserVisible == true
&& (ARMContext.Context.RequestItem_SubRequestItem
.Where(x => x.RequestItem_key == requestItemKey)
.Select(y => y.SubRequestItem_key)
.Contains(o.SubRequestItem_key)))
.Join(ARMContext.Context.SubRequestItems, subrq => subrq.SubRequestItem_key, temp => requestItemKey, (subrq, temp) => subrq == temp)
Where as previously the C# LINQ code looked like this
z.Entitlements = ARMContext.Context.SubRequestItem_Entitlement
.Where(o => o.Entitlement_key == z.AccessKey && !o.Role_key.HasValue && o.Entitlement.EntitlementConfiguration.UserVisible == true
&& (ARMContext.Context.RequestItem_SubRequestItem
.Where(x => x.RequestItem_key == requestItemKey)
.Select(y => y.SubRequestItem_key)
.Contains(o.SubRequestItem_key)))
When I try to insert the JOIN in the LINQ as per my conditions then I get to see this error.
What is my mistake? Can anybody tell me a correct way to do it?

I think this should Suffice your need, although you might have to make changes to the other code which are dependent on your SubRequestItem_Entitlement table with {user, add}
please have a look at that. As I am sure you will have to make those changes.
.Join(ARMContext.Context.SubRequestItems, user => user.SubRequestItem_key, subreqItems => subreqItems.SubRequestItem_key, (user, subreqItems) => new { user, subreqItems })
.Where(Action => Action.subreqItems.Action == z.ApprovalAction)

you can use this query. I exactly matched the SQL query
var query = ARMContext.Context.RequestItem_SubRequestItem
.Where(a => a.RequestItem_key == 1 && a.RequestItem_key == (ARMContext.Context.SubRequestItem_Entitlement
.Join(ARMContext.Context.SubRequestItems,
right => right.SubRequestItem_key,
left => left.SubRequestItem_key,
(right, left) => new
{
right = right,
left = left
})
.Where(x => x.right.Entitlement_key == 2 && x.left.Action == "Add" && x.right.SubRequestItem_key == a.RequestItem_key).Select(y => y.right.SubRequestItem_key)).FirstOrDefault());

how to use linq to return a value from 4 tables

I am reasonably new to Linq and it seems quite easy to iuse but I am having an issue when trying to extract a value from a table that is linked/constrained by 3 other tables.
I have this in my SQL DB:
I am using Asp.Net 4 and Entity Framework 6.
I have as a parameter the 'DatabaseName'.
I ultimately want to get the SubscriptionRef that is assigned to this name.
I could do this step-by-step (ie using multiple linqs) but I thought it would look 'clean' using just 1 linq statment.
I have got as far as this:
var names = o.RegisteredNames.Where(d => d.DatabaseName == DBName).Where(d => d.ClientNames.Where(f => f.ClientId == f.Client.ClientId).FirstOrDefault();
But I get the error:
Cannot implicitly convert type 'Services.ClientName' to 'bool'

You have a Problem here:
d => d.ClientNames.Where(f => f.ClientId == f.Client.ClientId)
f => ... returns a single ClientName or null, which causes your error, because there should be a boolean.
If you want this first value or null, you should replace
.Where(d => d.ClientNames ...
//with
.Select(d => d.ClientNames ...

Try this:
o.RegisteredNames.First(d => d.DatabaseName == DBName).ClientNames.Select(x=>x.Client.Subscription.SubscriptionRef)
It should give you list go SubscriptionRef.

You can try with one LINQ query like...
var names = o.RegisteredNames.Where(d => d.DatabaseName == DBName ).FirstOrDefault();

You might wanna try sql style:
var client = from c in db.Clients
join cn in db.ClientNames on c.ClientId equals cn.ClientId
join rn in db.RegisteredNames on cn.RegisteredNamesId equals rn.RegisteredNameId
where rn.DatabaseName == "YourDBName"
select c;
But it also depends on how your objects were built.

Try using join:
var names = (
from names in o.RegisteredNames.Where(d => d.DatabaseName == DBName)
join cnames in o.ClientNames on names.RegisteredNamesId equals cnames.RegisteredNamesId
select cnames.ClientId
).FirstOrDefault();
Add as many joins as you want.

Try this
It works in List,
var option1= o.RegisteredNames
.Where(g => g.DbName == "YourDbName")
.Where(h => h.ClientNames.Any(f => f == 5))
.FirstOrDefault();
var option2= o.RegisteredNames
.FirstOrDefault(h => h.DbName == "Name" && h.ClientNames.Any(j => j == 1));

LINQ query from two related lists with specific criteria

Using SQL Server and C#:
I have 3 tables: Employee (EmployeeId, JobDescription), CashAllowance (CashAllowanceId) and EmployeeCashAllowance (EmployeeId, CashAllowanceId, ValueTaken, DateAdded).
Employee has (EmployeeeId) as primary key, CashAllowance has (CashAllowanceId) as primary key, EmployeeCashAllowance has 2 foreign keys (EmployeeId and CashAllowanceId) related to the first 2 tables.
I need to get the list of (EmployeeCashAllowance) in a specific date + for specific CashAllowanceId + for employees having JobDescription = "Dev"
I need to achieve this in a LINQ query on lists filled from DB where list of all EmployeeCashAllowance is a property of the Employee object (each Employee object has List ListEmployeeCashAllowances as a property). What I wrote was this:
var sumValues = (from e in Employees
where (e.JobDescription == "Dev")
from c in e.ListEmployeeCashAllowances
where (c.EmployeeId == e.EmployeeId && c.CashAllowanceId == selectedCashAllowanceId && c.DateAdded == selectedDate)
select c).ToList();
But this is not working as I expected, it's returning all rows in Employee and EmployeeCashAllowance whatever the selected criteria is (even is JobDescription is not Dev and CashAllowanceId is not the selectedCashAllowanceId).
Where did I go wrong with this?

You better use join I suppose try something like this , I haven't tested so it must look like this
var sumValues = (from e in Employees
join c in EmployeeCashAllowances on e.EmployeeId equals c.EmployeeId
where ( c.CashAllowanceId == selectedCashAllowanceId && c.DateAdded == selectedDate && e.JobDescription == "Dev")
select c).ToList();

Not Tested, Just gave a try
var results = from e in Employees
from ec in e.EmployeeCashAllowances
where (e.EmployeeId == ec.EmployeeId && ec.CashAllowanceId == selectedCashAllowanceId && ec.DateAdded == selectedDate && e.JobDescription == "Dev")
select ec;

Well, I didn't expect this, but I had to change from the query to get what I want, with the restriction that I had use "Sum" and get sum of values in the list of EmployeeCashAllowance resulted:
Employees.SelectMany(e => e.ListEmployeeCashAllowances).Where(lc => lc.CashAllowanceId == selectedCashAllowanceId).Select(c => c.ValueTaken).Sum();
Note that if I don't use Sum the list returned will contain all items in all the ListEmployeeCashAllowances.

It becomes clear when you clean the formatting:
var sumValues =
from e in Employees
where
e.JobDescription == "Dev"
from c in e.ListEmployeeCashAllowances // Gotcha!!!
where
c.EmployeeId == e.EmployeeId && // Is that really necessary?
c.CashAllowanceId == selectedCashAllowanceId &&
c.DateAdded == selectedDate
select c;
Normally I use LINQ methods like:
var query = Employees
.Where(e => e.JobDescription == "Dev")
.SelectMany(e => e.ListEmployeeCashAllowances)
.Where(c =>
c.CashAllowanceId == selectedCashAllowanceId &&
c.DateAdded == selectedDate);
But 'e.ListEmployeeCashAllowances' still can be selecting all users...
A long shot, without knowing your environment, could be:
var query = Employees
.SelectMany(e => e.ListEmployeeCashAllowances)
.Where(c =>
c.JobDescription == "Dev" &&
c.CashAllowanceId == selectedCashAllowanceId &&
c.DateAdded == selectedDate);
Resolving what to do with 'query', you can simply do:
var sumValues = query.Sum(c => c.ValueTaken);

LINQ Using Max() to select a single row

I'm using LINQ on an IQueryable returned from NHibernate and I need to select the row with the maximum value(s) in a couple of fields.
I've simplified the bit that I'm sticking on. I need to select the one row from my table with the maximum value in one field.
var table = new Table { new Row(id: 1, status: 10), new Row(id: 2, status: 20) }
from u in table
group u by 1 into g
where u.Status == g.Max(u => u.Status)
select u
This is incorrect but I can't work out the right form.
BTW, what I'm actually trying to achieve is approximately this:
var clientAddress = this.repository.GetAll()
.GroupBy(a => a)
.SelectMany(
g =>
g.Where(
a =>
a.Reference == clientReference &&
a.Status == ClientStatus.Live &&
a.AddressReference == g.Max(x => x.AddressReference) &&
a.StartDate == g.Max(x => x.StartDate)))
.SingleOrDefault();
I started with the above lambda but I've been using LINQPad to try and work out the syntax for selecting the Max().
UPDATE
Removing the GroupBy was key.
var all = this.repository.GetAll();
var address = all
.Where(
a =>
a.Reference == clientReference &&
a.Status == ClientStatus.Live &&
a.StartDate == all.Max(x => x.StartDate) &&
a.AddressReference == all.Max(x => x.AddressReference))
.SingleOrDefault();

I don't see why you are grouping here.
Try this:
var maxValue = table.Max(x => x.Status)
var result = table.First(x => x.Status == maxValue);
An alternate approach that would iterate table only once would be this:
var result = table.OrderByDescending(x => x.Status).First();
This is helpful if table is an IEnumerable<T> that is not present in memory or that is calculated on the fly.

You can also do:
(from u in table
orderby u.Status descending
select u).Take(1);

You can group by status and select a row from the largest group:
table.GroupBy(r => r.Status).OrderByDescending(g => g.Key).First().First();
The first First() gets the first group (the set of rows with the largest status); the second First() gets the first row in that group.
If the status is always unqiue, you can replace the second First() with Single().

Addressing the first question, if you need to take several rows grouped by certain criteria with the other column with max value you can do something like this:
var query =
from u1 in table
join u2 in (
from u in table
group u by u.GroupId into g
select new { GroupId = g.Key, MaxStatus = g.Max(x => x.Status) }
) on new { u1.GroupId, u1.Status } equals new { u2.GroupId, Status = u2.MaxStatus}
select u1;

What about using Aggregate?
It's better than
Select max
Select by max value
since it only scans the array once.
var maxRow = table.Aggregate(
(a, b) => a.Status > b.Status ? a : b // whatever you need to compare
);

More one example:
Follow:
qryAux = (from q in qryAux where
q.OrdSeq == (from pp in Sessao.Query<NameTable>() where pp.FieldPk
== q.FieldPk select pp.OrdSeq).Max() select q);
Equals:
select t.* from nametable t where t.OrdSeq =
(select max(t2.OrdSeq) from nametable t2 where t2.FieldPk= t.FieldPk)

Simply in one line:
var result = table.First(x => x.Status == table.Max(y => y.Status));
Notice that there are two action.
the inner action is for finding the max value,
the outer action is for get the desired object.