We Keep Coding

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 get data from a Table if they exist in another Table C# LINQ

I have a two tables Customers, and ConnectedCustomers. That means customers can connect with each other.
My question is how can I get all Customers which are related to Chris (id = 3).
I should as a results get Bob and John..
I've tried something like this:
query = _context.Customers.Where(c =>_context.ConnectedCustomers.Any(cc => cc.Connected_Customer1.Equals(3) || cc.Connected_Customer2.Equals(3)));
But this is not working it returns too many rows..
Expected result for id 3 is BOB AND JOHN because they are connected
with id 3.
Thanks guys
Cheers

var answer = (from cc in _context.ConnectedCustomers
join c1 in _context.Customers on cc.Connected_Customer1 equals c1.id
join c2 in _context.Customers on cc.Connected_Customer2 equals c2.id
where c1.id == 3 || c2.id == 3
select c1.id == 3 ? c2 : c1
).ToList();

The problem in your query is you are querying from Customer table. When you are querying through Customer, what it's doing is getting all the possible combinations of Fk with Connected_Customer1 and Connected_Customer2 which satisfies the condition.
What you should be doing is query from ConnectedCustomers.
Try this:
var result = _context.ConnectedCustomers
.Where(x => x.Connected_Customer1.Equals(3) || x.Connected_Customer2.Equals(3))
.Select(x=>x.Customers)
.ToList();

You never use the id of the user to check (c), so you have to add a condition like this :
var query = _context.Customers.Where(customer => _context.ConnectedCustomers.Any(cc =>
cc.Connected_Customer1.Equals(customer.Id) && cc.Connected_Customer2.Equals(3) ||
cc.Connected_Customer1.Equals(3) && cc.Connected_Customer2.Equals(customer.Id))).ToList();

_context.Customers.Where(c => c.Id == _context.ConnectedCustomers.Where(cc => cc.Connected_Customer1 == 3).Select(cc => cc.Connected_Customer2))
Try that.

if clause in linq c# [duplicate]

Is it possible to use If Else conditional in a LINQ query?
Something like
from p in db.products
if p.price>0
select new
{
Owner=from q in db.Users
select q.Name
}
else
select new
{
Owner = from r in db.ExternalUsers
select r.Name
}

This might work...
from p in db.products
select new
{
Owner = (p.price > 0 ?
from q in db.Users select q.Name :
from r in db.ExternalUsers select r.Name)
}

I assume from db that this is LINQ-to-SQL / Entity Framework / similar (not LINQ-to-Objects);
Generally, you do better with the conditional syntax ( a ? b : c) - however, I don't know if it will work with your different queries like that (after all, how would your write the TSQL?).
For a trivial example of the type of thing you can do:
select new {p.PriceID, Type = p.Price > 0 ? "debit" : "credit" };
You can do much richer things, but I really doubt you can pick the table in the conditional. You're welcome to try, of course...

Answer above is not suitable for complicate Linq expression.
All you need is:
// set up the "main query"
var test = from p in _db.test select _db.test;
// if str1 is not null, add a where-condition
if(str1 != null)
{
test = test.Where(p => p.test == str);
}

var result = _context.Employees
.Where(x => !x.IsDeleted)
.Where(x => x.ClientId > (clientId > 0 ? clientId - 1 : -1))
.Where(x => x.ClientId < (clientId > 0 ? clientId + 1 : 1000))
.Where(x => x.ContractorFlag == employeeFlag);
return result;
If clientId = 0 we want ALL employees,. but for any clientId between 1 and 999 we want only clients with that ID. I was having issues with seperate LINQ statements not being the same (Deleted/Clients filters need to be on all queries), so by add these two lines it works (all be it until we have 999+ clients - which would be a happy re-factor day!!

you should change like this:
private string getValue(float price)
{
if(price >0)
return "debit";
return "credit";
}
//Get value like this
select new {p.PriceID, Type = getValue(p.Price)};

my example:
companyNamesFirst = this.model.CustomerDisplayList.Where(a => a.CompanyFirst != null ? a.CompanyFirst.StartsWith(typedChars.ToLower())) : false).Select(b => b.CompanyFirst).Distinct().ToList();

If you are using LinQ with EF Core, an easy example can be this-
var orderedData = await _dbContext.ModelName
.OrderBy(c => c.Name.Length.Length > 4 ? c.Name:c.SuperTerm.Name.IndexOf(searchValue))
.ThenBy(t => t.Producer)
.TolistAsync();

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 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.