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Convert SQL to lambda in C#

How can I re-write the following query from SQL to lambda in C#? Is it recommended to write in lambda?
SELECT *
FROM Claims
WHERE id IN (SELECT claimId
FROM MissingItems
GROUP BY claimId);

Equivalent using LINQ lambdas - assuming you have a collection of MissingItem objects in your code (and a representation of Claim in your code)
List<String> distinctClaimIds = missingItems.Select(mi => mi.claimId).Distinct();
List<Claim> claimsWithThoseIds = claims.Where(c => distinctClaimIds.Contains(c.id)).ToList();
Edit for your "one statement" interest:
Closest to "one statement" (even though I think 2 is more readable) I can think of:
List<Claim> claimsWithThoseIds = claims.Where(c => missingItems.Select(mi => mi.claimId).Distinct().Contains(c.id)).ToList()

You can use Join to do this in one "line":
class MissingItems
{
public string Id {get;set;}
}
class Claims
{
public string ClaimId {get;set;}
}
void Main()
{
List<MissingItems> mi = new List<MissingItems>() {
new MissingItems() {Id = "a"},
new MissingItems() {Id = "b"},
new MissingItems() {Id = "c"},
new MissingItems() {Id = "d"},
};
List<Claims> cl = new List<Claims>() {
new Claims() {ClaimId = "a"},
new Claims() {ClaimId = "f"},
new Claims() {ClaimId = "c"},
new Claims() {ClaimId = "d"},
};
var a = mi.Join(cl, m => m.Id, c => c.ClaimId, (m,c) => {
return new { Claim = c.ClaimId, Missing = m.Id};
});
foreach(var b in a)
{
Console.WriteLine("Claim: " + b.Claim + " Missing: " + b.Missing);
}
}
This will join the ClaimId from Claims on the MissingItems Id property. The output looks like this:
Claim: a Missing: a
Claim: c Missing: c
Claim: d Missing: d

Trying to combine two tables in LINQ

Say I have a
TableA
string Name
string Description
TableB
string Name
string Value
TableA and TableB are joined by Name. (In theory, i.e. not enforced in DB)
I want to create an object:
public MyObject
{
string Name
string Description
List<string> Values
}
I'm tying to understand how to combine these using LINQ.
var tableA = _oda.GetTableA();
var tableB = _oda.GetTableB();
var model = from a in tableA
join b in tableB on a.NAME equals b.NAME
select new MyObject
{
Name= a.Name,
Description = a.Description,
Values = "<Not sure to get list of tableb.Value>"
};

If it's an inner join, you can use GroupBy after your join:
var tableA = new List<TableA> { new TableA { Name = "1", Description = "D1" }, new TableA { Name = "2", Description = "D2"} };
var tableB = new List<TableB> { new TableB { Name = "1", Value = "V1" }, new TableB { Name = "1", Value = "V2"} };
var result = tableA.Join(tableB, a => a.Name, b => b.Name, (a, b) => new { A = a, B = b})
.GroupBy(k => k.A, e => e.B.Value)
.Select(g => new MyObject
{
Name = g.Key.Name,
Description = g.Key.Description,
Values = g.ToList()
});
foreach (var res in result)
{
Console.WriteLine("Name: {0}, Description: {1}, Value: {2}", res.Name, res.Description, string.Join(", ", res.Values));
}

Didn't try the code, but something like this should work.
var result = from a in TableA
join b in TableB on a.Name equal b.Name
group b.Value by a into g
select new MyObject
{
Name = g.Key.Name,
Description = g.Key.Description,
Values = g.ToList()
}

Concatenate Int to String in LINQ Query

I have the following LINQ query.
var providers = from c in Repository.Query<Company>()
where !c.IsDeleted
select new { c.Description, Id = "C" + c.Id };
I'm trying to concatenate the ID to "C". So, for example, if c.Id is 35 then the result should be "C35".
This obviously doesn't work because you can't add an integer (c.Id) to a string. I could easily resolve this in C# using string.Format() or converting the type. But how can I do this in LINQ?

Try using SqlFunctions.StringConvert Method:
var xd = (from c in Repository.Query<Company>()
where !c.IsDeleted
select new { c.Description, Id = "C" + SqlFunctions.StringConvert((double)c.Id).Trim()});

When you need functionality of .NET only in preparing the result (as opposed to, say, filtering, which should be done on RDBMS side to avoid bringing too much data in memory) the common trick is to complete the conversion in memory using the AsEnumerable method:
var providers = Repository.Query<Company>()
.Where(c => !c.IsDeleted)
.Select(c => new { c.Description, c.Id }) // <<== Prepare raw data
.AsEnumerable() // <<== From this point it's LINQ to Object
.Select(c => new { c.Description, Id = "C"+c.Id }); // <<== Construct end result

The code that you have written will work fine. Here is a mock up of the same code and it outputs the Id's
class Company
{
public string Description { get; set; }
public int Id { get; set; }
public bool IsDeleted { get; set; }
}
static void Main()
{
//setup
var list = new List<Company>();
list.Add(new Company
{
Description = "Test",
Id = 35,
IsDeleted = false
});
list.Add(new Company
{
Description = "Test",
Id = 52,
IsDeleted = false
});
list.Add(new Company
{
Description = "Test",
Id = 75,
IsDeleted = true
});
/* code you are looking for */
var providers = from c in list
where !c.IsDeleted
select new { c.Description, Id = "C" + c.Id };
foreach (var provider in providers)
{
Console.WriteLine(provider.Id);
}
Console.ReadKey();
}

What about string format
var providers = from c in Repository.Query<Company>()
where !c.IsDeleted
select new { c.Description, Id = "C" + c.Id.ToString() };

Combining two Lists of an Object into one

I am currently developing an application that requires this senario.
Assuming I have this object
public class ObjectItem
{
public int Id {get;set;}
public int Name {get;set;}
public int Sex {get;set;}
public int Age {get;set;}
public string Complexion {get;set;}
}
If we now have two lists of this object
var studentWithAge = new List<ObjectItem>
{
new ObjectItem {Id = 1, Name = "John", Age = 2},
new ObjectItem {Id = 2, Name = "Smith", Age = 5},
new ObjectItem {Id = 3, Name = "Juliet", Age = 7},
};
var studentWithSexAndComplexion = new List<ObjectItem>
{
new ObjectItem {Id = 1, Name = "John", Sex = "Male", Complexion = "fair"},
new ObjectItem {Id = 2, Name = "Smith", Sex = "Male", Complexion = " "},
new ObjectItem {Id = 3, Name = "Juliet", Sex = "Female", Complexion = "Blonde"},
new ObjectItem {Id = 4, Name = "Shittu", Sex = "Male", Complexion = "fair"},
};
I want to merge these two lists into just one. The end result should look like this.
var CompleteStudentData=new List<ObjectItem>
{
new ObjectItem{Id=1,Name="John",Sex="Male", Complexion="fair",Age=2},
new ObjectItem{Id=2,Name="Smith",Sex="Male", Complexion=" ", Age=5},
new ObjectItem{Id=3,Name="Juliet",Sex="Female", Complexion="Blonde", Age=7},
new ObjectItem{Id=4,Name="Shittu",Sex="Male", Complexion="fair", Age=0},
}
How do i achieve this? Using Union to merge the two list does not produce the desired result. I would appreciate your help.

var result = StudentWithAge.Join(StudentWithSexAndComplexion,
sa => sa.Id,
ssc => ssc.Id,
(sa, ssc) => new ObjectItem
{
Id = sa.Id,
Name = sa.Name,
Age = sa.Age,
Sex = ssc.Sex,
Complexion = ssc.Complexion
}).ToList();
Or, avoiding creation of new objects:
var result = StudentWithAge.Join(StudentWithSexAndComplexion,
sa => sa.Id,
ssc => ssc.Id,
(sa, ssc) =>
{
sa.Sex = ssc.Sex;
sa.Complexion = ssc.Complexion;
return sa;
}).ToList();
And if you want to add students presented only in the second list, than also:
result.AddRange(StudentWithSexAndComplexion.Where(ssc => !StudentWithAge.Any(sa => sa.Id == ssc.Id)));

Since it's possible that your collections will not have a 1-to-1 correspondence, you would have to do a full outer join. See here for how you can compose it that way.
Here's one way you can get similar results.
Collect all the keys (the ids) from both collections, then perform a left join with each of the collections, then combine the results.
var ids = studentWithAge.Select(s => s.Id)
.Union(studentWithSexAndComplexion.Select(s => s.Id));
var query =
from id in ids
from sa in studentWithAge
.Where(sa => sa.Id == id)
.DefaultIfEmpty(new ObjectItem { Id = id })
from ssc in studentWithSexAndComplexion
.Where(ssc => ssc.Id == id)
.DefaultIfEmpty(new ObjectItem { Id = id })
select new ObjectItem
{
Id = id,
Name = sa.Name ?? ssc.Name,
Sex = ssc.Sex,
Age = sa.Age,
Complexion = ssc.Complexion,
};

.Net has a function which is concatenating collections:
var concatenatedCollection = StudentWithAge.Concat(StudentWithSexAndComplexion).ToList();
var StudentWithAge = new List<ObjectItem>()
{
new ObjectItem{Id=1,Name="John",Age=2},
new ObjectItem{Id=2,Name="Smith",Age=5},
new ObjectItem{Id=3,Name="Juliet",Age=7},
};
var StudentWithSexAndComplexion = new List<ObjectItem>()
{
new ObjectItem{Id=1,Name="John",Sex="Male", Complexion="fair"},
new ObjectItem{Id=2,Name="Smith",Sex="Male", Complexion=" "},
new ObjectItem{Id=3,Name="Juliet",Sex="Female", Complexion="Blonde"},
new ObjectItem{Id=4,Name="Shittu",Sex="Male", Complexion="fair"},
};
var concatenatedCollection = StudentWithAge.Concat(StudentWithSexAndComplexion).ToList();

How to make linq master detail query for 0..n relationship?

Given a classic DB structure of Orders has zero or more OrderLines and OrderLine has exactly one Product, how do I write a LINQ query to express this?
The output would be
OrderNumber - OrderLine - Product Name
Order-1 null null // (this order has no lines)
Order-2 1 Red widget
I tried this query but is not getting the orders with no lines
var model = (from po in Orders
from line in po.OrderLines
select new
{
OrderNumber = po.Id,
OrderLine = line.LineNumber,
ProductName = line.Product.ProductDescription,
}
)

Here is an article which appears to explain how to achieve exactly what you are trying to do.
public static void OuterJoinSimpleExample()
{
var customers = new List<Customer>() {
new Customer {Key = 1, Name = "Gottshall" },
new Customer {Key = 2, Name = "Valdes" },
new Customer {Key = 3, Name = "Gauwain" },
new Customer {Key = 4, Name = "Deane" },
new Customer {Key = 5, Name = "Zeeman" }
};
var orders = new List<Order>() {
new Order {Key = 1, OrderNumber = "Order 1" },
new Order {Key = 1, OrderNumber = "Order 2" },
new Order {Key = 4, OrderNumber = "Order 3" },
new Order {Key = 4, OrderNumber = "Order 4" },
new Order {Key = 5, OrderNumber = "Order 5" },
};
var q = from c in customers
join o in orders on c.Key equals o.Key into outer
from o in outer.DefaultIfEmpty()
select new {
Name = c.Name,
OrderNumber = ((o == null) ? "(no orders)" : o.OrderNumber)
};
foreach (var i in q) {
Console.WriteLine("Customer: {0} Order Number: {1}",
i.Name.PadRight(11, ' '), i.OrderNumber);
}
Console.ReadLine();
}

This is the working query (built using the example linked above):
var model = (from po in orders
join line in orderLines // note this is another var, it isn't po.Lines
on po.Id equals line.OrderId into g
from line in g.DefaultIfEmpty()
select new
{
OrderNumber = po.Id,
OrderLine = line == null ? 0 : line.LineNumber,
ProductName = line == null ? string.Empty : line.Product.ProductDescription,
}
)

var model =
from po in Orders
from line in po.OrderLines.DefaultIfEmpty()
select new
{
OrderNumber = po.Id,
OrderLine = line != null ?
(int?)line.LineNumber : null,
ProductName = line != null ?
line.Product.ProductDescription : null
} ;