Linq Limit/Group by Id when joining IQueryables - entity-framework

Question

I have a list of ids, that I then have multiple IQueryables that at the end I am joining to return my results. However some of these queries could have multiple records for that particular ID and I only need 1 record per ID from my set of x IDs. For example there could be 1 Name record, 3 Addresses, 2 Emails, 4 Phones for a single ID, but I only need 1 of each, does not matter which if multiple exist.
var clientNames = (
from n in db.Names
join cnl in db.ClientNameLinks on n.name_id equals cnl.name_id
where request.Ids.Contains(cnl.client_id)
&& n.name_id > 0
&& n.nametype_id != null
select new
{
n.display_name,
cnl.client_id
});
var clientAddresses = (
from a in db.Addresses
join cal in db.ClientAddressLinks on a.address_id equals cal.address_id
where request.Ids.Contains(cal.client_id)
&& a.address_id > 0
select new {
a.display_address,
cal.client_id
});
var clientEmails = (
from e in db.Emails
join cel in db.ClientEmailLinks on e.email_id equals cel.email_id
where request.Ids.Contains(cel.client_id)
&& e.email_id > 0
select new {
e.email_address,
cel.client_id
});
var clientPhones = (
from p in db.Phones
join cpl in db.ClientPhoneLinks on p.phone_id equals cpl.phone_id
where request.Ids.Contains(cpl.client_id)
&& p.phone_id > 0
select new {
p.phone_num,
cpl.client_id
});
var rows = await (
from n in clientNames
join a in clientAddresses on n.client_id equals a.client_id into n_a
from na in n_a.DefaultIfEmpty() //LEFT JOIN
join e in clientEmails on n.client_id equals e.client_id into n_e
from ne in n_e.DefaultIfEmpty() //LEFT JOIN
join ph in clientPhones on n.client_id equals ph.client_id into n_p
from np in n_p.DefaultIfEmpty() //LEFT JOIN
select new PiiDiamondClient
{
ClientId = n.client_id,
DisplayName = n.display_name,
DisplayAddress = na.display_address,
EmailAddress = ne.email_address,
PhoneExtension = np.phone_ext,
PhoneNumber = np.phone_num
}).Distinct().ToListAsync();
return rows.OrderBy(x => x.ClientId).ToList();

Answer 1

Your last query can be rewritten in the following way. It will exactly get one record from JOIN which can multiply result set.
var query =
from n in clientNames
from a in clientAddresses.Where(a => n.client_id == a.client_id)
.Take(1).DefaultIfEmpty() //OUTER APPLY or LEFT JOIN on ROW_NUMBER query
from e in clientEmails.Where(e => n.client_id == e.client_id)
.Take(1).DefaultIfEmpty() //OUTER APPLY or LEFT JOIN on ROW_NUMBER query
from ph in clientPhones.Where(ph => n.client_id == ph.client_id)
.Take(1).DefaultIfEmpty() //OUTER APPLY or LEFT JOIN on ROW_NUMBER query
select new PiiDiamondClient
{
ClientId = n.client_id,
DisplayName = n.display_name,
DisplayAddress = a.display_address,
EmailAddress = e.email_address,
PhoneExtension = ph.phone_ext,
PhoneNumber = ph.phone_num
};