Multiple Linq (Extension Method) Joins With Anonymous Types

Question

In C#, I'm attempting to do multiple extension-method joins, in which the second join is with an enumerable of an anonymous type produced by the first join:

List<Contact> filteredContactList = GetFullContacts()
    .Join(GetContactCompanyRoles()
        , ct => ct.IdContact
        , ctCmpRole => ctCmpRole.IdContact
        , (ct, ctCmpRole) => new { Contact = ct, ContactType = ctCmpRole.ContactType })
    .Join(GetContactRoles()
        , ctf => new { ctf.Contact.IdContact, ctf.ContactType }
        , ctRole => new { ctRole.ContactId, ctRole.ContactType }
        , (ctf, ctRole) => new { Contact = ctf.Contact, PrimaryInd = ctRole.IsPrimary})
    .Select(rec => rec.Contact)
    .ToList();

ct and ctf.Contact is of Type Contact.

I am, however, getting the following error when attempting to compile:

The type arguments for method 'System.Linq.Enumerable.Join...' cannot be inferred from the usage. Try specifying the type argument explicitly.

Is there a way to get around this error without having to create an actual class for the anonymous type from the first join? Are there other options that I am not considering?

I would recommend writing the linq statement with query syntax instead as it is both easier to read and write (in my opinion). — Magnus
– Magnus, Commented Mar 23, 2015 at 22:09
I much prefer the extension methods, I personally find them much easier to read. Also a nice feature of using extension methods is that you can break these into multiple lines of code in order to get a clearer error message from the compiler. — user700390
– user700390, Commented Mar 23, 2015 at 22:10
Ahhh... that old argument. "Method syntax vs. Query Syntax" (I'm a query syntax person for Joins .. method syntax when no joins are required .. ). — Simon Whitehead
– Simon Whitehead, Commented Mar 23, 2015 at 22:11
@SimonWhitehead I do use both but Join and GroupJoin I feel is quite messy to write in lambda. — Magnus
– Magnus, Commented Mar 23, 2015 at 22:14
My understanding is that should work as long as each member of each anonymous type has the same type and name. — user700390
– user700390, Commented Mar 23, 2015 at 23:00

user700390 · Accepted Answer · 2015-03-23 23:16:23Z

3

I notice an apparent typographical error here:

    , ctRole => new { ctRole.IdContact, ctRole.ConatactType }

where perhaps you mean this:

    , ctRole => new { ctRole.IdContact, ctRole.ContactType }

i.e. use ContactType instead of ConatactType.

After this was resolved, through comment / chat we determined that compiler errors were still occurring because some of the anonymous classes being used to set up the multi-key joins did not have the same member names. In other words, instead of:

   , ctf => new { ctf.Contact.IdContact, ctf.ContactType }
    , ctRole => new { ctRole.ContactId, ctRole.ContactType }

The member names needed to be normalized between the two anyonymous classes:

   , ctf => new { ContactID = ctf.Contact.IdContact, ctf.ContactType }
    , ctRole => new { ContactID = ctRole.ContactId, ctRole.ContactType }

edited Mar 23, 2015 at 23:16

answered Mar 23, 2015 at 22:10

user700390

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1 Comment

Mackers Over a year ago

Thank you for catching the typo

Mackers · Accepted Answer · 2015-03-23 23:21:01Z

0

With the help of Vincent Ugenti, it was determined that the compiler could not evaluate the two anonymous types in the join clause arguments for the second join due to a mismatch in property names. When adding

ContactID =

to both of the anonymous initializers, the code was able to compile.

.Join(GetContactRoles()
    , ctf => new { ContactID = ctf.Contact.IdContact, ctf.ContactType }
    , ctRole => new { ContactID = ctRole.ContactId, ctRole.ContactType }
    , (ctf, ctRole) => new { Contact = ctf.Contact, PrimaryInd = ctRole.IsPrimary})

answered Mar 23, 2015 at 23:21

Mackers

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