Join two IQueryable

Question

The C# / Entity Framework problem: I have object

Account 
{
   public string AccountId { get; set; }
   public string UserId { get; set; }
   public string CurrencyId { get; set; }
}

then I need to return all accounts on "user A" which have same currencyId as accounts for "user B"

This is simple SQL query, but I stuck with EF. This is what I tried

public IQueryable<Account> Test(string userA, string userB)
{
    var accountsA = GetAccounts().Where(x => x.UserId == userA);
    var accountsB = GetAccounts().Where(x => x.UserId == userB);

    return accountsA.Join(
            accountsB,
            acc1 => acc1.CurrencyId,
            acc2 => acc2.CurrencyId,
            (acc1, acc2) => acc1
        );
}

this query works but return a lot of duplicate accounts for userA.

I tried

public IQueryable<Account> Test(string userA, string userB)
{
    var accountsA = GetAccounts().Where(x => x.UserId == userA);
    var accountsB = GetAccounts().Where(x => x.UserId == userB);

    return accountsA.GroupJoin(
            accountsB,
            acc1 => acc1.CurrencyId,
            acc2 => acc2.CurrencyId,
            (acc1, acc2) => acc1
        );
}

but it crash with

System.InvalidOperationException
  HResult=0x80131509
  Message=Processing of the LINQ expression 'DbSet<Account>
    .Where(x => x.UserId == "userA").GroupJoin(
        outer: DbSet<Account>
            .Where(x => x.UserId == "userB"), 
        inner: acc1 => acc1.CurrencyId, 
        outerKeySelector: acc2 => acc2.CurrencyId, 
        innerKeySelector: (acc1, acc2) => acc1)' by 'NavigationExpandingExpressionVisitor' failed. This may indicate either a bug or a limitation in EF Core. See https://go.microsoft.com/fwlink/?linkid=2101433 for more detailed information.

how can I do DISTINCT on EF queries?

Answer 1

public IQueryable<Account> Test(string userA, string userB)
{
    var accountsA = GetAccounts().Where(x => x.UserId == userA);
    var accountsB = GetAccounts().Where(x => x.UserId == userB);

    return accountsA.Where(accountA => 
         accountsB.Any(accountB => accountB.CurrencyId == accountA.CurrencyId)
    );
}

Answer 2

ok, I found it. it is.Distinct()

so the answer will be

    var a1 = accountContext.Account.Where(x => x.UserId == "userA");
    var a2 = accountContext.Account.Where(x => x.UserId == "userB");
    var result = a1.Join(
            a2,
            acc1 => acc1.CurrencyId,
            acc2 => acc2.CurrencyId,
            (acc1, acc2) => acc1
        )
        .Distinct();

Answer 3

So user B has zero or more Accounts , where every Account has a CurrencyId .

"I need to return all accounts on "user A" which have same currencyId as the currencyIds of user B"

Apparently we need the CurrencyIds` of user B:

int idUserB = ...
var currencyIdsOfUserB = GetAccounts()
    .Where(account => account.Id == idUserB)
    .Select(account => account.CurrencyId)
    .Distinct();                              // only if you expect duplicates

All accounts of user A that have at least one of these currencyIds:

int idUserA:
var result = GetAccounts.Where(account => account.Id == idUserB
             && currencyIdsOfUserB.Contains(account.CurrencyId);

Accounts
Id UserId CurrencyId
01   09      18
02   10      50
03   11      19
04   20      49
05   10      51
06   10      52
07   20      52
08   20      51
09   10      50
10   20      52

• User [10] has Accounts 2, 5, 6, 9 with CurrencyIds 50, 51, 52, 50

• User [20] has Accounts 4, 7, 8, 10 with CurrencyIds 49, 52, 51, 52

• currenCyIdsOfUserB = {50, 51, 52}

• Give me all Accounts with UserId equal to [10] and CurrencyId in {50, 51, 52}. The result will be the Accounts with Id 7, 8, 10

Simple comme bonjour!