EF Core 6, GroupBy with inner collection Sum - linq

Question

I want to create a query which will group a set by some criteria, and it will create a result set witch will contain the sum of some inner list.
This is my query, which fails:
var invoices = await _dbContext.Beneficiaries
.Where(dbEntry => dbEntry.Id == beneficiaryId && dbEntry.ProviderId == providerId)
.SelectMany(dbEntry => dbEntry.Invoices)
.GroupBy(dbEntry => dbEntry.IssueDate.Month)
.Select(dbEntry => new
{
IssueMonth = dbEntry.Key,
VAT = dbEntry.Max(invoice => invoice.VAT),
TotalPay = dbEntry.Select(invoice => invoice.InvoiceEntries.Sum(entry => entry.DelegateHourlyRate)).Max(),
TotalSell = dbEntry.Select(invoice => invoice.InvoiceEntries.Sum(entry => entry.BeneficiaryHourlyRate)).Max(),
})
.Where(group => group.IssueMonth <= _todayDate.UtcNow.Month && group.IssueMonth >= _todayDate.UtcNow.Month - (int)by)
.ToListAsync();
Following is the class hierarchy
public class Beneficiary
{
public ICollection<Invoice> Invoices { get; set; }
}
public class Invoice
{
public ICollection<InvoiceEntry> InvoiceEntries { get; set; }
}
public class InvoiceEntry
{
public decimal DelegateHourlyRate { get; set; }
public decimal BeneficiaryHourlyRate { get; set; }
}
This is the exception I'm getting with EF version 5.0.9.
The LINQ expression 'GroupByShaperExpression: KeySelector:
b.IssueDate, ElementSelector:EntityShaperExpression: EntityType:
Invoice ValueBufferExpression: ProjectionBindingExpression:
EmptyProjectionMember IsNullable: True .Max(invoice =>
invoice.InvoiceEntries.Count)' could not be translated. Either rewrite
the query in a form that can be translated, or switch to client
evaluation explicitly by inserting a call to 'AsEnumerable',
'AsAsyncEnumerable', 'ToList', or 'ToListAsync'. See
https://go.microsoft.com/fwlink/?linkid=2101038 for more information.
This is the exception I'm getting with EF version 6.0.8.
SqlException: Cannot perform an aggregate function on an expression
containing an aggregate or a subquery. Cannot perform an aggregate
function on an expression containing an aggregate or a subquery.
<ItemGroup>
<PackageReference Include="Microsoft.EntityFrameworkCore" Version="6.0.8" />
<PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="6.0.8">
<PrivateAssets>all</PrivateAssets>
<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
</PackageReference>
<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="6.0.8" />
</ItemGroup>
Another variation
var invoices2 = await _dbContext.Beneficiaries
.Where(dbEntry => dbEntry.Id == beneficiaryId && dbEntry.ProviderId == providerId)
.SelectMany(dbEntry => dbEntry.Invoices
.GroupBy(dbEntry => dbEntry.IssueDate.Month)
.Select(dbEntry => new
{
IssueMonth = dbEntry.Key,
VAT = dbEntry.Sum(invoice => invoice.VAT),
TotalPay = dbEntry.Sum(invoice => invoice.InvoiceEntries.Sum(entry => entry.DelegateHourlyRate)),
TotalSell = dbEntry.Sum(invoice => invoice.InvoiceEntries.Sum(entry => entry.BeneficiaryHourlyRate))
}))
.Where(group => group.IssueMonth <= _todayDate.UtcNow.Month && group.IssueMonth >= _todayDate.UtcNow.Month - (int)by)
.ToListAsync();
Which results in
SqlException: Cannot perform an aggregate function on an expression
containing an aggregate or a subquery. Cannot perform an aggregate
function on an expression containing an aggregate or a subquery.
Cannot perform an aggregate function on an expression containing an
aggregate or a subquery. Cannot perform an aggregate function on an
expression containing an aggregate or a subquery.

Answer 1

If I understand your query correctly, it should be another SelectMany. Rewritten query in Query Syntax for readability and change time range condition for using table indexes, if they are exist for sure.
var current = _todayDate.UtcNow;
var prev = current.Date.AddMonths(-1);
var query =
from b in _dbContext.Beneficiaries
from invoice in b.Invoices
where invoice.IssueDate <= current && invoice.IssueDate >= prev
from invoiceEntry in invoice.InvoiceEntries
group new { invoice, invoiceEntry } by new { invoice.IssueDate.Year, invoice.IssueDate.Month } into g
select new
{
IssueMonth = g.Key.Month,
VAT = g.Max(x => x.invoice.VAT),
TotalPay = g.Sum(x => x.invoiceEntry.DelegateHourlyRate),
TotalSell = g.Sum(x => x.invoiceEntry.BeneficiaryHourlyRate)
};
var invoices = query.ToList();