Query: translate stringColumn.FirstOrDefault() using SUBSTRING on Sql…

[dvoreckyaa]

…Server (#10912)

Summary of changes:

• Added translation of FirstOrDefault, LastOrDefault for Sql Server, SqLite, Cosmos.

The corresponding tests have been implemented, but tests for the Cosmos are disabled, for a while.

[dnfclas]

All CLA requirements met.

[dvoreckyaa]

Summary of changes:

• Added translation of FirstOrDefault, LastOrDefault for Sql Server, SqLite, Cosmos.

• The corresponding tests have been implemented, but tests for the Cosmos are disabled, for a while.

• Some cosmos tests have been updated: FirstOrDefault in projection does not do client eval.

[maumar]

this should be {true, true, true} - we want the nullability of the argument to propagate to the entire function, so that we can do the following optimization:

SUBSTRING(foo, 1, 1) IS NULL -> foo IS NULL

[maumar]

same here (actually this one doesn't matter functionally, because we already propagate nullability from the second argument, which is the same as the first, but we can do it for consistency)

[dvoreckyaa]

I've fixed issue. Could you please clarify how SUBSTRING or RIGHT/LEFT impacts on query translation. I mean SUBSTRING does not accept NULL as the argument, but RIGHT/LEFT does. Would is there be any difference If we used RIGHT/LEFT instead of SUBSTRING?

[maumar]

Perf wise, there shouldn't be much difference. LEFT/RIGHT produces smaller sql, so I we could use them instead. SUBSTRING won't accept NULL directly, but column that contains nulls or a function that evaluates to null is fine, so we still need to take nullable scenarios into account.

[dvoreckyaa]

Got it, thanks. Please review again.

[maumar]

also, please add the following tests to the NullSemanticsQueryTestBase:

        [ConditionalTheory]
        [MemberData(nameof(IsAsyncData))]
        public virtual Task Nullable_string_FirstOrDefault_compared_to_nullable_string_LastOrDefault(bool async)
        {
            return AssertQuery(
                async,
                ss => ss.Set<NullSemanticsEntity1>().Where(e => e.NullableStringA.FirstOrDefault() == e.NullableStringB.LastOrDefault()),
                ss => ss.Set<NullSemanticsEntity1>().Where(e => e.NullableStringA.MaybeScalar(x => x.FirstOrDefault())
                    == e.NullableStringB.MaybeScalar(x => x.LastOrDefault())));
        }

[maumar]

also (in FunkyDataQueryTestBase):

        [ConditionalTheory]
        [MemberData(nameof(IsAsyncData))]
        public virtual Task String_FirstOrDefault_and_LastOrDefault(bool async)
        {
            return AssertQuery(
                async,
                ss => ss.Set<FunkyCustomer>().OrderBy(e => e.Id).Select(e => new
                {
                    first = (char?)e.FirstName.FirstOrDefault(),
                    last = (char?)e.FirstName.LastOrDefault()
                }),
                ss => ss.Set<FunkyCustomer>().OrderBy(e => e.Id).Select(e => new
                {
                    first = e.FirstName.MaybeScalar(x => x.FirstOrDefault()),
                    last = e.FirstName.MaybeScalar(x => x.LastOrDefault())

                }),
                assertOrder: true,
                elementAsserter: (e, a) =>
                {
                    AssertEqual(e.first, a.first);
                    AssertEqual(e.last, a.last);
                });
        }
``

[maumar]

@dvoreckyaa please rebase-squash on latest master and apply the suggested changes - looks good otherwise

[maumar]

@dvoreckyaa thank you for the contribution!