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Fix Last() on primitive collections returning the first array element #3925

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Fix Last() on primitive collections returning the first array element #3925

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15 changes: 12 additions & 3 deletions src/EFCore.PG/Query/Internal/NpgsqlUnnestPostprocessor.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -44,12 +44,17 @@ public class NpgsqlUnnestPostprocessor : ExpressionVisitor

// Find any unnest table which does not have any references to its ordinality column in the projection or orderings
// (this is where they may appear); if found, remove the ordinality column from the unnest call.
// Note that if the ordinality column is the first ordering, we can still remove it, since unnest already returns
// ordered results.
// Note that if the ordinality column is the first ordering and it is ascending, we can still remove it, since
// unnest already returns ordered results in ascending ordinality order. Descending ordinality ordering must be
// kept (along with WITH ORDINALITY), otherwise Last()/LastOrDefault() incorrectly returns the first element
// (see https://github.com/npgsql/efcore.pg/issues/3909).
if (unwrappedTable is PgUnnestExpression unnest
&& !selectExpression.Orderings.Skip(1).Select(o => o.Expression)
.Concat(selectExpression.Projection.Select(p => p.Expression))
.Any(IsOrdinalityColumn))
.Any(IsOrdinalityColumn)
&& (orderings.Count == 0
|| !IsOrdinalityColumn(orderings[0].Expression)
|| orderings[0].IsAscending))
{
if (newTables is null)
{
Expand All @@ -75,6 +80,10 @@ public class NpgsqlUnnestPostprocessor : ExpressionVisitor
orderings = orderings.Skip(1).ToList();
}
}
else if (newTables is not null)
{
newTables[i] = table;
}

bool IsOrdinalityColumn(SqlExpression expression)
=> expression is ColumnExpression { Name: "ordinality" } ordinalityColumn
Expand Down
37 changes: 37 additions & 0 deletions test/EFCore.PG.FunctionalTests/Query/PrimitiveCollectionsQueryNpgsqlTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1489,6 +1489,25 @@ FROM unnest(p."Ints") AS i(value)
""");
}

[ConditionalFact]
public virtual async Task Column_collection_Last()
{
await AssertQuery(
ss => ss.Set<PrimitiveCollectionsEntity>().Where(c => c.Ints.Last() == 10),
ss => ss.Set<PrimitiveCollectionsEntity>().Where(c => (c.Ints.Length >= 1 ? c.Ints.Last() : -1) == 10));

AssertSql(
"""
SELECT p."Id", p."Bool", p."Bools", p."DateTime", p."DateTimes", p."Enum", p."Enums", p."Int", p."Ints", p."NullableInt", p."NullableInts", p."NullableString", p."NullableStrings", p."NullableWrappedId", p."NullableWrappedIdWithNullableComparer", p."String", p."Strings", p."WrappedId"
FROM "PrimitiveCollectionsEntity" AS p
WHERE (
SELECT i.value
FROM unnest(p."Ints") WITH ORDINALITY AS i(value)
ORDER BY i.ordinality DESC NULLS LAST
LIMIT 1) = 10
""");
}

public override async Task Column_collection_FirstOrDefault()
{
await base.Column_collection_FirstOrDefault();
Expand All @@ -1504,6 +1523,24 @@ FROM unnest(p."Ints") AS i(value)
""");
}

[ConditionalFact]
public virtual async Task Column_collection_LastOrDefault()
{
await AssertQuery(
ss => ss.Set<PrimitiveCollectionsEntity>().Where(c => c.Ints.LastOrDefault() == 10));

AssertSql(
"""
SELECT p."Id", p."Bool", p."Bools", p."DateTime", p."DateTimes", p."Enum", p."Enums", p."Int", p."Ints", p."NullableInt", p."NullableInts", p."NullableString", p."NullableStrings", p."NullableWrappedId", p."NullableWrappedIdWithNullableComparer", p."String", p."Strings", p."WrappedId"
FROM "PrimitiveCollectionsEntity" AS p
WHERE COALESCE((
SELECT i.value
FROM unnest(p."Ints") WITH ORDINALITY AS i(value)
ORDER BY i.ordinality DESC NULLS LAST
LIMIT 1), 0) = 10
""");
}

public override async Task Column_collection_Single()
{
await base.Column_collection_Single();
Expand Down