Fix array projection

Fixes #278

(cherry picked from commit f27eeab)

Author: roji

src/EFCore.PG/Query/ExpressionVisitors/NpgsqlSqlTranslatingExpressionVisitor.cs

@@ -40,7 +40,7 @@ protected override Expression VisitSubQuery(SubQueryExpression expression)
             if (properties.Count == 0)
                 return null;
             var lastPropertyType = properties[properties.Count - 1].ClrType;
-            if (lastPropertyType.IsArray && lastPropertyType.GetArrayRank() == 1)
+            if (lastPropertyType.IsArray && lastPropertyType.GetArrayRank() == 1 && subQueryModel.ResultOperators.Count > 0)
             {
                 // Translate someArray.Length
                 if (subQueryModel.ResultOperators.First() is CountResultOperator)

test/EFCore.PG.FunctionalTests/Query/QueryBugTest.cs

@@ -0,0 +1,60 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.EntityFrameworkCore.Utilities;
+using Npgsql.EntityFrameworkCore.PostgreSQL.FunctionalTests;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Microsoft.EntityFrameworkCore.Query
+{
+    public class QueryBugsTest : IClassFixture<NpgsqlFixture>
+    {
+        // ReSharper disable once UnusedParameter.Local
+        public QueryBugsTest(NpgsqlFixture fixture, ITestOutputHelper testOutputHelper)
+        {
+            Fixture = fixture;
+            //Fixture.TestSqlLoggerFactory.Clear();
+            //Fixture.TestSqlLoggerFactory.SetTestOutputHelper(testOutputHelper);
+        }
+
+        protected NpgsqlFixture Fixture { get; }
+
+        [Fact]
+        public async Task Bug278()
+        {
+            using (var testStore = NpgsqlTestStore.CreateScratch())
+            using (var context = new Bug278Context(new DbContextOptionsBuilder()
+                .UseNpgsql(testStore.Connection)
+                .Options))
+            {
+                context.Database.EnsureCreated();
+                context.Entities.Add(new Bug278Entity { ChannelCodes = new[] { 1, 1 } });
+                context.SaveChanges();
+
+                var actual = await context.Entities.Select(x => new
+                {
+                    Codes = x.ChannelCodes.Select(c => (ChannelCode)c)
+                }).FirstOrDefaultAsync();
+
+                Assert.Equal(new[] { ChannelCode.Code, ChannelCode.Code }, actual.Codes);
+            }
+        }
+
+        public enum ChannelCode { Code = 1 }
+
+        public class Bug278Entity
+        {
+            public int Id { get; set; }
+            public int[] ChannelCodes { get; set; }
+        }
+
+        class Bug278Context : DbContext
+        {
+            public Bug278Context(DbContextOptions options) : base(options) {}
+            public DbSet<Bug278Entity> Entities { get; set; }
+        }
+    }
+}