From f8c7a579ff09e79cb94a9b034666008aee8b17a5 Mon Sep 17 00:00:00 2001
From: Derek Gray <dgray90@live.com>
Date: Thu, 9 Feb 2017 14:27:58 -0600
Subject: [PATCH] Push down subquery before using COUNT/COUNT_BIG if the query
 has an offset (fixes #7523)

---
 .../RelationalResultOperatorHandler.cs        | 10 ++++++
 .../AsyncQueryTestBase.cs                     | 27 +++++++++++++++
 .../QueryTestBase.cs                          | 14 ++++++++
 .../QuerySqlServerTest.cs                     | 34 +++++++++++++++++++
 4 files changed, 85 insertions(+)

diff --git a/src/Microsoft.EntityFrameworkCore.Relational/Query/Internal/RelationalResultOperatorHandler.cs b/src/Microsoft.EntityFrameworkCore.Relational/Query/Internal/RelationalResultOperatorHandler.cs
index a7f04c66046..dd6f558ffc3 100644
--- a/src/Microsoft.EntityFrameworkCore.Relational/Query/Internal/RelationalResultOperatorHandler.cs
+++ b/src/Microsoft.EntityFrameworkCore.Relational/Query/Internal/RelationalResultOperatorHandler.cs
@@ -379,6 +379,11 @@ var collectionSelectExpression
 
         private static Expression HandleCount(HandlerContext handlerContext)
         {
+            if (handlerContext.SelectExpression.Offset != null)
+            {
+                handlerContext.SelectExpression.PushDownSubquery();
+            }
+
             handlerContext.SelectExpression
                 .SetProjectionExpression(
                     new SqlFunctionExpression(
@@ -579,6 +584,11 @@ private static Expression HandleLast(HandlerContext handlerContext)
 
         private static Expression HandleLongCount(HandlerContext handlerContext)
         {
+            if (handlerContext.SelectExpression.Offset != null)
+            {
+                handlerContext.SelectExpression.PushDownSubquery();
+            }
+
             handlerContext.SelectExpression
                 .SetProjectionExpression(
                     new SqlFunctionExpression(
diff --git a/src/Microsoft.EntityFrameworkCore.Specification.Tests/AsyncQueryTestBase.cs b/src/Microsoft.EntityFrameworkCore.Specification.Tests/AsyncQueryTestBase.cs
index 61af66f21dc..21e00de0c17 100644
--- a/src/Microsoft.EntityFrameworkCore.Specification.Tests/AsyncQueryTestBase.cs
+++ b/src/Microsoft.EntityFrameworkCore.Specification.Tests/AsyncQueryTestBase.cs
@@ -3593,6 +3593,19 @@ public virtual async Task Select_bitwise_and_with_logical_and()
             }
         }
 
+        [ConditionalFact]
+        public virtual async Task Skip_CountAsync()
+        {
+            await AssertQuery<Customer>(
+                cs => cs.Skip(7).CountAsync());
+        }
+
+        [ConditionalFact]
+        public virtual async Task Skip_LongCountAsync()
+        {
+            await AssertQuery<Customer>(
+                cs => cs.Skip(7).LongCountAsync());
+        }
 
         protected NorthwindContext CreateContext()
         {
@@ -3620,6 +3633,20 @@ private async Task AssertQuery<TItem>(
             }
         }
 
+        private async Task AssertQuery<TItem>(
+            Func<IQueryable<TItem>, Task<long>> query,
+            bool assertOrder = false)
+            where TItem : class
+        {
+            using (var context = CreateContext())
+            {
+                TestHelpers.AssertResults(
+                    new[] { await query(NorthwindData.Set<TItem>()) },
+                    new[] { await query(context.Set<TItem>()) },
+                    assertOrder);
+            }
+        }
+
         private async Task AssertQuery<TItem>(
             Func<IQueryable<TItem>, Task<bool>> query,
             bool assertOrder = false)
diff --git a/src/Microsoft.EntityFrameworkCore.Specification.Tests/QueryTestBase.cs b/src/Microsoft.EntityFrameworkCore.Specification.Tests/QueryTestBase.cs
index 5278bbe3eaf..99624bd0644 100644
--- a/src/Microsoft.EntityFrameworkCore.Specification.Tests/QueryTestBase.cs
+++ b/src/Microsoft.EntityFrameworkCore.Specification.Tests/QueryTestBase.cs
@@ -6767,6 +6767,20 @@ from e2 in ClientDefaultIfEmpty(grouping)
                       select new { City1 = e1.City, City2 = e2 != null ? e2.City : null });
         }
 
+        [ConditionalFact]
+        public virtual void Skip_Count()
+        {
+            AssertQuery<Customer>(
+                cs => cs.Skip(7).Count());
+        }
+
+        [ConditionalFact]
+        public virtual void Skip_LongCount()
+        {
+            AssertQuery<Customer>(
+                cs => cs.Skip(7).LongCount());
+        }
+
         private static IEnumerable<TElement> ClientDefaultIfEmpty<TElement>(IEnumerable<TElement> source)
         {
             return source?.Count() == 0 ? new[] { default(TElement) } : source;
diff --git a/test/Microsoft.EntityFrameworkCore.SqlServer.FunctionalTests/QuerySqlServerTest.cs b/test/Microsoft.EntityFrameworkCore.SqlServer.FunctionalTests/QuerySqlServerTest.cs
index 164a0e22209..5d44aaec62e 100644
--- a/test/Microsoft.EntityFrameworkCore.SqlServer.FunctionalTests/QuerySqlServerTest.cs
+++ b/test/Microsoft.EntityFrameworkCore.SqlServer.FunctionalTests/QuerySqlServerTest.cs
@@ -6827,6 +6827,40 @@ FROM [Employees] AS [e1]
                 Sql);
         }
 
+        public override void Skip_Count()
+        {
+            base.Skip_Count();
+
+            Assert.Equal(
+                @"@__p_0: 7
+
+SELECT COUNT(*)
+FROM (
+    SELECT [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region]
+    FROM [Customers] AS [c]
+    ORDER BY (SELECT 1)
+    OFFSET @__p_0 ROWS
+) AS [t]",
+                Sql);
+        }
+
+        public override void Skip_LongCount()
+        {
+            base.Skip_LongCount();
+
+            Assert.Equal(
+                @"@__p_0: 7
+
+SELECT COUNT_BIG(*)
+FROM (
+    SELECT [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region]
+    FROM [Customers] AS [c]
+    ORDER BY (SELECT 1)
+    OFFSET @__p_0 ROWS
+) AS [t]",
+                Sql);
+        }
+
         private const string FileLineEnding = @"
 ";