From 8a6afcef3d0e0d463a6edae60f2507404ccbfcf8 Mon Sep 17 00:00:00 2001
From: Andrea Canciani <ranma42@gmail.com>
Date: Fri, 5 Jul 2024 14:26:50 +0200
Subject: [PATCH] Translate `COALESCE` as `ISNULL`

`COALESCE`is a syntactic shortcut for the CASE expression. As such, the input
values are evaluated multiple times.

`ISNULL` does not have this shortcoming.

Fixes #32519.
---
 .../Internal/SqlServerQuerySqlGenerator.cs    | 37 +++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/src/EFCore.SqlServer/Query/Internal/SqlServerQuerySqlGenerator.cs b/src/EFCore.SqlServer/Query/Internal/SqlServerQuerySqlGenerator.cs
index 717d31dad4f..64c4d282642 100644
--- a/src/EFCore.SqlServer/Query/Internal/SqlServerQuerySqlGenerator.cs
+++ b/src/EFCore.SqlServer/Query/Internal/SqlServerQuerySqlGenerator.cs
@@ -200,6 +200,43 @@ protected override Expression VisitValues(ValuesExpression valuesExpression)
         return valuesExpression;
     }
 
+    /// <summary>
+    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+    ///     any release. You should only use it directly in your code with extreme caution and knowing that
+    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+    /// </summary>
+    protected override Expression VisitSqlFunction(SqlFunctionExpression sqlFunctionExpression)
+    {
+        if (sqlFunctionExpression is { IsBuiltIn: true, Arguments: not null }
+            && string.Equals(sqlFunctionExpression.Name, "COALESCE", StringComparison.OrdinalIgnoreCase))
+        {
+            var head = sqlFunctionExpression.Arguments[0];
+            if (head.TypeMapping != sqlFunctionExpression.TypeMapping)
+            {
+                head = new SqlUnaryExpression(
+                    ExpressionType.Convert,
+                    head,
+                    sqlFunctionExpression.Type,
+                    sqlFunctionExpression.TypeMapping);
+            }
+
+            sqlFunctionExpression = (SqlFunctionExpression)sqlFunctionExpression
+                .Arguments
+                .Skip(1)
+                .Aggregate(head, (l, r) => new SqlFunctionExpression(
+                    "ISNULL",
+                    arguments: [l, r],
+                    nullable: true,
+                    argumentsPropagateNullability: [false, false],
+                    sqlFunctionExpression.Type,
+                    sqlFunctionExpression.TypeMapping
+                ));
+        }
+
+        return base.VisitSqlFunction(sqlFunctionExpression);
+    }
+
     /// <summary>
     ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
     ///     the same compatibility standards as public APIs. It may be changed or removed without notice in