Query: Fixes LINQ ToString got absorbed during translation

Microsoft.Azure.Cosmos/src/Linq/BuiltinFunctions/BuiltinFunctionVisitor.cs

@@ -65,8 +65,21 @@ public static SqlScalarExpression VisitBuiltinFunctionCall(MethodCallExpression
                 return MathBuiltinFunctions.Visit(methodCallExpression, context);
             }
 
-            // String functions
-            if (declaringType == typeof(string))
+            // ToString with String and Guid only becomes passthrough
+            if (methodCallExpression.Method.Name == "ToString" &&
+                 methodCallExpression.Arguments.Count == 0 &&
+                 methodCallExpression.Object != null && 
+                 ((methodCallExpression.Object.Type == typeof(string)) ||
+                 (methodCallExpression.Object.Type == typeof(Guid))))
+            {
+                return ExpressionToSql.VisitNonSubqueryScalarExpression(methodCallExpression.Object, context);
+            }
+
+            // String functions or ToString with Objects that are not strings and guids
+            if ((declaringType == typeof(string)) ||
+                (methodCallExpression.Method.Name == "ToString" &&
+                 methodCallExpression.Arguments.Count == 0 &&
+                 methodCallExpression.Object != null))
             {
                 return StringBuiltinFunctions.Visit(methodCallExpression, context);
             }
@@ -83,14 +96,6 @@ public static SqlScalarExpression VisitBuiltinFunctionCall(MethodCallExpression
                 return SpatialBuiltinFunctions.Visit(methodCallExpression, context);
             }
 
-            // ToString with Objects (String and Guid only)
-            if (methodCallExpression.Method.Name == "ToString" &&
-                methodCallExpression.Arguments.Count == 0 &&
-                methodCallExpression.Object != null)
-            {
-                return ExpressionToSql.VisitNonSubqueryScalarExpression(methodCallExpression.Object, context);
-            }
-
             throw new DocumentQueryException(string.Format(CultureInfo.CurrentCulture, ClientResources.MethodNotSupported, methodCallExpression.Method.Name));
         }
 

Microsoft.Azure.Cosmos/src/Linq/BuiltinFunctions/StringBuiltinFunctions.cs

@@ -327,6 +327,27 @@ protected override SqlScalarExpression VisitExplicit(MethodCallExpression method
             }
         }
 
+        private class StringVisitToString : SqlBuiltinFunctionVisitor
+        {
+            public StringVisitToString()
+                : base("ToString",
+                    true,
+                    null)
+            {
+            }
+
+            protected override SqlScalarExpression VisitImplicit(MethodCallExpression methodCallExpression, TranslationContext context)
+            {
+                if ((methodCallExpression.Arguments.Count == 0) && (methodCallExpression.Object != null))
+                {
+                    SqlScalarExpression str = ExpressionToSql.VisitNonSubqueryScalarExpression(methodCallExpression.Object, context);
+                    return SqlFunctionCallScalarExpression.CreateBuiltin(SqlFunctionCallScalarExpression.Names.ToString, str);
+                }
+
+                return null;
+            }
+        }
+
         static StringBuiltinFunctions()
         {
             StringBuiltinFunctionDefinitions = new Dictionary<string, BuiltinFunctionVisitor>
@@ -386,6 +407,10 @@ static StringBuiltinFunctions()
                     "Reverse",
                     new StringVisitReverse()
                 },
+                {
+                    "ToString",
+                    new StringVisitToString()
+                },
                 {
                     "TrimEnd",
                     new StringVisitTrimEnd()

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.EmulatorTests/BaselineTest/TestBaseline/LinqGeneralBaselineTests.TestThenByTranslation.xml

@@ -199,7 +199,7 @@ JOIN (
         SELECT VALUE MAX(t0["Amount"]) 
         FROM root 
         JOIN t0 IN root["Records"]["Transactions"])) AS v0 
-        ORDER BY (root["IsRegistered"] ? root["FamilyId"] : root["Int"]) DESC, (v0[0] % 1000) ASC
+        ORDER BY (root["IsRegistered"] ? root["FamilyId"] : ToString(root["Int"])) DESC, (v0[0] % 1000) ASC
 ]]></SqlQuery>
       <ErrorMessage><![CDATA[Status Code: BadRequest,{"errors":[{"severity":"Error","code":2206,"message":"Unsupported ORDER BY clause. ORDER BY item expression could not be mapped to a document path."}]},0x800A0B00]]></ErrorMessage>
     </Output>

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.EmulatorTests/BaselineTest/TestBaseline/LinqTranslationBaselineTests.TestStringFunctions.xml

@@ -495,6 +495,50 @@ FROM root]]></SqlQuery>
     <Output>
       <SqlQuery><![CDATA[
 SELECT VALUE SUBSTRING(root["StringField"], 0, 1) 
+FROM root]]></SqlQuery>
+    </Output>
+  </Result>
+  <Result>
+    <Input>
+      <Description><![CDATA[String constant StartsWith]]></Description>
+      <Expression><![CDATA[query.Select(doc => "str".StartsWith(doc.StringField.ToString()))]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE STARTSWITH("str", root["StringField"]) 
+FROM root]]></SqlQuery>
+    </Output>
+  </Result>
+  <Result>
+    <Input>
+      <Description><![CDATA[ToString]]></Description>
+      <Expression><![CDATA[query.Select(doc => doc.StringField.ToString())]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE root["StringField"] 
+FROM root]]></SqlQuery>
+    </Output>
+  </Result>
+  <Result>
+    <Input>
+      <Description><![CDATA[ToString]]></Description>
+      <Expression><![CDATA[query.Select(doc => doc.NumericField.ToString())]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE ToString(root["NumericField"]) 
+FROM root]]></SqlQuery>
+    </Output>
+  </Result>
+  <Result>
+    <Input>
+      <Description><![CDATA[ToString]]></Description>
+      <Expression><![CDATA[query.Select(doc => doc.GuidField.ToString())]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE root["GuidField"] 
 FROM root]]></SqlQuery>
     </Output>
   </Result>

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.EmulatorTests/LinqTranslationBaselineTests.cs

@@ -114,6 +114,7 @@ internal class DataObject : LinqTestObject
             public int? NullableField;
 #pragma warning disable CS0649 // Field is never assigned to, and will always have its default value false
             public bool BooleanField;
+            public Guid GuidField;
 #pragma warning restore // Field is never assigned to, and will always have its default value false
 
             [JsonConverter(typeof(StringEnumConverter))]
@@ -663,7 +664,11 @@ private Func<bool, IQueryable<DataObject>> CreateDataTestStringFunctions()
                 {
                     StringField = sb.ToString(),
                     Id = Guid.NewGuid().ToString(),
-                    Pk = "Test"
+                    Pk = "Test",
+
+                    // For ToString tests
+                    ArrayField = new int[] {},
+                    Point = new Point(0, 0)
                 };
             };
             Func<bool, IQueryable<DataObject>> getQuery = LinqTestsCommon.GenerateTestCosmosData(createDataObj, Records, testContainer);
@@ -757,13 +762,23 @@ public void TestStringFunctions()
                 new LinqTestInput("String constant StartsWith (case-insensitive)", b => getQuery(b).Select(doc => "sTr".StartsWith(doc.StringField, StringComparison.OrdinalIgnoreCase))),
                 // Substring
                 new LinqTestInput("Substring", b => getQuery(b).Select(doc => doc.StringField.Substring(0, 1))),
+                // ToString
+                new LinqTestInput("String constant StartsWith", b => getQuery(b).Select(doc => "str".StartsWith(doc.StringField.ToString()))),
+                new LinqTestInput("ToString", b => getQuery(b).Select(doc => doc.StringField.ToString())),
+                new LinqTestInput("ToString", b => getQuery(b).Select(doc => doc.NumericField.ToString())),
+                new LinqTestInput("ToString", b => getQuery(b).Select(doc => doc.GuidField.ToString())),
+                // For these fields, .NET ToString and CosmosDB ToString don't produce the same behavior. Manually verified that BE behavior is as expected
+                //new LinqTestInput("ToString", b => getQuery(b).Select(doc => doc.ArrayField.ToString())),
+                //new LinqTestInput("ToString", b => getQuery(b).Select(doc => doc.Point.ToString())),
+                //new LinqTestInput("ToString", b => getQuery(b).Select(doc => doc.BooleanField.ToString())),
+                //new LinqTestInput("ToString", b => getQuery(b).Select(doc => doc.UnixTime.ToString())),
                 // ToUpper
                 new LinqTestInput("ToUpper", b => getQuery(b).Select(doc => doc.StringField.ToUpper()))
             };
             this.ExecuteTestSuite(inputs);
-        }
+    }
 
-        [TestMethod]
+    [TestMethod]
         public void TestArrayFunctions()
         {
             const int Records = 100;