Query: Adds DOCUMENTID extension method for LINQ

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

@@ -50,11 +50,16 @@ public static SqlScalarExpression VisitBuiltinFunctionCall(MethodCallExpression
 
                 if (methodCallExpression.Method.DeclaringType.GeUnderlyingSystemType() == typeof(CosmosLinqExtensions))
                 {
-                    // CosmosLinq Extensions are either RegexMatch or Type check functions (IsString, IsBool, etc.)
+                    // CosmosLinq Extensions can be RegexMatch, DocumentId or Type check functions (IsString, IsBool, etc.)
                     if (methodCallExpression.Method.Name == nameof(CosmosLinqExtensions.RegexMatch))
                     {
                         return StringBuiltinFunctions.Visit(methodCallExpression, context);
-                    }
+                    }
+
+                    if (methodCallExpression.Method.Name == nameof(CosmosLinqExtensions.DocumentId))
+                    {
+                        return OtherBuiltinSystemFunctions.Visit(methodCallExpression, context);
+                    }
 
                     return TypeCheckFunctions.Visit(methodCallExpression, context);
                 }

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

@@ -0,0 +1,38 @@
+//------------------------------------------------------------
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+//------------------------------------------------------------
+
+namespace Microsoft.Azure.Cosmos.Linq
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Globalization;
+    using System.Linq.Expressions;
+    using Microsoft.Azure.Cosmos.SqlObjects;
+
+    internal static class OtherBuiltinSystemFunctions
+    {
+        private static Dictionary<string, BuiltinFunctionVisitor> FunctionsDefinitions { get; set; }
+
+        static OtherBuiltinSystemFunctions()
+        {
+            FunctionsDefinitions = new Dictionary<string, BuiltinFunctionVisitor>
+            {
+                [nameof(CosmosLinqExtensions.DocumentId)] = new SqlBuiltinFunctionVisitor(
+                    sqlName: "DOCUMENTID",
+                    isStatic: true,
+                    argumentLists: new List<Type[]>()
+                    {
+                        new Type[]{typeof(object)},
+                    })
+            };
+        }
+
+        public static SqlScalarExpression Visit(MethodCallExpression methodCallExpression, TranslationContext context)
+        {
+            return FunctionsDefinitions.TryGetValue(methodCallExpression.Method.Name, out BuiltinFunctionVisitor visitor)
+                ? visitor.Visit(methodCallExpression, context)
+                : throw new DocumentQueryException(string.Format(CultureInfo.CurrentCulture, ClientResources.MethodNotSupported, methodCallExpression.Method.Name));
+        }
+    }
+}

Microsoft.Azure.Cosmos/src/Linq/CosmosLinqExtensions.cs

@@ -19,7 +19,26 @@ namespace Microsoft.Azure.Cosmos.Linq
     /// This class provides extension methods for cosmos LINQ code.
     /// </summary>
     public static class CosmosLinqExtensions
-    {
+    {
+        /// <summary>
+        /// Returns the integer identifier corresponding to a specific item within a physical partition.
+        /// This method is to be used in LINQ expressions only and will be evaluated on server.
+        /// There's no implementation provided in the client library.
+        /// </summary>
+        /// <param name="obj">The root object</param>
+        /// <returns>Returns the integer identifier corresponding to a specific item within a physical partition.</returns>
+        /// <example>
+        /// <code>
+        /// <![CDATA[
+        /// var documentIdQuery = documents.Where(root => root.DocumentId());
+        /// ]]>
+        /// </code>
+        /// </example>
+        public static int DocumentId(this object obj)
+        {
+            throw new NotImplementedException(ClientResources.TypeCheckExtensionFunctionsNotImplemented);
+        }
+
         /// <summary>
         /// Returns a Boolean value indicating if the type of the specified expression is an array.
         /// This method is to be used in LINQ expressions only and will be evaluated on server.

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

@@ -0,0 +1,50 @@
+<Results>
+  <Result>
+    <Input>
+      <Description><![CDATA[In Select clause]]></Description>
+      <Expression><![CDATA[query.Select(doc => doc.DocumentId())]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE DOCUMENTID(root) 
+FROM root]]></SqlQuery>
+    </Output>
+  </Result>
+  <Result>
+    <Input>
+      <Description><![CDATA[In Filter clause]]></Description>
+      <Expression><![CDATA[query.Where(doc => (doc.DocumentId() > 123))]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE root 
+FROM root 
+WHERE (DOCUMENTID(root) > 123)]]></SqlQuery>
+    </Output>
+  </Result>
+  <Result>
+    <Input>
+      <Description><![CDATA[With non root term]]></Description>
+      <Expression><![CDATA[query.Where(doc => (Convert(doc.BooleanField, Object).DocumentId() > 123))]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE root 
+FROM root 
+WHERE (DOCUMENTID(root["BooleanField"]) > 123)]]></SqlQuery>
+    </Output>
+  </Result>
+  <Result>
+    <Input>
+      <Description><![CDATA[In Order by clause]]></Description>
+      <Expression><![CDATA[query.OrderBy(doc => doc.DocumentId())]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE root 
+FROM root 
+ORDER BY DOCUMENTID(root) 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>
+  </Result>
+</Results>

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

@@ -290,6 +290,28 @@ public void TestTypeCheckFunctions()
             };
             this.ExecuteTestSuite(inputs);
         }
+
+        [TestMethod]
+        public void TestDocumentIdBuiltinFunction()
+        {
+            List<DataObject> data = new List<DataObject>();
+            IOrderedQueryable<DataObject> query = testContainer.GetItemLinqQueryable<DataObject>(allowSynchronousQueryExecution: true);
+            Func<bool, IQueryable<DataObject>> getQuery = useQuery => useQuery ? query : data.AsQueryable();
+
+            List<LinqTestInput> inputs = new List<LinqTestInput>
+            {
+                new LinqTestInput("In Select clause", b => getQuery(b).Select(doc => doc.DocumentId())),
+                new LinqTestInput("In Filter clause", b => getQuery(b).Where(doc => doc.DocumentId() > 123)),
+                new LinqTestInput("With non root term", b => getQuery(b).Where(doc => doc.BooleanField.DocumentId() > 123)),
+                new LinqTestInput("With JOIN", b => getQuery(b).SelectMany(doc => doc.EnumerableField
+                    .Where(number => doc.DocumentId() > 0)
+                    .Select(number => number))),
+                // Negative case
+                new LinqTestInput("In Order by clause", b => getQuery(b).OrderBy(doc => doc.DocumentId())),
+            };
+
+            this.ExecuteTestSuite(inputs);
+        }
 
         [TestMethod]
         public void TestRegexMatchFunction()

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/Contracts/DotNetSDKAPI.json

@@ -5650,6 +5650,13 @@
           ],
           "MethodInfo": "Boolean RegexMatch(System.Object, System.String);IsAbstract:False;IsStatic:True;IsVirtual:False;IsGenericMethod:False;IsConstructor:False;IsFinal:False;"
         },
+        "Int32 DocumentId(System.Object)[System.Runtime.CompilerServices.ExtensionAttribute()]": {
+          "Type": "Method",
+          "Attributes": [
+            "ExtensionAttribute"
+          ],
+          "MethodInfo": "Int32 DocumentId(System.Object);IsAbstract:False;IsStatic:True;IsVirtual:False;IsGenericMethod:False;IsConstructor:False;IsFinal:False;"
+        },
         "Microsoft.Azure.Cosmos.FeedIterator ToStreamIterator[T](System.Linq.IQueryable`1[T])[System.Runtime.CompilerServices.ExtensionAttribute()]": {
           "Type": "Method",
           "Attributes": [