Fix to #21006 - Support a default value for non-nullable properties

src/EFCore.Cosmos/Query/Internal/CosmosShapedQueryCompilingExpressionVisitor.CosmosProjectionBindingRemovingExpressionVisitorBase.cs

@@ -691,7 +691,11 @@ private Expression CreateGetValueExpression(
                 && !property.IsShadowProperty())
             {
                 var readExpression = CreateGetValueExpression(
-                    jTokenExpression, storeName, type.MakeNullable(), property.GetTypeMapping());
+                    jTokenExpression,
+                    storeName,
+                    type.MakeNullable(),
+                    property.GetTypeMapping(),
+                    isNonNullableScalar: false);
 
                 var nonNullReadExpression = readExpression;
                 if (nonNullReadExpression.Type != type)
@@ -712,15 +716,23 @@ private Expression CreateGetValueExpression(
             }
 
             return Convert(
-                CreateGetValueExpression(jTokenExpression, storeName, type.MakeNullable(), property.GetTypeMapping()),
+                CreateGetValueExpression(
+                    jTokenExpression,
+                    storeName,
+                    type.MakeNullable(),
+                    property.GetTypeMapping(),
+                    // special case keys - we check them for null to see if the entity needs to be materialized, so we want to keep the null, rather than non-nullable default
+                    // returning defaults is supposed to help with evolving the schema - so this doesn't concern keys anyway (they shouldn't evolve)
+                    isNonNullableScalar: !property.IsNullable && !property.IsKey()),
                 type);
         }
 
         private Expression CreateGetValueExpression(
             Expression jTokenExpression,
             string storeName,
             Type type,
-            CoreTypeMapping typeMapping = null)
+            CoreTypeMapping typeMapping = null,
+            bool isNonNullableScalar = false)
         {
             Check.DebugAssert(type.IsNullableType(), "Must read nullable type from JObject.");
 
@@ -763,6 +775,7 @@ var body
                             Constant(CosmosClientWrapper.Serializer)),
                         converter.ConvertFromProviderExpression.Body);
 
+                var originalBodyType = body.Type;
                 if (body.Type != type)
                 {
                     body = Convert(body, type);
@@ -783,7 +796,11 @@ var body
                 }
                 else
                 {
-                    replaceExpression = Default(type);
+                    replaceExpression = isNonNullableScalar
+                        ? Expression.Convert(
+                            Default(originalBodyType),
+                            type)
+                        : Default(type);
                 }
 
                 body = Condition(
@@ -799,7 +816,11 @@ var body
             }
             else
             {
-                valueExpression = ConvertJTokenToType(jTokenExpression, typeMapping?.ClrType.MakeNullable() ?? type);
+                valueExpression = ConvertJTokenToType(
+                    jTokenExpression,
+                    (isNonNullableScalar
+                        ? typeMapping?.ClrType
+                        : typeMapping?.ClrType.MakeNullable()) ?? type);
 
                 if (valueExpression.Type != type)
                 {

test/EFCore.Cosmos.FunctionalTests/Query/AdHocCosmosTestHelpers.cs

@@ -0,0 +1,43 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Net;
+using Microsoft.Azure.Cosmos;
+using Microsoft.EntityFrameworkCore.Cosmos.Storage.Internal;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.EntityFrameworkCore.Query;
+
+public class AdHocCosmosTestHelpers
+{
+    public static async Task CreateCustomEntityHelperAsync(
+        Container container,
+        string json,
+        CancellationToken cancellationToken)
+    {
+        var document = JObject.Parse(json);
+
+        var stream = new MemoryStream();
+        await using var __ = stream.ConfigureAwait(false);
+        var writer = new StreamWriter(stream, new UTF8Encoding(), bufferSize: 1024, leaveOpen: false);
+        await using var ___ = writer.ConfigureAwait(false);
+        using var jsonWriter = new JsonTextWriter(writer);
+
+        CosmosClientWrapper.Serializer.Serialize(jsonWriter, document);
+        await jsonWriter.FlushAsync(cancellationToken).ConfigureAwait(false);
+
+        var response = await container.CreateItemStreamAsync(
+                stream,
+                PartitionKey.None,
+                requestOptions: null,
+                cancellationToken)
+            .ConfigureAwait(false);
+
+
+        if (response.StatusCode != HttpStatusCode.Created)
+        {
+            throw new InvalidOperationException($"Failed to create entity (status code: {response.StatusCode}) for json: {json}");
+        }
+    }
+}