Cosmos: Stop nesting results in extra JSON object

Closes #25527

src/EFCore.Cosmos/Extensions/Internal/CosmosShapedQueryExpressionExtensions.cs

@@ -214,7 +214,6 @@ public static bool TryExtractArray(
                             Limit: null,
                             Orderings: [],
                             IsDistinct: false,
-                            UsesSingleValueProjection: true,
                             Projection: [{ Expression: var a }]
                         },
                     }

src/EFCore.Cosmos/Query/Internal/CosmosQuerySqlGenerator.cs

@@ -281,8 +281,7 @@ protected override Expression VisitSelect(SelectExpression selectExpression)
         {
             // If the SELECT projects a single value out, we just project that with the Cosmos VALUE keyword (without VALUE,
             // Cosmos projects a JSON object containing the value).
-            // TODO: Ideally, just always use VALUE for all single-projection SELECTs - but this like requires shaper changes.
-            if (selectExpression.UsesSingleValueProjection && projection is [var singleProjection])
+            if (projection is [var singleProjection])
             {
                 _sqlBuilder.Append("VALUE ");
 
@@ -752,7 +751,6 @@ void VisitContainerExpression(Expression containerExpression)
                 Limit: null,
                 Orderings: [],
                 IsDistinct: false,
-                UsesSingleValueProjection: true,
                 Projection.Count: 1
             };
 

src/EFCore.Cosmos/Query/Internal/Expressions/ObjectReferenceExpression.cs

@@ -14,7 +14,7 @@ namespace Microsoft.EntityFrameworkCore.Cosmos.Query.Internal;
 ///     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.
 /// </remarks>
-public class ObjectReferenceExpression(IEntityType entityType, string name) : Expression, IAccessExpression
+public class ObjectReferenceExpression(IEntityType entityType, string name) : Expression, IPrintableExpression, IAccessExpression
 {
     /// <summary>
     ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
@@ -72,6 +72,15 @@ string IAccessExpression.PropertyName
     protected override Expression VisitChildren(ExpressionVisitor visitor)
         => this;
 
+    /// <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>
+    public void Print(ExpressionPrinter expressionPrinter)
+        => expressionPrinter.Append(Name);
+
     /// <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

src/EFCore.Cosmos/Query/Internal/Expressions/ProjectionExpression.cs

@@ -10,6 +10,7 @@ namespace Microsoft.EntityFrameworkCore.Cosmos.Query.Internal;
 ///     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>
+[DebuggerDisplay("{Microsoft.EntityFrameworkCore.Query.ExpressionPrinter.Print(this), nq}")]
 public class ProjectionExpression(Expression expression, string alias)
     : Expression, IPrintableExpression
 {

src/EFCore.Cosmos/Query/Internal/Expressions/SelectExpression.cs

@@ -89,18 +89,12 @@ public static SelectExpression CreateForCollection(Expression sourceExpression,
             sourceExpression = new SelectExpression(
                 [new ProjectionExpression(sourceExpression, null!)],
                 sources: [],
-                orderings: [])
-            {
-                UsesSingleValueProjection = true
-            };
+                orderings: []);
         }
 
         var source = new SourceExpression(sourceExpression, sourceAlias, withIn: true);
 
-        return new SelectExpression(source, projection)
-        {
-            UsesSingleValueProjection = true
-        };
+        return new SelectExpression(source, projection);
     }
 
     /// <summary>
@@ -112,18 +106,6 @@ [new ProjectionExpression(sourceExpression, null!)],
     public IReadOnlyList<ProjectionExpression> Projection
         => _projection;
 
-    /// <summary>
-    ///     If set, indicates that the <see cref="SelectExpression" /> has a Cosmos VALUE projection, which does not get wrapped in a
-    ///     JSON object. If <see langword="true" />, <see cref="Projection" /> must contain a single item.
-    /// </summary>
-    /// <remarks>
-    ///     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.
-    /// </remarks>
-    public bool UsesSingleValueProjection { get; init; }
-
     /// <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
@@ -595,8 +577,7 @@ protected override Expression VisitChildren(ExpressionVisitor visitor)
                 Predicate = predicate,
                 Offset = offset,
                 Limit = limit,
-                IsDistinct = IsDistinct,
-                UsesSingleValueProjection = UsesSingleValueProjection
+                IsDistinct = IsDistinct
             };
 
             return newSelectExpression;
@@ -632,7 +613,6 @@ public SelectExpression Update(
             Offset = offset,
             Limit = limit,
             IsDistinct = IsDistinct,
-            UsesSingleValueProjection = UsesSingleValueProjection,
             ReadItemInfo = ReadItemInfo
         };
     }
@@ -658,7 +638,6 @@ public SelectExpression WithSingleValueProjection()
             Offset = Offset,
             Limit = Limit,
             IsDistinct = IsDistinct,
-            UsesSingleValueProjection = true
         };
     }
 
@@ -711,18 +690,18 @@ private void PrintSql(ExpressionPrinter expressionPrinter, bool withTags = true)
             expressionPrinter.Append("DISTINCT ");
         }
 
-        if (Projection.Any())
+        switch (Projection)
         {
-            if (UsesSingleValueProjection)
-            {
+            case []:
+                expressionPrinter.Append("1");
+                break;
+            case [var singleProjection]:
                 expressionPrinter.Append("VALUE ");
-            }
-
-            expressionPrinter.VisitCollection(Projection);
-        }
-        else
-        {
-            expressionPrinter.Append("1");
+                expressionPrinter.Visit(singleProjection);
+                break;
+            default:
+                expressionPrinter.VisitCollection(Projection);
+                break;
         }
 
         if (Sources.Count > 0)