Json Columns query work

- property/navigation access translation,
- materialization (entity, collection, with nesting),
- null semantics,

+ tweaks and fixes to the metadata/update part

src/EFCore.Relational/Extensions/RelationalEntityTypeExtensions.cs

@@ -1758,10 +1758,10 @@ public static void SetJsonPropertyName(this IMutableEntityType entityType, strin
             Check.NullButNotEmpty(name, nameof(name)));
 
     /// <summary>
-    ///     Gets the <see cref="ConfigurationSource" /> for the JSON property name for a given entity Type.
+    ///     Gets the <see cref="ConfigurationSource" /> for the JSON property name for a given entity type.
     /// </summary>
     /// <param name="entityType">The entity type.</param>
-    /// <returns>The <see cref="ConfigurationSource" /> for the JSON property name for a given navigation.</returns>
+    /// <returns>The <see cref="ConfigurationSource" /> for the JSON property name for a given entity type.</returns>
     public static ConfigurationSource? GetJsonPropertyNameConfigurationSource(this IConventionEntityType entityType)
         => entityType.FindAnnotation(RelationalAnnotationNames.JsonPropertyName)?.GetConfigurationSource();
 

src/EFCore.Relational/Metadata/Internal/RelationalKeyExtensions.cs

@@ -124,6 +124,11 @@ public static bool AreCompatible(
             return null;
         }
 
+        if (key.DeclaringEntityType.IsMappedToJson())
+        {
+            return null;
+        }
+
         string? name;
         if (key.IsPrimaryKey())
         {

src/EFCore.Relational/Metadata/Internal/RelationalModel.cs

@@ -468,7 +468,7 @@ private static void CreateTableMapping(
                 var jsonColumnTypeMapping = relationalTypeMappingSource.FindMapping(typeof(JsonElement))!;
                 var jsonColumn = new JsonColumn(containerColumnName, jsonColumnTypeMapping.StoreType, table, jsonColumnTypeMapping.ProviderValueComparer);
                 table.Columns.Add(containerColumnName, jsonColumn);
-                jsonColumn.IsNullable = !ownership.IsRequired || !ownership.IsUnique;
+                jsonColumn.IsNullable = !ownership.IsRequiredDependent || !ownership.IsUnique;
 
                 if (ownership.PrincipalEntityType.BaseType != null)
                 {

src/EFCore.Relational/Properties/RelationalStrings.resx

@@ -481,6 +481,9 @@
   <data name="InvalidPropertyInSetProperty" xml:space="preserve">
     <value>The following lambda argument to 'SetProperty' does not represent a valid property to be set: '{propertyExpression}'.</value>
   </data>
+  <data name="JsonCantNavigateToParentEntity" xml:space="preserve">
+    <value>Can't navigate from JSON-mapped entity '{jsonEntity}' to its parent entity '{parentEntity}' using navigation '{navigation}'. Entities mapped to JSON can only navigate to their children.</value>
+  </data>
   <data name="JsonEntityMappedToDifferentViewThanOwner" xml:space="preserve">
     <value>Entity '{jsonType}' is mapped to JSON and also to a view '{viewName}', but its owner '{ownerType}' is mapped to a different view '{ownerViewName}'. Every entity mapped to JSON must also map to the same view as its owner.</value>
   </data>
@@ -517,9 +520,18 @@
   <data name="JsonEntityWithTableSplittingIsNotSupported" xml:space="preserve">
     <value>Table splitting is not supported for entities containing entities mapped to JSON.</value>
   </data>
+  <data name="JsonErrorExtractingJsonProperty" xml:space="preserve">
+    <value>An error occurred while reading a JSON value for property '{entityType}.{propertyName}'. See the inner exception for more information.</value>
+  </data>
+  <data name="JsonNodeMustBeHandledByProviderSpecificVisitor" xml:space="preserve">
+    <value>This node should be handled by provider-specific sql generator.</value>
+  </data>
   <data name="JsonPropertyNameShouldBeConfiguredOnNestedNavigation" xml:space="preserve">
     <value>The JSON property name should only be configured on nested owned navigations.</value>
   </data>
+  <data name="JsonRequiredEntityWithNullJson" xml:space="preserve">
+    <value>Entity {entity} is required but the JSON element containing it is null.</value>
+  </data>
   <data name="KeylessMappingStrategy" xml:space="preserve">
     <value>The mapping strategy '{mappingStrategy}' used for '{entityType}' is not supported for keyless entity types.  See https://go.microsoft.com/fwlink/?linkid=2130430 for more information.</value>
   </data>

src/EFCore.Relational/Query/EntityProjectionExpression.cs

@@ -17,7 +17,7 @@ namespace Microsoft.EntityFrameworkCore.Query;
 public class EntityProjectionExpression : Expression
 {
     private readonly IReadOnlyDictionary<IProperty, ColumnExpression> _propertyExpressionMap;
-    private readonly Dictionary<INavigation, EntityShaperExpression> _ownedNavigationMap = new();
+    private readonly Dictionary<INavigation, EntityShaperExpression> _ownedNavigationMap;
 
     /// <summary>
     ///     Creates a new instance of the <see cref="EntityProjectionExpression" /> class.
@@ -29,9 +29,23 @@ public EntityProjectionExpression(
         IEntityType entityType,
         IReadOnlyDictionary<IProperty, ColumnExpression> propertyExpressionMap,
         SqlExpression? discriminatorExpression = null)
+        : this(
+            entityType,
+            propertyExpressionMap,
+            new Dictionary<INavigation, EntityShaperExpression>(),
+            discriminatorExpression)
+    {
+    }
+
+    private EntityProjectionExpression(
+        IEntityType entityType,
+        IReadOnlyDictionary<IProperty, ColumnExpression> propertyExpressionMap,
+        Dictionary<INavigation, EntityShaperExpression> ownedNavigationMap,
+        SqlExpression? discriminatorExpression = null)
     {
         EntityType = entityType;
         _propertyExpressionMap = propertyExpressionMap;
+        _ownedNavigationMap = ownedNavigationMap;
         DiscriminatorExpression = discriminatorExpression;
     }
 
@@ -69,8 +83,16 @@ protected override Expression VisitChildren(ExpressionVisitor visitor)
         var discriminatorExpression = (SqlExpression?)visitor.Visit(DiscriminatorExpression);
         changed |= discriminatorExpression != DiscriminatorExpression;
 
+        var ownedNavigationMap = new Dictionary<INavigation, EntityShaperExpression>();
+        foreach (var (navigation, entityShaperExpression) in _ownedNavigationMap)
+        {
+            var newExpression = (EntityShaperExpression)visitor.Visit(entityShaperExpression);
+            changed |= newExpression != entityShaperExpression;
+            ownedNavigationMap[navigation] = newExpression;
+        }
+
         return changed
-            ? new EntityProjectionExpression(EntityType, propertyExpressionMap, discriminatorExpression)
+            ? new EntityProjectionExpression(EntityType, propertyExpressionMap, ownedNavigationMap, discriminatorExpression)
             : this;
     }
 
@@ -92,7 +114,65 @@ public virtual EntityProjectionExpression MakeNullable()
             // if discriminator is column then we need to make it nullable
             discriminatorExpression = ce.MakeNullable();
         }
-        return new EntityProjectionExpression(EntityType, propertyExpressionMap, discriminatorExpression);
+
+        var primaryKeyProperties = GetMappedKeyProperties(EntityType.FindPrimaryKey()!);
+        var ownedNavigationMap = new Dictionary<INavigation, EntityShaperExpression>();
+        foreach (var (navigation, shaper) in _ownedNavigationMap)
+        {
+            if (shaper.EntityType.IsMappedToJson())
+            {
+                // even if shaper is nullable, we need to make sure key property map contains nullable keys,
+                // if json entity itself is optional, the shaper would be null, but the PK of the owner entity would be non-nullable intially
+                Debug.Assert(primaryKeyProperties != null, "Json entity type can't be keyless");
+
+                var jsonQueryExpression = (JsonQueryExpression)shaper.ValueBufferExpression;
+                var ownedPrimaryKeyProperties = GetMappedKeyProperties(shaper.EntityType.FindPrimaryKey()!)!;
+                var nullableKeyPropertyMap = new Dictionary<IProperty, ColumnExpression>();
+                for (var i = 0; i < primaryKeyProperties.Count; i++)
+                {
+                    nullableKeyPropertyMap[ownedPrimaryKeyProperties[i]] = propertyExpressionMap[primaryKeyProperties[i]];
+                }
+
+                // reuse key columns from owner (that we just made nullable), so that the references are the same
+                var newJsonQueryExpression = jsonQueryExpression.MakeNullable(nullableKeyPropertyMap);
+                var newShaper = shaper.Update(newJsonQueryExpression).MakeNullable();
+                ownedNavigationMap[navigation] = newShaper;
+            }
+        }
+
+        return new EntityProjectionExpression(
+            EntityType,
+            propertyExpressionMap,
+            ownedNavigationMap,
+            discriminatorExpression);
+
+        static IReadOnlyList<IProperty>? GetMappedKeyProperties(IKey? key)
+        {
+            if (key == null)
+            {
+                return null;
+            }
+
+            if (!key.DeclaringEntityType.IsMappedToJson())
+            {
+                return key.Properties;
+            }
+
+            // TODO: fix this once we enable json entity being owned by another owned non-json entity (issue #28441)
+
+            // for json collections we need to filter out the ordinal key as it's not mapped to any column
+            // there could be multiple of these in deeply nested structures,
+            // so we traverse to the outermost owner to see how many mapped keys there are
+            var currentEntity = key.DeclaringEntityType;
+            while (currentEntity.IsMappedToJson())
+            {
+                currentEntity = currentEntity.FindOwnership()!.PrincipalEntityType;
+            }
+
+            var count = currentEntity.FindPrimaryKey()!.Properties.Count;
+
+            return key.Properties.Take(count).ToList();
+        }
     }
 
     /// <summary>
@@ -119,6 +199,16 @@ public virtual EntityProjectionExpression UpdateEntityType(IEntityType derivedTy
             }
         }
 
+        var ownedNavigationMap = new Dictionary<INavigation, EntityShaperExpression>();
+        foreach (var (navigation, entityShaperExpression) in _ownedNavigationMap)
+        {
+            if (derivedType.IsAssignableFrom(navigation.DeclaringEntityType)
+                || navigation.DeclaringEntityType.IsAssignableFrom(derivedType))
+            {
+                ownedNavigationMap[navigation] = entityShaperExpression;
+            }
+        }
+
         var discriminatorExpression = DiscriminatorExpression;
         if (DiscriminatorExpression is CaseExpression caseExpression)
         {
@@ -130,7 +220,7 @@ public virtual EntityProjectionExpression UpdateEntityType(IEntityType derivedTy
             discriminatorExpression = caseExpression.Update(operand: null, whenClauses, elseResult: null);
         }
 
-        return new EntityProjectionExpression(derivedType, propertyExpressionMap, discriminatorExpression);
+        return new EntityProjectionExpression(derivedType, propertyExpressionMap, ownedNavigationMap, discriminatorExpression);
     }
 
     /// <summary>