Fix/#354: Null reference exception when fetching relationships with compound name

src/JsonApiDotNetCore/Data/DefaultEntityRepository.cs

@@ -48,6 +48,7 @@ public DefaultEntityRepository(
             _genericProcessorFactory = _jsonApiContext.GenericProcessorFactory;
         }
 
+        /// </ inheritdoc>
         public virtual IQueryable<TEntity> Get()
         {
             if (_jsonApiContext.QuerySet?.Fields != null && _jsonApiContext.QuerySet.Fields.Count > 0)
@@ -56,21 +57,25 @@ public virtual IQueryable<TEntity> Get()
             return _dbSet;
         }
 
+        /// </ inheritdoc>
         public virtual IQueryable<TEntity> Filter(IQueryable<TEntity> entities, FilterQuery filterQuery)
         {
             return entities.Filter(_jsonApiContext, filterQuery);
         }
 
+        /// </ inheritdoc>
         public virtual IQueryable<TEntity> Sort(IQueryable<TEntity> entities, List<SortQuery> sortQueries)
         {
             return entities.Sort(sortQueries);
         }
 
+        /// </ inheritdoc>
         public virtual async Task<TEntity> GetAsync(TId id)
         {
             return await Get().SingleOrDefaultAsync(e => e.Id.Equals(id));
         }
 
+        /// </ inheritdoc>
         public virtual async Task<TEntity> GetAndIncludeAsync(TId id, string relationshipName)
         {
             _logger.LogDebug($"[JADN] GetAndIncludeAsync({id}, {relationshipName})");
@@ -80,6 +85,7 @@ public virtual async Task<TEntity> GetAndIncludeAsync(TId id, string relationshi
             return result;
         }
 
+        /// </ inheritdoc>
         public virtual async Task<TEntity> CreateAsync(TEntity entity)
         {
             AttachRelationships();
@@ -102,9 +108,9 @@ protected virtual void AttachRelationships()
         private void AttachHasManyPointers()
         {
             var relationships = _jsonApiContext.HasManyRelationshipPointers.Get();
-            foreach(var relationship in relationships)
+            foreach (var relationship in relationships)
             {
-                foreach(var pointer in relationship.Value)
+                foreach (var pointer in relationship.Value)
                 {
                     _context.Entry(pointer).State = EntityState.Unchanged;
                 }
@@ -123,6 +129,7 @@ private void AttachHasOnePointers()
                     _context.Entry(relationship.Value).State = EntityState.Unchanged;
         }
 
+        /// </ inheritdoc>
         public virtual async Task<TEntity> UpdateAsync(TId id, TEntity entity)
         {
             var oldEntity = await GetAsync(id);
@@ -141,12 +148,14 @@ public virtual async Task<TEntity> UpdateAsync(TId id, TEntity entity)
             return oldEntity;
         }
 
+        /// </ inheritdoc>
         public async Task UpdateRelationshipsAsync(object parent, RelationshipAttribute relationship, IEnumerable<string> relationshipIds)
         {
             var genericProcessor = _genericProcessorFactory.GetProcessor<IGenericProcessor>(typeof(GenericProcessor<>), relationship.Type);
             await genericProcessor.UpdateRelationshipsAsync(parent, relationship, relationshipIds);
         }
 
+        /// </ inheritdoc>
         public virtual async Task<bool> DeleteAsync(TId id)
         {
             var entity = await GetAsync(id);
@@ -161,11 +170,12 @@ public virtual async Task<bool> DeleteAsync(TId id)
             return true;
         }
 
+        /// </ inheritdoc>
         public virtual IQueryable<TEntity> Include(IQueryable<TEntity> entities, string relationshipName)
         {
             var entity = _jsonApiContext.RequestEntity;
             var relationship = entity.Relationships.FirstOrDefault(r => r.PublicRelationshipName == relationshipName);
-            if (relationship == null) 
+            if (relationship == null)
             {
                 throw new JsonApiException(400, $"Invalid relationship {relationshipName} on {entity.EntityName}",
                     $"{entity.EntityName} does not have a relationship named {relationshipName}");
@@ -178,6 +188,7 @@ public virtual IQueryable<TEntity> Include(IQueryable<TEntity> entities, string
             return entities.Include(relationship.InternalRelationshipName);
         }
 
+        /// </ inheritdoc>
         public virtual async Task<IEnumerable<TEntity>> PageAsync(IQueryable<TEntity> entities, int pageSize, int pageNumber)
         {
             if (pageNumber >= 0)
@@ -198,20 +209,23 @@ public virtual async Task<IEnumerable<TEntity>> PageAsync(IQueryable<TEntity> en
                     .ToListAsync();
         }
 
+        /// </ inheritdoc>
         public async Task<int> CountAsync(IQueryable<TEntity> entities)
         {
             return (entities is IAsyncEnumerable<TEntity>)
                  ? await entities.CountAsync()
                  : entities.Count();
         }
 
+        /// </ inheritdoc>
         public async Task<TEntity> FirstOrDefaultAsync(IQueryable<TEntity> entities)
         {
             return (entities is IAsyncEnumerable<TEntity>)
                ? await entities.FirstOrDefaultAsync()
                : entities.FirstOrDefault();
         }
 
+        /// </ inheritdoc>
         public async Task<IReadOnlyList<TEntity>> ToListAsync(IQueryable<TEntity> entities)
         {
             return (entities is IAsyncEnumerable<TEntity>)

src/JsonApiDotNetCore/Data/IEntityReadRepository.cs

@@ -6,32 +6,75 @@
 
 namespace JsonApiDotNetCore.Data
 {
-     public interface IEntityReadRepository<TEntity>
-        : IEntityReadRepository<TEntity, int>
-        where TEntity : class, IIdentifiable<int>
+    public interface IEntityReadRepository<TEntity>
+       : IEntityReadRepository<TEntity, int>
+       where TEntity : class, IIdentifiable<int>
     { }
 
     public interface IEntityReadRepository<TEntity, in TId>
         where TEntity : class, IIdentifiable<TId>
     {
+        /// <summary>
+        /// The base GET query. This is a good place to apply rules that should affect all reads, 
+        /// such as authorization of resources.
+        /// </summary>
         IQueryable<TEntity> Get();
 
+        /// <summary>
+        /// Include a relationship in the query
+        /// </summary>
+        /// <example>
+        /// <code>
+        /// _todoItemsRepository.GetAndIncludeAsync(1, "achieved-date");
+        /// </code>
+        /// </example>
         IQueryable<TEntity> Include(IQueryable<TEntity> entities, string relationshipName);
 
+        /// <summary>
+        /// Apply a filter to the provided queryable
+        /// </summary>
         IQueryable<TEntity> Filter(IQueryable<TEntity> entities, FilterQuery filterQuery);
 
+        /// <summary>
+        /// Apply a sort to the provided queryable
+        /// </summary>
         IQueryable<TEntity> Sort(IQueryable<TEntity> entities, List<SortQuery> sortQueries);
 
+        /// <summary>
+        /// Paginate the provided queryable
+        /// </summary>
         Task<IEnumerable<TEntity>> PageAsync(IQueryable<TEntity> entities, int pageSize, int pageNumber);
 
+        /// <summary>
+        /// Get the entity by id
+        /// </summary>
         Task<TEntity> GetAsync(TId id);
 
+        /// <summary>
+        /// Get the entity with the specified id and include the relationship.
+        /// </summary>
+        /// <param name="id">The entity id</param>
+        /// <param name="relationshipName">The exposed relationship name</param>
+        /// <example>
+        /// <code>
+        /// _todoItemsRepository.GetAndIncludeAsync(1, "achieved-date");
+        /// </code>
+        /// </example>
         Task<TEntity> GetAndIncludeAsync(TId id, string relationshipName);
 
+        /// <summary>
+        /// Count the total number of records
+        /// </summary>
         Task<int> CountAsync(IQueryable<TEntity> entities);
 
+        /// <summary>
+        /// Get the first element in the collection, return the default value if collection is empty
+        /// </summary>
         Task<TEntity> FirstOrDefaultAsync(IQueryable<TEntity> entities);
 
+        /// <summary>
+        /// Convert the collection to a materialized list
+        /// </summary>
         Task<IReadOnlyList<TEntity>> ToListAsync(IQueryable<TEntity> entities);
     }
 }

src/JsonApiDotNetCore/Internal/ContextGraph.cs

@@ -6,10 +6,45 @@ namespace JsonApiDotNetCore.Internal
 {
     public interface IContextGraph
     {
-        object GetRelationship<TParent>(TParent entity, string relationshipName);
+        /// <summary>
+        /// Gets the value of the navigation property, defined by the relationshipName, 
+        /// on the provided instance.
+        /// </summary>
+        /// <param name="resource">The resource instance</param>
+        /// <param name="propertyName">The navigation property name.</param>
+        /// <example>
+        /// <code>
+        /// _graph.GetRelationship(todoItem, nameof(TodoItem.Owner));
+        /// </code>
+        /// </example>
+        object GetRelationship<TParent>(TParent resource, string propertyName);
+
+        /// <summary>
+        /// Get the internal navigation property name for the specified public
+        /// relationship name.
+        /// </summary>
+        /// <param name="relationshipName">The public relationship name specified by a <see cref="HasOneAttribute" /> or <see cref="HasManyAttribute" /></param>
+        /// <example>
+        /// <code>
+        /// _graph.GetRelationshipName&lt;TodoItem&gt;("achieved-date");
+        /// // returns "AchievedDate"
+        /// </code>
+        /// </example>
         string GetRelationshipName<TParent>(string relationshipName);
+
+        /// <summary>
+        /// Get the resource metadata by the DbSet property name
+        /// </summary>
         ContextEntity GetContextEntity(string dbSetName);
+
+        /// <summary>
+        /// Get the resource metadata by the resource type
+        /// </summary>
         ContextEntity GetContextEntity(Type entityType);
+
+        /// <summary>
+        /// Was built against an EntityFrameworkCore DbContext ?
+        /// </summary>
         bool UsesDbContext { get; }
     }
 
@@ -40,14 +75,18 @@ internal ContextGraph(List<ContextEntity> entities, bool usesDbContext, List<Val
             Instance = this;
         }
 
+        /// </ inheritdoc>
         public bool UsesDbContext { get; }
 
+        /// </ inheritdoc>
         public ContextEntity GetContextEntity(string entityName)
             => Entities.SingleOrDefault(e => string.Equals(e.EntityName, entityName, StringComparison.OrdinalIgnoreCase));
 
+        /// </ inheritdoc>
         public ContextEntity GetContextEntity(Type entityType)
             => Entities.SingleOrDefault(e => e.EntityType == entityType);
 
+        /// </ inheritdoc>
         public object GetRelationship<TParent>(TParent entity, string relationshipName)
         {
             var parentEntityType = entity.GetType();
@@ -62,6 +101,7 @@ public object GetRelationship<TParent>(TParent entity, string relationshipName)
             return navigationProperty.GetValue(entity);
         }
 
+        /// </ inheritdoc>
         public string GetRelationshipName<TParent>(string relationshipName)
         {
             var entityType = typeof(TParent);