Fix sparse fields with DefaultEntityRepository.Get() override

src/JsonApiDotNetCore/Data/DefaultEntityRepository.cs

@@ -79,12 +79,15 @@ public DefaultEntityRepository(
         }
 
         /// <inheritdoc />
-        public virtual IQueryable<TEntity> Get()
+        public virtual IQueryable<TEntity> Get() 
+            => _dbSet;
+
+        public virtual IQueryable<TEntity> Select(IQueryable<TEntity> entities, List<string> fields)
         {
-            if (_jsonApiContext.QuerySet?.Fields != null && _jsonApiContext.QuerySet.Fields.Count > 0)
-                return _dbSet.Select(_jsonApiContext.QuerySet?.Fields);
+            if (fields?.Count > 0)
+                return entities.Select(fields);
 
-            return _dbSet;
+            return entities;
         }
 
         /// <inheritdoc />

src/JsonApiDotNetCore/Data/IEntityReadRepository.cs

@@ -20,6 +20,11 @@ public interface IEntityReadRepository<TEntity, in TId>
         /// </summary>
         IQueryable<TEntity> Get();
 
+        /// <summary>
+        /// Apply fields to the provided queryable
+        /// </summary>
+        IQueryable<TEntity> Select(IQueryable<TEntity> entities,List<string> fields);
+
         /// <summary>
         /// Include a relationship in the query
         /// </summary>

src/JsonApiDotNetCore/Services/EntityResourceService.cs

@@ -108,6 +108,9 @@ public virtual async Task<IEnumerable<TResource>> GetAsync()
             if (_jsonApiContext.Options.IncludeTotalRecordCount)
                 _jsonApiContext.PageManager.TotalRecords = await _entities.CountAsync(entities);
 
+            if (_jsonApiContext.QuerySet?.Fields?.Count > 0)
+                entities = _entities.Select(entities, _jsonApiContext.QuerySet.Fields);
+
             // pagination should be done last since it will execute the query
             var pagedEntities = await ApplyPageQueryAsync(entities);
             return pagedEntities;

test/JsonApiDotNetCoreExampleTests/Acceptance/Extensibility/RepositoryOverrideTests.cs

@@ -61,5 +61,42 @@ public async Task Total_Record_Count_Included()
             foreach(var item in deserializedBody)
                 Assert.Equal(person.Id, item.OwnerId);
         }
+
+        [Fact]
+        public async Task Sparse_Fields_Works_With_Get_Override()
+        {
+            // arrange
+            var builder = new WebHostBuilder()
+                .UseStartup<AuthorizedStartup>();
+            var server = new TestServer(builder);
+            var client = server.CreateClient();
+            var context = (AppDbContext)server.Host.Services.GetService(typeof(AppDbContext));
+            var jsonApiContext = (IJsonApiContext)server.Host.Services.GetService(typeof(IJsonApiContext));
+
+            var person = new Person();
+            context.People.Add(person);
+            var todoItem = new TodoItem();
+            todoItem.Owner = person;
+            context.TodoItems.Add(todoItem);
+            context.SaveChanges();
+
+            var authService = (IAuthorizationService)server.Host.Services.GetService(typeof(IAuthorizationService));
+            authService.CurrentUserId = person.Id;
+
+            var httpMethod = new HttpMethod("GET");
+            var route = $"/api/v1/todo-items/{todoItem.Id}?fields[todo-items]=description";
+
+            var request = new HttpRequestMessage(httpMethod, route);
+
+            // act
+            var response = await client.SendAsync(request);
+            var responseBody = await response.Content.ReadAsStringAsync();
+            var deserializedBody = _fixture.GetService<IJsonApiDeSerializer>().Deserialize<TodoItem>(responseBody);
+
+            // assert
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            Assert.Equal(todoItem.Description, deserializedBody.Description);
+
+        }
     }
 }