November 17, 2018

A1 Repo: Simple Pagination for WCF Service Operation

It is never a good idea to paginate on the client.  This post is about a simple pagination for a WCF service operation.  For this work I need a RequestModel and a ResponseModel.

The RequestModel contains two properties; PageNumber and PageSize.  The RequestModerl could contain sort order by certain fields but because this is simple pagination no sorting by fields is supported in this note.

The ResonseModel has a list of items of reference type T and other properties which could be used by the client.

The service in question has tree operations:

We are particularly interested in the implementation of  ResponseModel GetEmployeesByRequest(RequestModel request) and here it is:

The interesting part is the OrderBy > Skip > Take.  Note that in case that the client asks for a page which does not exist the actual page is reset to the last page so we know the records to skip. Note that what is sent to the client has been mapped to a specific DataContract and it was done using a mapping extension very similar to how it was done in A1 Repo: Explicit Mapping Using Extensions Methods Rather than Using AutoMapper.

This little POC is tested using a console application.  Note that when a service reference is created the  client proxy offers the possibility of using asynchronous programming.

For this note the Adventure2012 database was used.  The ORM employed was Entity Framework and the model was created using the Entity Data Model Wizard > Code First from Database.

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November 5, 2018

A1 Repo: Explicit Mapping Using Extensions Methods Rather than Using AutoMapper

There are many reasons not to use AutoMapper in projects. I started to use AutoMapper about five years ago and the first problem that I encountered from the start gate was that using Automapper creates mapping code which is very difficult, and at times impossible to debug. Another equally distressing observation is that the code can become very complex very quickly due to formatting and conditional mappings which need to be configured in the mapper configuration.

The only one thing that I liked about AutoMapper is that I can tack away the mapping code making service operations, controller actions and methods in general more readable. Hence, in the spirit of putting away the mapping code I prefer to do explicit mapping using extension methods.

The following snippet of code maps AssetDto to AssetViewModel.

Mapping the ViewModel to a Dto would be done just in the same fashion through extension methods.

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November 4, 2018

A1 Repro (ASP.Net CORE): Loading Lookup Collection in Action Filter and Simple Dropdownlist Editor

There are times when a collection of lookup to populate a drop down list is needed; this is very common. The usual solution is to create an Enumerable property in the view model to hold the lookup values, inject a service in the controller then in the action load the list to the view model and load the view. A complete example can be accessed at Pluralsight where dropdown lists are polulated in Razor views using the MVVM design pattern, Entity Framework, and Ajax.

Another approach is to load the lookup collection to the ViewData and access the values from the view or a template editor. This note is about a modification of this approach where the lookup collection is loaded into the ViewData using a Fiter Service which decorates the action requiring the loopkup collection.

The Filter
The following filter loads a collection of AssetTypes and converts the collection of DTOs into a SelectListItems using an extension method and loads the list on the ViewData.

The way to consume this filter service attribute is through the ServiceFilter, decorating the action with [ServiceFilter(typeof(AssetTypeCollectionAttribute))] this way:

Inject Service
Like any other service, the Filter Service needs to be injected in order to be discovered, therefore for an ASP.Net CORE application AssetTypeCollectionAttribute needs to  be injected.  In this example is added for the scope of the request:

Simple Drop Down List Editor
The editor template is simple, and can be reused for other lookup lists.

ViewModel and View
To end the note; the editor is invoked from the view passing two parameters in the ViewData; the index or key used to store the collection in the ViewData and the initial default message to load in the drop down list.

None of the above would work if the ViewModel does not have property AssetType decorated with [UIHint("ViewDropdown")]

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November 2, 2018

A1 Repo: Snippets to Save the Day!

I find myself reinventing the same wheel over and over again and wish I had my repository of my own creation handy. Well, for my own enjoyment I will write a series of articles containing snippets of code which can be reused anywhere. This is the motivation of the "A1 Repo" series and instead of reinventing myself, perhaps this articles will help me making my own creation better. I am not documenting the "other" way of doing things but the final chunk of code which is good for reusing.

Snippets Table of Content:

  1. ASP.Net MVC Editor Template Date using jQuery Date picker supporting Bootstrap 4
  2. Loading Lookup Collection in Action Filter and Simple Dropdownlist Editor (ASP.Net CORE)
  3. Explicit Mapping Using Extensions Methods Rather Using AutoMapper
  4. Simple Pagination for WCF Service Operation

A1 Repro: An Easy Date Editor Template suitable for jQuery Date Picker Plugin

This entry is about creating an editor template for an ASP.Net MVC solution for a Date.

The following piece of code shows a section of "PropertyViewModel" class containing three different dates; "TotalValueAssessmentDate", "PreviousYearValueAssessmentDate", and "LastInspected".

Only these three dates would generate a busy markup, hence to avoid that use an editor for the DateTime data type, which is hinted by the UIHint annotation on the property.

The view now is very easy to read as we see the editor usages right away. The template is also very simple.

The above editor is meant to be used with bootstrap-datepicker jQuery plugin. You can find the plugin documentation in the provided link reference.

The javascript spinet which loads the calendar popup looks like this:

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July 10, 2017

The Model Exists But The Database Is Empty: Unit Test With A Mocking Framework Is Best ROI

The Model Is Ready But No Data: Consider Mocking

I am sure you have encountered this scenario rather often especially in the early stages of a project: the model is present, the database was created but there is no test data. 

"Oooooo!  I’ll blast yall tables off with seed data varmints!"

If we are using Entity Framework Code-First then we could seed data during the database initialization process.  However, in the case that a DB initialization is not possible, the data could still be seeded following a different mechanism.  Assuming that I was working on a system based on the Northwind database, and the database was empty then data could be seeded and the process is very simple:

 public async Task SeedDataAsync()  
         var category = _context  
           .FirstOrDefault(c => c.CategoryName.Equals("Beverages"));  
         if(category == null)  
           category = new Category  
             CategoryName = "Beverages",  
             Description = "Soft drinks, coffees, teas, beers, and ales"  
         var supplier = new Supplier  
           CompanyName = "Joe's One Stop",  
           ContactName = "Joe Marino",  
           Address = "123 Main St.",  
           City = "Ottawa",  
           Region = "ON",  
           PostalCode = "O6T 3P9",  
           Country = "Canada",  
           Phone = "613-555-1232",  
           HomePage = "",  
           Products = new List<Product>  
             new Product() { ProductName = "Sasquatch Ale", QuantityPerUnit = "24 - 12 oz bottles", UnitPrice = 14.00m, UnitsInStock = 111, Category = category },  
             new Product() { ProductName = "Steeleye Stout", QuantityPerUnit = "24 - 12 oz bottles", UnitPrice = 18.00m, UnitsInStock = 20, Category = category },  
             new Product() { ProductName = "Laughing Lumberjack Lager", QuantityPerUnit = "24 - 12 oz bottles", UnitPrice = 13.50m, UnitsInStock = 52, Category = category }  
         if (category.CategoryID == 0 ) _context.Categories.Add(category);  
         await _context.SaveChangesAsync();  

then call it when the system initializes, or in a startup sequence like this:


I have not tested the above seed but it encapsulates the general idea.

Seeding data has its use and benefits because it allows to create a base data on which development can start and progress can be shown fairly quickly and the software development process shows advance.

However, there are scenarios where trying to seed data for the lack of it might be counterproductive and as a result we find ourselves losing perspective as to what the software we are building is trying to accomplish.  To seed the needed data we dedicate massive amounts of time with the hope to get our development moving forward; data that at the end of the day is thrown away.  Even when we have managed to seed data I have encountered scenarios where other developers have modified the data for one reason or another and now the feature under development or unit tests does not work anymore.

Mocking frameworks can help us abstract dependencies to a data access layer.  Using mocking frameworks we can create these mock object which can be setup to provide data needed to develop and test a feature and never access the database.

Using mock objects also allows unit tests to isolate themselves, hence, the feature under development can be tested carefully.

In my previous note, Testing EF 6.x Async Queries With Moq: In Memory DbAsyncQueryProvider using mock objects allowed testing Task<IQueryable<CustomerOrderStatistic>> CustomerOrderSummaryAsync(   CustomerOrderSearch criteria) without accessing the database because the data required for the method under test was provided by mocking repositories required by the service.  Hence the development of the feature was done in isolation.  Here are the tests that were designed and executed:

Moq framework used to mock DbSet and repositories


The take home message is that using mocking frameworks will force you to start developing a Unit Test infrastructure, and the benefits that we collect from such infrastructure are long lasting.  For instance:
  1. Mock objects helps greatly in a Test Driven Development process.  It takes time and practice to develop a TDD state of mind.  
  2. Test new features in isolation, helping test coverage.
  3. Abstract data access layer: the functionality can be tested without the need of seeded data.
  4. As a result of the above item; developing functionality which depends on the implementation of other dependencies can be undertaken because those dependencies can be mocked.  (mocking repositories, the above unit tests does not need the implementation of repositories dependencies only their definitions.
  5. As a result of conclusion 2 and 3; good SOLID Object Oriented principles become pivotal hence if dependencies are very hard to mock then the original design start to release its own smell.
This post is not trying to say that seed data to help us develop new features is a bad thing.  Seeding data has its own objectives and is a powerful tool at our disposal, however, we should not depend on seeded data to be able to develop new functionality :  mocking framework and TDD together are great tools to consider.

Testing EF 6.x Async Queries With Moq: In Memory DbAsyncQueryProvider


The objective of this post is to test an asynchronous service operation, and in particular methods which include Entity Framework 6.x asynchronous queries.  When conducting unit testing of asynchronous code my starting point had to be a post by Stephen Cleary.  This article introduces the reader to the subject. providing general guidelines, what to avoid, valuable insights, etc.  His blog is also a valuable resource when undertaking asynchronous programming.

Code to be Tested

The following methods in based on the Northwind database and it computes the running totals for each customer of the store including the number of orders and how much they have spent historically.  The method is an operation of a service called CustomerOrderAggregation and it takes a search criteria containing CustomerID.  The idea is if the search criteria CustomerId value is set then the computation is executed for that customer and if not set then the computation is done for all customers.

  public async Task<IQueryable<CustomerOrderStatistic>> CustomerOrderSummaryAsync(  
       CustomerOrderSearch criteria)  
       var result = await customerRepository  
           r => r.CustomerID.Equals(criteria.CustomerId))  
           c => c.CustomerID,  
           o => o.CustomerId,  
           (c, o) => new { c, o })  
           x => x.o.DefaultIfEmpty(),  
           (x, l) => new CustomerOrderStatistic  
             CustomerId = x.c.CustomerID,  
             ContactName = x.c.ContactName,  
             TotalPayments = l != null ? l.TotalPayments : 0,  
             TotalOrders = l != null ? l.TotalOrders : 0,  
       return result.AsQueryable();  

OrderOrderDetailsStatistics(criteria) executes a join between Order and Order_Details on OrderId and groups by Order.CustomerId and this is how we learn the running totals:

 private IQueryable<CustomerOrderGrouped> OrderOrderDetailsStatistics(  
       CustomerOrderSearch criteria)  
       return orderRepository.GetAll()  
           o => o.OrderID,  
           od => od.OrderID,  
           (o, od) => new { o, od })  
         .GroupBy(g => new { g.o.CustomerID })  
         .Select(grp => new CustomerOrderGrouped  
           CustomerId = grp.Key.CustomerID,  
           TotalPayments = grp.Sum(row => (row.o.Freight.HasValue ? row.o.Freight.Value : 0) +  
                          (row.od.UnitPrice * row.od.Quantity)),  
           TotalOrders = grp.Select(row => row.o.OrderID)  
           r => r.CustomerId.Equals(criteria.CustomerId));  

Unit Testing with Moq

The service construction is as follows:

 public CustomerOrderAggregation(  
       ICustomerRepository customerRepository,  
       IOrderDetailsRepository orderDetailsRepository,  
       IOrderRepository orderRepository)  
       this.customerRepository = customerRepository;  
       this.orderDetailsRepository = orderDetailsRepository;  
       this.orderRepository = orderRepository;  

hinting that for the unit tests using Moq three repositories need to be mocked.  Repositories GetAll() is a generic which returns an IQueryable therefore to be able to execute the queries against the mocked IQueryable GetAll() IQueryable needs to be implemented.  This is explained in the reference provided in this post:

 var data = new List<Customer>  
        new Customer  
             CustomerID = "LAUGB",  
             CompanyName = "Laughing Bacchus Wine Cellars",  
             ContactName = "Yoshi Tannamuri",  
             ContactTitle = "Marketing Assistant"  
 var mockSet = new Mock<DbSet<Customer>>();   
 mockSet.As<IQueryable<Customer>>().Setup(m => m.Provider).Returns(data.Provider);   
 mockSet.As<IQueryable<Customer>>().Setup(m => m.Expression).Returns(data.Expression);   
 mockSet.As<IQueryable<Customer>>().Setup(m => m.ElementType).Returns(data.ElementType);   
 mockSet.As<IQueryable<Customer>>().Setup(m => m.GetEnumerator()).Returns(() => data.GetEnumerator());
 customerRepositoryMock.Setup(c => c.GetAll()).Returns(mockSet.Object);

OrderRepository and OrderDetailsRepository GetAll() would need to me mocked using the same procedure for Order and Order_Details respectively.  However, trying to use the above mocked repositories will fail for two reasons.

First AsNoTracking() needs to be mocked as well:

mockSet.As<IQueryable<Customer>>()Setup(c => c.AsNoTracking()).Returns(dbSet.Object);

However, the test for the async method would fail with the following exception:

"System.InvalidOperationException: The source IQueryable doesn't implement IDbAsyncEnumerable. Only sources that implement IDbAsyncEnumerable can be used for Entity Framework asynchronous operations. For more details see"

The solution to the error is in the link provided in the exception message!!!  The reference is telling us that to be able to process the async method a DbAsyncQueryProvider needs to be created.  I selected to follow the same solution discussed in the msdn post because it is reusable.  The only difference is that the mocked DbSet was encapsulated in a static class with a static generic method to facilitate reusability.

 public static class MockDbSet  
     public static DbSet<T> GetQueryableMockDbSet<T>(params T[] sourceList) where T : class  
       var queryable = sourceList.AsQueryable();  
       var dbSet = new Mock<DbSet<T>>();  
         .Setup(m => m.GetAsyncEnumerator())  
         .Returns(new TestDbAsyncEnumerator<T>(queryable.GetEnumerator()));  
         .Setup(m => m.Provider)  
         .Returns(new TestDbAsyncQueryProvider<T>(queryable.Provider));  
       dbSet.As<IQueryable<T>>().Setup(m => m.Expression).Returns(queryable.Expression);  
       dbSet.As<IQueryable<T>>().Setup(m => m.ElementType).Returns(queryable.ElementType);  
       dbSet.As<IQueryable<T>>().Setup(m => m.GetEnumerator()).Returns(() => queryable.GetEnumerator());  
       dbSet.Setup(c => c.AsNoTracking()).Returns(dbSet.Object);  
       return dbSet.Object;  

Now repositories are mocked this way in the test setup method:

     public void Setup()  
       // Arrange - Mock Repositories  
       var customerRepositoryMock = new Mock<ICustomerRepository>();  
       var orderDetailsRepositoryMock = new Mock<IOrderDetailsRepository>();  
       var orderRepositoryMock = new Mock<IOrderRepository>();  
       // Arrange - Setup return values   
       customerRepositoryMock.Setup(c => c.GetAll()).Returns(MockDbSet.GetQueryableMockDbSet<Customer>(  
           new Customer  
             CustomerID = "LAUGB",  
             CompanyName = "Laughing Bacchus Wine Cellars",  
             ContactName = "Yoshi Tannamuri",  
             ContactTitle = "Marketing Assistant"  
          new Customer
          CustomerID = "JMARINO",  
             CompanyName = "Marino's",  
             ContactName = "Jose Marino",  
             ContactTitle = "Principal"  

       // Arrange - setup order details  
       orderDetailsRepositoryMock.Setup(o => o.GetAll()).Returns(MockDbSet.GetQueryableMockDbSet<Order_Detail>(  
           new Order_Detail { OrderID = 1, ProductID = 23, UnitPrice = 7.20m, Quantity = 10 },  
           new Order_Detail { OrderID = 1, ProductID = 41, UnitPrice = 7.70m, Quantity = 20 },  
           new Order_Detail { OrderID = 1, ProductID = 77, UnitPrice = 10.40m, Quantity = 5 },  
           new Order_Detail { OrderID = 2, ProductID = 24, UnitPrice = 4.50m, Quantity = 5 },  
           new Order_Detail { OrderID = 2, ProductID = 52, UnitPrice = 7.00m, Quantity = 5 },  
           new Order_Detail { OrderID = 3, ProductID = 13, UnitPrice = 6.00m, Quantity = 7 },  
           new Order_Detail { OrderID = 3, ProductID = 25, UnitPrice = 14.00m, Quantity = 5 },  
           new Order_Detail { OrderID = 3, ProductID = 70, UnitPrice = 15.00m, Quantity = 5 }));  
       // Arrange - setup orders  
         o => o.GetAll())  
               new Order { OrderID = 1, CustomerID = "LAUGB", Freight = 4.65m },  
               new Order { OrderID = 2, CustomerID = "LAUGB", Freight = 0.94m },  
               new Order { OrderID = 3, CustomerID = "LAUGB", Freight = 4.33m }));  
       // Arrange - create instance of service and inject mocked repositories  
       _customerOrderAggregationService = new CustomerOrderAggregation(  
         orderDetailsRepositoryMock.Object, orderRepositoryMock.Object);  

and the service is tested like this:

     public async Task Test_CustomerOrderSummaryAsync_ForExcistingUser_Returns_Summary_With_One_Group()  
       // Arrange - Create search criteria  
       var criteria = new CustomerOrderSearch  
         CustomerId = "LAUGB"  
       // Act - Call Service async method  
       var result = await _customerOrderAggregationService  
       // Assert - validate only one group is present  
       var resultList = result.ToList();  
       Assert.IsTrue(resultList.Count == 1);  


  1. Mocking IQueryable using Moq for a repository of T the mocked DbSet IQueriable needs to setup: query Provider, query Expression, query ElementType, GetEnumarator()
  2. When testing async queries the mocked DbSet needs to set up e GetEnumerator() for an IDbAsyncEnumerator and setup and AsyncQueryProvider


  1. Async Programming: Unit Testing of Asynchronous Code: 
  2. Explanation to InvalidOperationException when testing EF 6.x async queries:
  3.  Detailed explanation and reference code to be able to use moq mock objects in blocking and non blocking scenarios: