IExtendable while (this.IsAlive) self => self.UpdateAll()

13Sep/141

Seattle Code Camp 2014

I gave 2 presentations at Seattle Code Camp today.

The first was a talk about our internship program. I'm still trying to start the conversation on this one. So far it appears no one is talking about this topic. My powerpoint is here: Scaling Craftsmanship Through Apprenticeship. It's not much more than just a memory-jog for me, but they were asked for so I'm posting them.

The second talk was about Unit Testing Your Javascript. This one sort of went sideways when Chrome refused to load my demo site. That was a challenge! Still, I think it went off okay. The unfortunate reality is that unit testing in Javascript is still pretty hard.  It still feels like a lot of duct tape and baling work to make it work. That said, I've put together a demo application that shows how we do it at work.

Thanks to everyone who attended my presentations. I hope you enjoyed them!

Filed under: Uncategorized 1 Comment
17Jan/140

Running a Software Development College Internship

Introducing an college internship program into a development organization can be a difficult challenge. There are precious little resources available on the topic. Here are some thoughts I’ve put together after working with interns over the last year and a half.

What Does Your Department Want?

Deciding what value you hope to gain will go a long way toward helping you decide what the features of a good internship program should be. From the intern’s perspective, they want an opportunity to learn, to network, and to gain experience. If you don’t have anything that you want out of offering an internship, it will be hard for you to run it effectively.

For our part, we want to expand our existing “learning organization” culture. We regard our interns as potential sources of hiring. We want to improve the overall quality of software in general by teaching new programmers some of our hard-won knowledge of principles, patterns, and practices. We want to aid our business by making interns available to work on small-scale projects that almost never get prioritized.

Establish a Primary and Secondary Mentor

Each intern should have a primary mentor who is responsible for directing their day-to-day activities. In addition, each intern should have at least one adjunct mentor who checks in with them each week to see how they are doing. Often a different ear will hear things that the primary mentor will not, such as if the primary mentor is moving too fast or too slow, or if a different teaching technique would be helpful. This feedback is important to gain early so that the learning process can be tailored to the individual intern.

Patience

As a mentor and trainer to interns you will be confronted with the sheer number of concepts, processes, tools, techniques that you simply take for granted. In our shop interns have routinely never seen source control, build servers, unit testing, code bases with more than a few hundred lines, third party tools such as ReSharper, third party libraries such as jQuery, and project management tools. We have to teach them all of those things before they can be productive in our business.

In its current incarnation, our interns spend 20+ hours per week in the office. Below are the materials that I really want them to learn over the course of their internship. Time is short and there is a lot to learn, but the mentor should resist the desire to go too fast. I’m covering concepts with my interns that it took me 10 years to learn. I’m trying to introduce them to these concepts so that they understand them well enough to begin using them in just over a month. This is an enormous challenge for both the intern and the mentor. The mentor needs to remain patient and allow the intern time to digest and practice what has been covered so far before diving into the next subject.

Most importantly, do not push the interns to learn topics that build on other topics they do not yet understand. For example, don’t teach mocking tools before they’ve learned the basics of Test Driven Development.

Practice

Interns need time to practice the material you are teaching them. Remember, you have been doing this for years. They’ve been doing this for days. The difference is important. Given them breakable toys to work on. Teach them the concept. Pair with them to practice the technique the first time. Follow up with a different practice exercise for them to do on their own to be sure they have it. If you can’t find a good practice exercise, create one. If the intern does not seem to be “getting it” from you, consider having the intern work with someone else for the material in question. Sometimes an alternate perspective is all it takes to make the material sink in. If that still doesn’t work, move on to something else and come back to the material later.

Pairing

It can often be hard for interns to “get started” with whatever task they’re supposed to be practicing. For example, after reading about Test Driven Development, they may feel confident that they understand the concepts. In practice however, they are often unable to write their first tests. As the primary mentor, you will need to work directly with them to help them “get over the hump.” By pairing with them, you will see concretely what they do and do not understand. You should give broader context for what they do understand, and direct their learning and practice toward what they do not understand.

Training

Learning is what the intern is here for, but where do you start? How do you work with someone with no prior work experience? How do you teach them all those things you take for granted? We want to welcome new people into the software development industry, but we don’t want to sacrifice code quality.

I accomplish this in a couple of ways.

The first thing I do with a new intern is setup an online Kanban board with them. I’m using Trello right now. This is important to keep track of each intern’s progress. Further, the intern’s learning is a project in it’s own right, so it’s natural to treat it the way we treat other projects.

During the first month they are given the time and space they need to read, watch training videos, and practice what they’ve learned on breakable toys. I spend 1 to 3 hours per day working side-by-side with the intern during this period to guide their learning. The order of the learning is not terribly important, though there are logical dependencies between some concepts that need to be observed.

I require that all of their work is placed into source control. I want the intern to get comfortable with github right away as all work should be done using source control. Many interns have never worked with source control at all, so learning git right away can be challenging. A good exercise for learning github is to have them import their school projects into github. If the intern likes the command-line that’s fine, but I usually tell them about great GUI tools such as SourceTree. I find that the GUI really helps people new to Git grok the concepts. (I still use the GUI myself Winking smile .)

The other thing I think it’s important to discuss early is the value of clean code. Our interns are given copies of Clean Code and Clean Coder on their first day. Of all the books listed, this is the one it’s most important to me that they read. A recent idea I had about how to practice cleaning code is have the intern use their own school projects (now conveniently located in github) as refactoring exercises.

An intern is not going to master any of the content (that takes continued practice over years), but they will be much further ahead starting their career armed with a basic grasp of the principles, patterns, and practices that it took the rest of us years to learn. The learning should be aggressive and focused on making them productive in your environment as quickly as possible.

Real Code

It’s natural that interns would want to work on something useful for the business. The biggest bottlenecks to making that happen for us are process compliance, automated testing, their ability to navigate large projects, and knowledge of software architectural patterns. Our shop places a high value on automated testing for production code. TDD is difficult for experienced developers to learn, so asking an intern to do it on the first day might be a bit much. This is why we don’t expect useful code out of our interns in the first month. That time is to be spent learning.

After the first month we begin introducing them to code bases we intend to use. These code bases are typically larger than the code that they have been working with in school, so it’s important to spend some time teaching them how to navigate the projects. This time should include a discussion of the logical division of responsibilities inside the project as well as mundane items such as useful keyboard shortcuts in whatever developer tools you are using.

Internship Curriculum

Below is the basic curriculum I put interns through in their time with us. I encourage them to get through as much of the reading and training materials as possible. I start putting them on real code after the first month. I pair with them to find out what they do and do not understand. I do not push them to study topics that build on concepts they do not already grasp. This curriculum is tailored for our environment. We are a Kanban, C#, Continuous Integration shop that highly values clean code. Your curriculum should be tailored to the tools that you use every day in your work.

28Sep/130

Onion Architecture Presentation Resources

Thanks to everyone who attended my presentation at #SeattleCodeCamp this morning!

The code I demoed this morning is currently on the “develop” branch on github.

Here are some of the resources for further reading I alluded to.

I had some additional thoughts for future revisions of the presentation.

  1. OA is not just about coding to interfaces. It’s also about coding to the right category of interfaces.
  2. My presentation is in C#, but the same principles apply in any programming language. The implementation details in other languages may differ.
  3. Every recommended approach to Onion has a “fat” layer where the important code is. Other layers are basically façades and coordinators.
  4. In the future, I’d like to show my code diagram first, then show the code, then show the other Onion diagrams.
  5. I need to update my image for my code diagram as the font doesn’t show up well on washed out projectors.

I’d also like to find a DDD implementation of OA and at least one written in another language (not Java).

22Aug/130

Isg.EntityFramework 0.9.0 Released (Bug Fix)

Release Notes

  • Fixed a bug in TypeInterceptor in which IsTargetEntity() was not being called before passing the handling down the inheritance chain.
19Aug/130

Don’t Unit Test NHibernate: Use Generic Repository

I was reading this stack overflow question: How can I solve this: Nhibernate Querying in an n-tier architecture?

The author is trying to abstract away NHibernate and is being counseled rather heavily not to do so. In the comments there are a couple of blog entries by Ayende on this topic:

The false myth of encapsulating data access in the DAL

Architecting in the pit of doom the evils of the repository abstraction layer

Ayende is pretty down on abstracting away NHIbernate. The answers on StackOverflow push the questioner toward just standing up an in-memory Sqlite instance and executing the tests against that.

The Sqlite solution is pretty painful with complex databases. It requires that you set up an enormous amount of data that isn’t really germane to your test in order to satisfy FK and other constraints. The ceremony of creating this extra data clutters the test and obscures the intent. To test a query for employees who are managers, I’d have to create Departments and Job Titles and Salary Types etc., etc., etc.. Dis-like.

What problem am I trying to solve?

In the .NET space developers tend to want to use LINQ to access, filter, and project data. NHibernate (partially) supports LINQ via an extension method off of ISession. Because ISession.Query<T> is an extension method, it is not stubbable with free mocking tools such as RhinoMocks, Moq, or my favorite: NSubstitute. This is why people push you to use the Sqlite solution—because the piece of the underlying interface that you want to use most of the time is not built for stubbing.

I think that a fundamental problem with NHibernate is that it is trying to serve 2 masters. On the one hand it wants to be a faithful port of Hibernate. On the other, it wants to be a good citizen for .NET. Since .NET has LINQ and Java doesn’t, the support for LINQ is shoddy and doesn’t really fit in well the rest of the API design. LINQ support is an “add-on” to the Java api, and not a first-class citizen. I think this is why it was implemented as an extension method instead of as part of the ISession interface.

I firmly disagree with Ayende on Generic Repository. However, I do agree with some of the criticisms he offers against specific implementations. I think his arguments are a little bit of straw man, however. It is possible to do Generic Repository well.

I prefer to keep my IRepository interface simple:

    public interface IRepository : IDisposable
    {
        IQueryable<T> Find<T>() where T: class;

        T Get<T>(object key) where T : class;

        void Save<T>(T value) where T: class;

        void Delete<T>(T value) where T: class;

        ITransaction BeginTransaction();

        IDbConnection GetUnderlyingConnection();
    }

 

Here are some of my guidelines when using a Generic Repository abstraction:

  • My purpose in using Generic Repository is not to “hide” the ORM, but
    • to ease testability.
    • to provide a common interface for accessing multiple types of databases (e.g., I have implemented IRepository against relational and non-relational databases) Most of my storage operations follow the Retrieve-Modify-Persist pattern, so Find<T>, Get<T>, and Save<T> support almost everything I need.
  • I don’t expose my data models outside of self-contained operations, so Attach/Detach are not useful to me.
  • If I need any of the other advanced ORM features, I’ll use the ORM directly and write an appropriate integration test for that functionality.
    • I don’t use Attach/Detach, bulk operations, Flush, Futures, or any other advanced features of the ORM in my IRepository interface. I prefer an interface that is clean, simple, and useful in 95% of my scenarios.
  • I implemented Find<T> as an IQueryable<T>. This makes it easy to use the Specification pattern to perform arbitrary queries. I wrote a specification package that targets LINQ for this purpose.
    • In production code it is usually easy enough to append where-clauses to the exposed IQueryable<T>
    • For dynamic user-driven queries I will write a class that will convert a flat request contract into the where-clause needed by the operation.
  • I expose the underlying connection so that if someone needs to execute a sproc or raw sql there is a convenient way of doing that.
6Aug/137

Isg.EntityFramework 0.8.0 Released

InterceptionContext is now passed to TypeInterceptor methods and ChangeInterceptor methods. This may result in breaking changes depending on if and how you have inherited those classes, but I’ve done my best to preserve existing behavior. I marked the obsolete methods as such.

The purpose of this change is enable the scenario where you want to write a log-record back to the database when a record is saved or deleted.

Update:

0.8.0 did not contain the updated assemblies.

0.8.1 does.

What happened?

My build server is configured so that it only creates and publishes packages from the last pinned build. I forgot to pin the build that has the changes. I've pinned the build and republished 0.8.1. I've created a workitem for myself to separate package creation from package publication so that I can inspect the package before it's sent to Nuget.

30Jun/135

Review of “Guitar Practiced Perfectly” Software

Overall

Guitar Practiced Perfectly is a piece of software that helps a guitarist manage and plan practice routines. It includes 300 or so practice routines out of the box. Routines can be organized into sessions. Sessions can be organized arbitrarily, but the software supports daily sessions. It’s written in Adobe Air so it will run on Mac and PC. I’m running on Windows 8 64-bit.

I’ve only used the software for one practice session so far. The overall effort is very good. As far as I know, it’s the only software of its kind. At $50 US, it’s a little pricey to buy without a trial.

image

 

Missing Features

  • I should be able to create my own routines. This is a huge gap in the software. For example, I'd like a version of the C major pentatonic that includes the minor 3rd and the diminished 7th. Or I’d like a routine in which I play a scale through ascending keys.
  • When I drag/drop an element between tree elements, I should be able to choose "Copy" or "Move."
  • In addition to being able to create a new routine, I’d like to be able to clone an existing routine and modify it.

Bugs

  • I've noticed that if I'm playing an exercise and change the tempo then it stops playing sound. I have to close/reopen the software to get it to play sound again.
  • Drag/Drop a routine within a session doesn’t work. This makes changing the order of the routines hard.

Usability Problems

  • The use of accordion style controls for the session menus makes it hard to understand that you can drag/drop exercises between accordion tabs. In general, accordions should not be used when data is shared across panels.
  • The fact that the screen elements are static is irritating. It would be nicer if I could move things around. The best UI I've seen for this sort of thing is in Microsoft Visual Studio. Each panel is draggable and dockable on its own. I don't know if Adobe Air gives you this kind of flexibility, but it would be nice, and it would make the drag/drop operations easier to manage as "Session by Weekday" could be docked to a different screen area than "Session by Skill Level."
  • The user should be able to drag/drop more than one exercise at a time. I found this annoying when I was trying to drag all of a certain category of exercise to my Sunday routine. I had to do them one at a time.
  • The labels that control Tempo, Lead In, Repeat, etc react to the mouse as if they were buttons. Clicking them doesn't do anything. This is confusing. They should either just be labels, or open some kind of advanced editing screen.
  • Having to choose between Music and Metronome is painful. They should have independent volume controls.The existing either-or functionality forces me to into a tricky volume balancing act with my amp.
  • Help->About menu should include the software version. The fact that the software version is missing from the UI makes it hard to tell if you are running the latest.
  • The main window should include a standard control box for changing screen size, minimize, and maximize functionality.
  • I think it should be impossible to delete system-defined routines and sessions. This is scary functionality as I could get rid of something very useful.

Overall

I like Guitar Practiced Perfectly very much and I’ll get a lot of use out of it. However, it’s not the software I was hoping it was. The lack of routine-creation and editing functionality means it misses the mark by quite a large margin. Some of the UI constraints make working with sessions very hard. For an intermediate player such as myself, it will definitely help me take my playing to the next level. However, I’ll not be able to use it to integrate my teacher’s lessons into my daily practice.

Final Score

70%

21Apr/136

Isg.EntityFramework 0.7.0 Released–Bug Fix

Issues Fixed

  1. ChangeInterceptor.OnAfter not working correctly.

The cause of the bug is that EntityFramework resets the EntityState to UnChanged after writing the object to the database. This means that I cannot tell which operation was performed on the entity unless I memoize the state before the operation. The effect of this change is that I can no longer get the EntityState of the item before the operation from the DbEntityEntry.

Breaking Changes

If you are inheriting from TypeInterceptor or ChangeInterceptor the signature of OnBefore and OnAfter has changed.

The new signatures are

 protected override void OnBefore(DbEntityEntry item, EntityState state)
 protected override void OnAfter(DbEntityEntry item, EntityState state)

16Apr/130

Testing Ninject Bindings

I recently had a subtle production bug introduced by creating more than one Ninject binding for a given interface to the same instance.

I wanted to be able to see what bindings existed for a given interface, but Ninject does not provide an easy way to do that.

This gist contains an extension method I wrote (with the help of a StackOverflow article) to acquire this information.

As this code relies on using reflection to get a private member variable, this code is brittle in the face of a change in the implementation of KernelBase. In the meantime, it works on my machine.

16Apr/130

Onion Architecture: An Opinionated Approach Part 2, Anemic Data Models

Anemic Data Model is my term for a domain model indicating entities and their relationships to other entities, but having little or no business behavior. It basically serves as a contract for a data store. It’s purpose is structural, and often to provide ease of queryability.

In ShowPlanner, the domain is about planning and selling tickets to musical events called “shows.” Venues contain one or more Stages, and a Show can consist of one or more Performances on one or more Stages at a Venue. Tickets are sold to a Show.

DataModel

This data model represents the universe of entities, attributes, and relationships that the ShowPlanner application will interact with at this time. These models have no methods or functions, no behavior of any kind.

The Problem of Behavior

Why no behavior? Putting behavior in domain models raises some difficult design questions. How do the domain objects get their dependencies? Which domain object should the method or methods that control behavior go in?

Let’s take a simple case. Suppose you want to model what happens when a Ticket is purchased by a Customer. When a show is created, a number of tickets are created as well. When a Customer buys a Ticket, the ticket will be marked as sold.

Ownership

Generally speaking it’s very seldom that we write basic CRUD applications in an enterprise environment. Application behavior tends to live in the relationships and what happens when certain kinds of relationships are created and destroyed. This means that application operations often involve the state of multiple domain objects directly and indirectly involved in the relationship that is changing.

There are several possible ways to model this operation.

    public class Customer
    {
        public int? CustomerId { get; set; }

        public IList<Ticket> Tickets { get; set; }

        [Required]
        public string Name { get; set; }

        public void Purchase(Ticket ticket)
        {
            ticket.SoldTo = this;
            ticket.Sold = true; 
        }
    }

 

Or

    public class Ticket
    {
        public int? TicketId { get; set; }

        public int? ShowId { get; set; }
        [Required]
        public Show Show { get; set; }

        public int? CustomerId { get; set; }
        public Customer SoldTo { get; set; }

        public bool? Sold { get; set; }

        [Required]
        public decimal Price { get; set; }

        public void SellTo(Customer customer)
        {
            this.Sold = true;
            this.SoldTo = customer;
        }
    }

Or

    public class Show
    {
        public int? ShowId { get; set; }

        public IList<Ticket> Tickets { get; set; }

        [Required]
        public string Title { get; set; }

        public void SellTicket(Customer customer, Ticket ticket)
        {
            ticket.Sold = true;
            ticket.SoldTo = customer;
        }
    }

 

Which domain object should own the method for selling the ticket? It will depend on who you ask. When a given operation affects multiple entities in the Domain, there is no objective way to decide which entity gets the behavior. The method performing the operation has no natural home.

Dependencies

Let’s assume you secure agreement that Customer should own this operation. You’re happily coding along on something else when a few weeks later your customer tells you that when the ticket is sold a message needs to be sent to a billing system. The messaging system is represented by an interface called IMessageSender. What happens in the domain model now? How does the Customer class get a reference to the MessageSender implementation?

You could do this I guess:

        public void Purchase(Ticket ticket, IMessageSender messageSender)
        {
            ticket.SoldTo = this;
            ticket.Sold = true;

            messageSender.Enqueue(new BillForTicketMessage(this, ticket));
        }

But that’s an ugly road to walk down. You’ll start expanding dependencies when you need to add logging, authorization, validation, and a host of other concerns. Suddenly what started out as a very simple method on domain model full of complexity.

Constructor injection is not viable if I’m expecting to use an ORM to retrieve my Customer instance. Assuming you could make that work, you have to consider that with the addition of each new operation involving Customer, you’ll be adding still more dependencies which will turn Customer into more of a GOD class than will be supportable.

Wouldn’t’ design-by-composition work better?

Designing the Domain Models

I said earlier that “domain models as merely a means of persisting the state of the application.” To my way of thinking, this is their core purpose. To that end, they should effectively act as a contract to the underlying data store used by your application. They should support both queryability and data modification and be well-organized.

Queryability

To support queryability, data models should be fully connected. This just means that any relationships between entities should be referentially  expressed. Prefer Performance.Show over Performance.ShowId. Some ORM’s such as Entity Framework support using both the Id and the reference. For others, such as NHibernate, having both properties is an issue. When faced with a choice, prefer a reference over an Id.

Data Modification

To support data modification, your data models should contain all the fields used in the database. I was writing an integration test recently and I needed to create some test data in Sql Server. As I tried to insert one of my entities, I discovered that field required by the database was not actually on the model. The original developer had only populated the fields he needed for the specific operation he was writing which resulted in additional work and testing for me. It also exposed a lack of integration test coverage for any operation involving this entity as it was impossible to create new records using existing code.

Organization

Data models are the center of the onion. They should be in their own assembly or package both to make them easier to find and modify, and to prevent other developers from violating the Dependency Depth principle by referencing higher layers.

Do’s
  • Put your data models in their own project or assembly. This makes them easy to find. They are the innermost circle in your application, so this project should have next to no dependencies on anything else.
  • If you’re tools set supports it, maintain a class diagram of the models and their relationships. The diagram above was generated by Visual Studio.
  • Prefer referential relationships over using Id’s to identify related data.  Use both if your ORM supports it.
  • This should go without saying, but use an ORM.
  • In the anal-retentive list of things to consider
    • List the primary key first.
    • List single-entity references second.
    • List collection references third.
    • List the entity’s fields last.
    • List audit data (create date, create user, etc) dead last.
    • Alphabetize fields. Why? Because with larger data models it gets really hard to find the field you’re looking for in an unsorted list. This is an easy thing to habitualize and saves a good bit of headache down the road.
  • In .NET, use System.ComponentModel.DataAnnotations to attribute your models metadata when it is known.
    • Especially use StringLength because it produces a nicer error message than “String or binary data would be truncated” when using SQL Server as the database.
Don’ts
  • Don’t put behavior on the models.
  • Don’t accept dependencies in the models.
  • Don’t put ORM-specific attributes on the models unless you have no other choice.
  • Don’t put anything on the models that isn’t actually in your data store.
    • This is another way of saying “don’t put behavior on the models.” But I’ve seen developers put properties on models that they calculate and set in the course of one operation and that isn’t used in other operations. This breaks down when another operation wants to use the calculated value.
  • Don’t use data models in your UI. In web applications, this means don’t use data models in your pages and controllers. Use View Models and some sort of Request-Response api instead.

This is Part 2 of a series

Disclaimer: This series of articles is intentionally opinionated. From an architectural perspective I am much more interested in clearly defining each layer than I am in the choice of specific implementation pattern. However, an architecture doesn’t exist without the details that make it up, so I must choose some implementation pattern so that the architecture can be revealed. Since I’m the one writing the series, I’ll choose implementation patterns I like. Smile If you have a better idea, take a fork of ShowPlanner and share it!