Tag: entity framework
Demo Code for EF4Ent Sessions
Posted by bsstahl on 2011-06-26 and Filed Under: development
I previously posted the slides for my Building Enterprise Apps using Entity Framework 4 talk here. I can now post the source code for the completed demo application. That code, created for use in Visual Studio 2010 Ultimate, is available in zip format below. This is the same code that was demonstrated at Desert Code Camp 2011.1 and SoCalCodeCamp 2011 as well as the New Mexico .NET User’s Group (NMUG).
Code Analysis Rules
Posted by bsstahl on 2011-06-07 and Filed Under: development
FxCop, the built-in code-analysis tool in Visual Studio, is the first thing I check when doing a code review. If Code Analysis is enabled for a project, setup properly, and its rules have not been overridden, this tool will help maintain consistency in the code, even if that code is worked on by multiple developers. FxCop also does a good job of identifying if some common mistakes have been made, such as not disposing of an IDisposable object, and can identify things that will help the compiler do its job better, such as ensuring that assemblies which expose public objects identify whether or not they are intended to be CLS compliant.
In order to get these benefits, code analysis must be enabled for each project and a rule set must be selected. Because adding code-analysis to existing assemblies can be a bit painful, it is recommended that you enable this analysis as soon as a project is created in Visual Studio. To enable code analysis for an assembly, select the project properties, go to the Code Analysis tab, and check the “Enable Code Analysis on Build (defines CODE_ANALYSIS constant)” box.
The default rule set that will be run during code analysis is called “Microsoft Minimum Recommended Rules”. This is a very small set of rules that is a good one to enable if you are starting to do code analysis on a previously coded assembly. If however, you are starting clean, I highly recommend starting with either the “Microsoft All Rules” rule set, or your own version of that set, since this rule set will provide the most benefit in all areas of analysis. To create your own rule sets, select the set you wish to modify and press the “Open” button next to the rule set drop-down. Once opened, you can make any changes you wish, and use the File –> Save-as menu item to save the rule set with a different file name. New rule sets will automatically appear in the drop-down menu. You can use the properties tab to update the Name and Description of the set, and the rules editor to enable or disable individual rules. You can also define, for each rule, whether failures are ignored, result in a warning, or generate a compilation error. I highly recommend setting all rules that you want to enforce to cause errors since they can always be overridden if necessary but will likely be missed if they only result in warnings.
For my projects, I use one of several rule sets that I have set up, all of which are slight modifications to the “Microsoft All Rules” rule set. I will detail the rule set changes I make and overrides that I allow in each set of circumstances below. I encourage you to experiment with these rule sets to determine the optimum configuration for your projects.
- Modify the “Microsoft All Rules” rule set so that all rules result in an error. The easiest way to do this is to use the “group by” drop-down to order all rules by “Target Type”. The only type found here should be “Managed Code”. With this single group collapsed, use the Action drop-down to select “Error” for all rules.
Entity Framework Projects
- The Entity Framework requires navigation properties of entities to be read-write, a violation of rule CA2227, “Collection properties should be read only”. For projects utilizing the Entity Framework, as well as those designed for use within the entity framework (such as entity POCO libraries), the action of this rule may be set to “Warning” to prevent compilation errors whenever entities with navigation properties are built.
Projects Deployed to Internal Company Servers (and not GAC’ed)
- Assemblies that will not be deployed to the GAC and will remain on secure, internal servers do not need to have a strong name. Thus, rule CA2210, “Assemblies should have valid strong names”, can be permanently over-ridden or have its action set to “None”.
- For projects that are never to be localized to a foreign culture, you can set the action for rule CA1303, “Do not pass literals as localized parameters”, back to “Warning”. I find this rule to be especially incorrect when I am writing logging code within my methods (unless using aspect-orientation) because the logging code also serves as functional code-comments if the literals are included in the method calls.
- Many console apps ignore the command-line parameters passed-in to the main method, a violation of rule CA1801, “Review Unused Parameters”. Most of the time, this rule is valuable since you don’t want to have parameters to methods that are never used, however, since we cannot change the parameters to the main method of a console app, but may not wish to use them, this rule can be set to generate a warning in console applications, or can be simply overridden for the parameters to the main method of each console app. This rule may also be violated temporarily when a method has been stubbed but not yet implemented. In that case, the rule should be overridden in code similar to rule CA1822 below.
Other (More Temporary) Modifications
- Rule CA1822, “Mark members as static”, is violated when a method in a class does not use any of the other non-static members of the class. This is always true when the method has not yet been implemented (is only a stub). Prior to the method being implemented, this rule should be overridden in code. The override should be removed from the code once the method has been implemented.
- Rule CA1040, “Avoid empty interfaces” is often violated temporarily in TDD/BDD because interfaces may be created without methods and then be built-up as needed by the use-case. Prior to the interface being defined, this rule should be overridden in code. The override should be removed from the code once the interface has been defined.
I have found using Code Analysis to be a good way to improve the maintainability of my applications, especially when the app is being worked on by multiple members of a project team. The FxCop tool, built into Visual Studio’s Ultimate and Premium editions, is one of a number of tools and techniques I use to keep my code as maintainable and extensible as possible, resulting in the lowest possible total cost of ownership (TCO). In future articles, I will explore additional tools and techniques I use for this purpose.
Desert Code Camp Presentation
Posted by bsstahl on 2011-04-02 and Filed Under: event development
Thanks to all of the organizers, speakers, sponsors and attendees of Desert Code Camp 2011.1. This is the first time that I’ve presented at a Code Camp and it was a fantastic experience for me. My session, Building Enterprise Apps using Entity Framework 4, was very well attended with 35 people cramming, standing-room-only, into a room with a capacity of 28 (please don’t tell the Fire Marshall). The demos went very well (everything worked as it was supposed to) and the feedback I’ve gotten so far was entirely positive.
I will be posting some additional information from the session shortly, including the sample code and the changes I make to the Microsoft All Rules code analysis ruleset, but I wanted to get the session slides up as quickly as possible.
If you have any additional feedback on the session, please feel free to contact me here, by Twitter @bsstahl or by email as shown in the slide deck.
DCC 2011.1 -- Building Enterprise Apps using Entity Framework 4
Decorating Partial Class Members in C#
Posted by bsstahl on 2011-03-08 and Filed Under: development
Anyone who uses code generation more than trivially in their .NET solutions knows how difficult it is to add metadata to a member of a generated class, even if that class is marked as partial. Partial classes are terrific for adding members to generated classes, and even allow you to change metadata and other information about the class itself, such as by adding an interface that it implements. You cannot however, modify an existing member of the class by marking it to not be serialized, or to make it a part of a WCF data contract. I believe, as more and more code is generated by .NET developers using Entity Framework, wsdl.exe and other proxy generation tools, or even T4 directly; we will see a greatly increased need for a workable solution to this problem.
The most common work-around for this problem today is the use of “buddy classes” where a separate class is created to hold the metadata. A good example of this type of solution can be found in ASP.NET Dynamic Data. However, as you might imagine, this type of implementation has some fairly severe drawbacks. For one, it requires some sort of mechanism for unifying the functionality of the two classes. An example of this is the case where we have a property on an Entity Framework POCO that should not be serialized when we serialize the rest of the class. We cannot serialize the POCO correctly unless we use a custom serializer that is aware of the metadata in the buddy class. We have similar problems if we are trying to use a generated base class as the output of a WCF service. If the [DataContract] attribute is not already on the generated code (which requires a reference to the System.Runtime.Serialization library) we will have to create a separate object that implements the DataContract to be exposed by the service. In most cases, this object will be an almost exact duplicate of the state features of the original object, forcing the replication of some code, even if that code is just the properties of the object.
There is a feature that has been proposed in the C# language for some time now that would allow this type of behavior within a single class. This feature would use the keyword existing to allow the duplication of the definition of partial class members into non-code-generated files so that those members can be decorated with additional metadata without risk of being overwritten when the automatic code is regenerated, and without duplicating the functionality in the member. Unfortunately, it appears that this feature is not going to make it into the next version of C# and is at risk of not being in the following version as well. In an email exchange, Mads Torgersen, C# Program Manager at Microsoft, stated that
…maybe we’re looking at C# next-next-next before the next big set of new feature ads makes it in [to the language].
One of the reasons (although certainly not the only reason) for this delay, as explained by Mads, is what really struck me:
To be honest the clamoring for the “existing” feature has died down quite a bit. I think that people are probably resigning to the use of “buddy classes” for this purpose; this seems to be the most common substitute.
…ultimately your feedback is at the basis of how we make these choices.
So I began to wonder, have we really resigned ourselves to using these buddy classes? Are they less of a problem for others then they are for me? Am I, perhaps, missing a fairly easy solution to this problem that involves the use of “buddy classes” but solves the issues with that methodology? Or perhaps, are there other features that we want in the language that are just more important to us than this one?
Please let me know if am I missing something or if there are others out there who feel as I do on this feature request. If there are many others like me, perhaps we can put our voices together to, as Mads suggests, let Microsoft know what we need.
Entity Framework Associations on Non-Key Fields
Posted by bsstahl on 2011-02-03 and Filed Under: development
Since I have now, for the second time, run into a problem working with Associations on non-key fields in Entity Framework, it is time for me to take a serious look at the issue.
Consider the model below. There are two entities, a Flight and an Airport. In this scenario, there are two associations between the entities, Flight.DepartFromAirportId –> Airport.Id and Flight.ArriveAtAirportId –> Airport.Id. These associations represent the Departure and Arrival airport of the flight. This model works quite well in Entity Framework 4, making a collection of the arriving and departing flights for each airport available through the navigation properties on the Airport object, and providing a shortcut to the departure and arrival Airport objects for each flight via the navigation properties on the Flight object.
The problems I’ve seen occur when the database was designed a bit differently, as is sometimes the case with legacy systems. Let’s take a look at the second model, below.
Here, we have the same basic model, but instead of the DepartFromAirportId and ArriveAtAirportId foreign-keys on the Flight object, we have DepartFrom and ArriveAt fields which link to the IataCode* property of the Airport.
The Airport entity still has the same key property, but the Flight doesn’t use it to establish the association. The current version of the Entity Framework is not capable of supporting associations in this type of model. If you attempt to establish the association through the designer, you cannot select the proper Principal Key and Dependent Property combination to create the link. If you manually create the association in the XML code, you will get a compiler error.
Fortunately for me, very few of the legacy databases and none of the recently created systems that I work with use this method to create relationships. However, on the rare occasions that this occurs, it can make life much more complicated. Consider the scenario where I need to get a list of flights that are departing from an airport north of 45 degrees in latitude. In the first model, this is easy using LINQ to Entities.
var flights = context.Flights.Where(f => f.DepartureAirport.Latitude > 45);
However, with the second model, since there is no association between the entities, there are no navigation properties that can be followed. Thus the join has to be done in the LINQ to Entities query, making the syntax much more complex.
var flights = context.Flights.Where(
f => context.Airports.Where(a => a.Latitude > 45)
.Contains(context.Airports.Where(a => a.IataCode == f.DepartFrom)
This query finds the flights where the collection of airports with latitude > 45 degrees contains the one airport that has the IataCode matching the flight’s DepartFrom field. As you can see, this query is much more difficult to create and maintain then the one which simply uses the Entity Framework provided navigation property.
There is another solution, but I hate to even mention it since I believe it is likely to cause far more problems down the road then it solves now. That solution, is to manually edit the storage model to fool the Entity Framework into thinking that the properties you wish to use for the association are actually the primary key fields. Of course, were you to make these changes, then later refresh your model from the database, all of the changes would be lost and you would have to start over. While this might not seem like such a horrible thing, remember that it might not be you making those changes, or worse, it is you having to deal with an unworkable model left to you by someone else.
* The Iata Code for an airport is the 3-character code used on your luggage and tickets – PHX, CLT, LAX, ORD, etc.
Entity Framework Inheritance
Posted by bsstahl on 2011-01-20 and Filed Under: development
Alex D. James posted a great little primer on Entity Framework inheritance strategies and when to use each.
His post can be found here.