So I was reading about Entity Framework and based on my agile development scenario I decided to go with POCO objects.
But now I'm having some extra problems I don't know how to get away with.
I'm working with RIA services and Silverlight so when I'm going to Save an object of the server side I have to attach the object to an ObjectContext. The thing is that I must then change the ObjectState to Added or Modified.
So my question is what's the best approach to really know what state to change it to. I saw in Julia Lerman's book that she uses a State attribute in her POCO objects and she takes care managing that state on the client side before sending the object to the server. That state then is used to change the real EntitySate once attached.
I've also seen other samples where the Insert implementation checks on the Key of the Entity (object) to know whether it is new or not. For example, if ProjectId in my Project entity is 0 (zero) I know it has to be a new object.
To be honest I don't like any of those approaches because in both cases my developers have to do some extra-work to actually save the object.
I'd like the know pros and cons of both solutions and hopefully a new (better) solution I'm still not seing.
You can still have self tracking entities and poco. In visual studio if you search the community templates there is a self tracking poco template. this is what you want to use. If you can find the template look for your entities using Ientitywithobjecttracker.
http://msdn.microsoft.com/en-us/library/dd456848.aspx
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We are currently rewriting an existing internal ASP.NET Web Forms application. Our application consists of a Web Api back end which uses Entity Framework 6 for data access and an front end which uses AngularJS.
We have an existing large database that I've created EF models using the Code-First Using Existing Database method and we are using data transfer object classes as inputs/outputs to our API methods so we aren't directly exposing our model classes. So basically, I'm trying to become proficient with EF, Web Api and AngularJS all at the same time. For the most part I'm fairly comfortable with the latter two, but for EF I haven't completely gotten comfortable with. I've watched a lot of the videos on Microsoft Virtual Academy but this is the first time I've had some hands-on experience with it.
We've been working on this application for a few months and so far we've only had to work with CRUD operations on our entities (POCO DTO's) which are flat objects with simple properties. However, we've finally come across some situations where we need to deal not only with our classes, but properties which are classes themselves; a parent-child relationship.
Therefore, I have the following questions:
I see that when we have a proper foreign key relationship in our DB, that virtual properties are created in EF, which from what I recall are to support lazy-loading. However, lazy-loading isn't really feasible in this environment where we are using web services (Web Api). Our object model does allow for some really large hierarchy of classes where a fully populated object and its children would mean a large amount of data would be passed around when that really isn't necessary, so in most cases a first level object is all we need. In some cases however, we do want to populate child classes, so my question is how do we do that, and where do we do that? I've looked at the automatically-generated code in the DB Context but we have also used scaffolded code to create our controllers. Which place do we need to do this? I've seen code samples showing how do to this but it hasn't said specifically where this code lies. It appears to be within a controller but I could be wrong.
If we do allow for 2- or more level hierarchy of objects, does EF automatically handle operations (updates, deletes, etc.) -- for example, if we have a "Company" object which has a collection of "Customer" objects, and we delete the "Company" object, do the related "Customer" objects get deleted too? Also, is a multi-step operation like that automatically performed within a transaction or do we need to explicitly set that up?
If I modify a model class or the DB context, seeing as this code is automatically-generated, that's generally bad practice as my changes could be overwritten, so I am assuming the controller code is where I want to make my changes. I am aware of database migrations but I have no experience with them and I am sure I'll need to use them at some point because I am fairly confident that our database may not have all the foreign key relationships necessary for EF to do everything we need at the moment.
I know this is a long post, but if anyone can give some guidance on how to do some of these things because it's not only me that's having to deal with this but I have two other developers on my team who are working on this project and we are all as inexperienced with this as the others are. Thanks
For the purpose of sending data across a web service, I'd suggest creating a DTO to hold the data you want to send and mapping your entities to the DTO instead of trying to send the entities themselves in your payload. It also protects your API from changes to your entity.
Cascading deletes are configurable, iirc, but I'm not 100% sure what the default is. Transactions are generally not implicit, so you will want to use those where you require them.
Not exactly sure what you are asking here. In general, how your entities/tables change depends on if you are using database-first or code-first. If you are using database-first (you will have a .edmx file in your solution that has the model matching your schema), you just update the SQL directly and update your entity model via the .edmx. If you use code-first, you will change the entities how you want them and run a database migration to update your database to match.
MSDN article about code-first migration: https://msdn.microsoft.com/en-us/data/jj591621.aspx
Can anyone direct me to a good strategy for implementing change tracking in my Entity Framework model?
I have around 20 entities to track changes on (accessed via facades / unit of work) and I need to be able to display who changed what when on displaying the record in the UI.
I know there's Context.OnSavingChanges (or whatever it's called) but I'd probably want to access the changes in queries like context.MyEntity.ChangeLog
Must I create a ChangeLog entity, add associations to all the entities or is there a better via via savingchanges?
Richard
P.s. Have a great weekend!
Entity framework is ORM = API responsible for persistence and loading from database. What you persist or load is completely up to you so if you want change tracking you must to code it.
The most common approach is indeed using OnSavingChanges or overriding SaveChanges because you are usually saving changed executed by single user.
An old question but for anyone looking for auditing changes on EF >= 6 or EF Core, I worked on an open source library Audit.EntityFramework you could try.
See FrameLog, which is an open source library I wrote for this purpose. You call it from SaveChanges and it deals with the rest, including giving you a strongly-typed API for querying the logs.
I have an architectural question about EF and WCF.
We are developing a three-tier application using Entity Framework (with an Oracle database), and a GUI based on WPF. The GUI communicates with the server through WCF.
Our data model is quite complex (more than a hundred tables), with lots of relations. We are currently using the default EF code generation template, and we are having a lot of trouble with tracking the state of our entities.
The user interfaces on the client are also fairly complex, sometimes an object graph with more than 50 objects are sent down to a single user interface, with several layers of aggregation between the entities. It is an important goal to be able to easily decide in the BLL layer, which of the objects have been modified on the client, and which objects have been newly created.
What would be the clearest approach to manage entities and entity states between the two layers? Self tracking entities? What are the most common pitfalls in this scenario?
Could those who have used STEs in a real production environment tell their experiences?
STEs are supposed to solve this scenario but they are not silver bullet. I have never used them in real project (I don't like them) but I spent some time playing with them. The main pitfalls I found are:
Coupling your data layer with your client application - you must share entity assembly between projects (it also means it is .NET only solution but it should not be a problem in your case)
Large data transfers - you pass 50 entities to clients, client change single entity and you will pass 50 entities back. It will require some fighting with STEs to avoid passing unnecessary data
Unnecessary updates to database - normally when EF works with attached entities it track changes on property level but with STEs it track changes on entity level. So if user modify single property in entity with 100 properties it will generate update with setting all of them. It will require modifying template and adding property level change tracking to avoid this.
Client application should use STEs directly (binding STEs to UI) to get most of its self tracking ability. Otherwise you will have to implement code which will move data from UI back to self tracking entity and modify its state.
They are not proxied = they don't support lazy loading (in case of WCF service it is good behavior)
I described today the way to solve this without STEs. There is also related question about tracking over web services (check #Richard's answer and provided links).
We have developed a layered application with STE's. A user interface layer with ASP.NET and ModelViewPresenter, a business layer, a WCF service layer and the data layer with Entity Framework.
When I first read about STE's the documentation said that they are easier then using custom DTO's. They should be the 'quick and easy way' and that only on really big projects you should use hand written DTO's.
But we've run in a lot of problems using STE's. One of the main problems is that if your entities come from multiple service calls (for example in a master detail view) and so from different contexts you will run into problems when composing the graphs on the server and trying to save them. So our server function still have to check manually which data has changed and then recompose the object graph on the server. A lot has been written about this topic but it's still not easy to fix.
Another problem we ran into was that the STE's wouldn't work without WCF. The change tracking is activated when the entities are serialized. We've originally designed an architecture where WCF could be disabled and the service calls would just be in process (this was a requirement for our unit tests, which would run a lot faster without wcf and be easier to setup). It turned out that STE's are not the right choice for this.
I've also noticed that developers sometimes included a lot of data in their query and just send it to the client instead of really thinking about which data they needed.
After this project we've decided to use custom DTO's with automapper from server to client and use the POCO template in our data layer in a new project.
So since you already state that your project is big I would opt for custom DTO's and service functions that are a specifically created for one goal instead of 'Update(Person person)' functions that send a lot of data
Hope this helps :)
We have a Silverlight 4 client connecting to RIA services. It's based on the standard "Business Application" Silverlight application in VS 2010. The objects we send to the client over RIA services are EF 4 entities that are POCO objects generated from our edmx by T4. Our RIA service is a LinqToEntitiesDomainService<> of our linq repository.
We have two Entities that share similar structure but are unrelated. Both are both have navigation property that represents a single instances of another entity. Both are retrieved using methods marked [Query]. For one entity the navigation property is always correctly populated when we try and access its value; for the other it is never populated, it always remains null (well it seems to hold an EntityRef<> object that points to a null entity). We have verified the relations in the edmx and the generated code on the client side, both seem to share the same structure, so we don’t understand why this difference in behavior is happening. Can anyone shed some light on the subject?
Many thanks,
Robert
Are you using the "[Include]" attribute and "Include" functions in one of your entities / domain services methods and not the other one? If so, this answer to a similar question might help you: If you create a DomainService, exposing an entity, can you access aggregate entities?
Cannot give any definite answer, but you could try by checking these things:
Is there any data in the database for the object that is null
Are the query parameters correct
Do you have a test on the server side to see that the data is available
Is there an attribute missing on one of the objects
I've been using the entity framework in combination with the self tracking entity code generation templates for my latest silverlight to WCF application. It's the first time I've used the entity framework in a real project and my hope was that I would save myself a lot of time and effort by being able to automatically update the whole data access layer of my project when my database schema changed.
Happily I've found that to be the case, updating my database schema by adding a new table, changing column names, adding new columns etc. etc. can be propagated to my business object classes by using the update from database option on the entity framework model.
Where I'm hurting is the CRUD operations within my WCF service in response to actions on my Silverlight client. I use the same self tracking entity framework business objects in my Silverlight app but I find I'm continually having to fight against problems such as foreign key associations not being handled correctly when updating an object or the change tracker getting confused about the state of an object at the Silverlight end and the data access operation within the WCF layer throwing a wobbly.
It's got to a point where I have now spent more time dealing with this quirks than I have on my previous project where I used Linq-to-SQL as the starting point for rolling my own business objects.
Is it just me being hopeless or is the self tracking entities approach something that should be avoided until it's more mature?
What version of self tracking entities are you using?
I'm using the .Net 4.0 version together with visual studio 2010. All CRUD operations work fine, also operation with FK.
I had problems in VS 2008 with FK but that's gone in VS 2010 with .Net 4.0.
If you want, I can provide you some samples.
Greetings
Since STE entity does not support lazy loading you should use Include on the server side include related properties. There is no way to include all related navigation properties. You have to explicitly include the properties. for instance
//server side
customer.Include("Orders.OrderDetails").Include("Address")