I am using EF 4.3 in an ASP.NET WebForms application. I've started with model first approach with context object of type ObjectContext and POCO code generator (via T4).
At the beginning the Context was created at the beginning of every service method. While working on performance I decided to switch to context per web request. Unfortunately I have encountered an issue with Table-per-Type inheritance. I have two entities: Offer and OfferEdit. They are in a one to one relationship, and both share the same primary key. Basically an OfferEdit (OfferEdits table) is created once an Offer is being edited.
I query the context for a particular Offer entity more then once during web request. The error I get trying to execute:
var offer = Context.Offer.Where(o => o.Id == offerId).FirstOrDefault()
when this offer is already loaded to Context.Offer.EntitySet is
All objects in the EntitySet 'RuchEntities.Offer' must have unique primary keys.
However, an instance of type 'Ruch.Data.Model.OfferEdit' and an instance of type'Ruch.Data.Model.Offer' both have the same primary key
value,'EntitySet=Offer;Id=4139'.
Will appreciate all advice.
Sounds like you are misusing TPT inheritance. To make it clear EF inheritance works exactly same way as in .NET - the entity can be either of type Offer or OfferEdit. You can convert OfferEdit to Offer but it is still OfferEdit. It can never be of both types which means you can never have Offer entity with Id same as OfferEdit entity because same key cannot be used by two entity instances. You also never can change instance of Offer to OfferEdit because .NET doesn't allow you changing type of existing instance.
Related
Background
With ef core code first approach, validation is robust and simple: https://learn.microsoft.com/en-us/aspnet/core/tutorials/first-mvc-app/validation
With the database first approach, it seems like any validation is happening behind the scenes by the database when dbcontext.SaveChanges(); is called. What's worse, these exceptions are nebulous and entirely unhelpful, for example, SqlException: String or binary data would be truncated can be thrown if any of the string properties of any of the entities have too many chars (ours is a legacy app riddled with char(10) and such), or even if a key that is a string is left null.
Question
I want to know if there is any reasonable or accepted way of enforcing the validation. I've found this question which might help debugging, but I would like to enforce the constraints in code
Is there any better method than changing every auto property to one that throws if it's constraints aren't met?
EntityFramework Core does not enforce any validation at all. The validation rules you see in the example are enforced by MVC and not EF. One of the main reason for EF Core to remove validation check was that only. Validation are run in UI and then in EF and then again in database which is just redundant. Hence client side validation is left to the front-end (MVC in this case) and server side is done by database engine.
When you use database first approach, EF core does not generate any annotation for validation because it does not reason about them anyway. That means you would get only server side validation which means error during SaveChanges.
The only way to enforce constraint in the code (client side) is to write those annotations so that MVC can enforce them or write custom code to deal with it. The whole validation mechanism is transparent to EF.
I ended up going with a psuedo extension to the generator tooling. Since the DBContext is a partial class, I made a new class that has a main
public partial class DBContext{
public static void Main(string[]args){
DBContext context = new DBContext();
var modelbuilder = new Microsoft.EntityFrameworkCore.ModelBuilder(new Microsoft.EntityFrameworkCore.Metadata.Conventions.ConventionSet());
context.OnModelCreating(modelbuilder);
IMutableModel model=modelbuilder.Model;
from there I used Linq to transform the various info about each entity's properties and the annotations on them into List<KeyValuePair<string,List<KeyValuePair<Regex,string>>>> where the first pair's key is the entity name, and the value is a list of find and replace pairs to edit the code that had already been generated with the corresponding validation, one per property. Then all I had to do was abuse the fact that the tooling generates the classes in <className>.cs files, and iterate over my list, executing the replacements for each entity source code file.
I'd have preferred doing something a little less hacky, because I'm relying on format that the ef tooling outputs, but it works
From a couple of articles I have found online
http://typecastexception.com/post/2013/10/27/Configuring-Db-Connection-and-Code-First-Migration-for-Identity-Accounts-in-ASPNET-MVC-5-and-Visual-Studio-2013.aspx
http://www.codeproject.com/Articles/790720/ASP-NET-Identity-Customizing-Users-and-Roles
I have seen it is very simple to extend the ApplicationUser class in MVC 5/Identity 2.0. It basically requires adding of property to that class and all dependent views/viewmodels etc to implement the new functionality. The only question I have remaining is due to the fact that these articles all give you examples in regards to a code first perspective. How would extending the Applicationser class work with a database first perspective?
Here is what I imagine.
1.) Change the connection string to your production database. (In my case SQL Azure)
2.) Create the tables that are normally automatically created by identity 2.0 in SQL Azure.
3.) Fill those tables with the default properties and types.
4.) Add custom properties to the AspNetUsers table. (E.G. City, Zip, etc)
5.) Add those properties to the actual ApplicationUser class
6.) Update dependent views, controllers, viewmodels etc.
Is there a more simple way in doing this?
No, there is no other way to extend ApplicationUser. Code-First is pretty much the same, only adding properties first, create migration, run migration, update your controllers/views.
I am trying to use Entity Framework 4.0 for an asp .net application. As of now, it will be old style code behind files and without unit testing but in the future I may use MVP and unit testing but as of now, it is not a concern for me. I am using Database First approach. Here is a model ( I could not post image as I need reputation to post image)
Table: Application (ApplicationID, Name, Hidden)
Table: User (UserID, ApplicationID, Username, IsActive)
Table: Role (RoleID, ApplicationID, Name)
Table: UserRole (UserRoleID, RoleID, UserID)
I have been reading a lot about Entity Framework and how to use it but still could not get a very basic idea about some stuff. Where do I write a code like this for Application, User, Role, UserRole etc?
public List<Application> GetAllUnhiddenApplications()
{
List<Application> applist = null;
using (CustomAppsPortalEntities ctx = new CustomAppsPortalEntities())
{
applist = (from app in ctx.Applications
where app.Hidden == false
orderby app.Name
select app).ToList();
}
return applist;
}
I have separated Context and Entities in separate projects Project.Data and Project.Entities respectively. My question is if above code belongs to BLL (class name ApplicationBLL) or DLL (ApplicationDLL)? From past 2 days, I have been searching lots of SO questions, blogs, tutorials and different people have different approach. Here is my dilemma.
If I put the code in Data layer, then in the business layer, I have to create a "pass through" function like ApplicationBLL.GetAllUnhiddenApplications which will return ApplidationDLL.GetAllUnhiddenApplications. I have to repeat it for all the queries and basically whole BLL will eventually become "pass through" layer for DLL. Can you give me a concrete example of what Business layer will be used for in reference to above schema?
If I put the code in Business layer, then linq will exist in Business layer which eventually will be converted to SQL by Entity Framework so it is like exposing query logic to Business Layer.
Our Environment
Our environment is fast paced and want to complete this project as soon as possible with the moderately proper approach where there is a separate layer but in the future when we find time, we may refactor the code and make it really robust but it is not a concern as of now but if the time permits, we want to implement best practices right now versus refactoring code in the future.
The above code would typically be in the BL layer. Using linq in your BL layer is fine because your linq queries are still data persistence ignorant. From linq queries perspective, it's querying objects from entity framework.
What you might be missing is a "repository pattern" and "unit of work patter". The repository pattern acts as an interface to entity framework. It allows you to interact with EF objects like in-memory collections. Typically I keep all repositories in one project and reference accordingly. To give you an example, Microsoft Spain provides a n-tierd example,
http://microsoftnlayerapp.codeplex.com/
It's very over engineered, but I believe it will give you what your looking for.
Many people argue that EF IS the DLL.
Typically, I set my projects up something like this...
D ---> Presentation Layers (MVC, WCF, WinForms, etc)
A |
T V
A ---> Business Logic Layer
|
M V
O ---> Entity Layer / DLL
D
E
L
The Data Models project is really just a collection of POCO's that can be used in any of the other projects.
The Entity Layer is your EDMX file and Context.
It should be fine to access the context in the Entity/DLL layer, since .Net has abstracted everything out for you.
If you think about it, the whole reason to abstract out a DLL layer is so that you can change databases without having to change the BLL. With EF, you can change a database in 1 step and everything should still work.... as long as your schema stays the same.
I have a requirement to keep a history of values of some fields in an EF4 ASP.NET MVC3 application. This just needs to be a log file of sorts, log the user, datetime, tablename, fieldname, oldvalue, newvalue.
Although it would be pretty easy to code this in various save routines, I'm wondering if I can get global coverage by wiring it into some sort of dataannotation, so that I can perhaps declare
[KeepHistory()]
public string Surname { get; set; }
in my partial class (I'm using POCO but generated from a T4 template).
So Questions
1) Is this a bad idea ? I'm basically proposing to side-effect changes to an entity, not directly referenced by the code, as a result of an annotation.
2) Can it be done ? Will I have access to the right context to tie up with my unit of work so that changes get saved or dropped with the context save?
3) Is there a better way?
4) If you suggest I do this, any pointers would be appreciated - everything I've read is for validation, which may not be the best starting point.
Actually, validation might be a good starting point. Since an attribute does not know about which property or class it was assigned to, but a validation-attribute gets called by the validation framework with all the necessary informátion. If you implement the System.ComponentModel.DataAnnotations.ValidationAttribute class you can override the IsValid(object, ValidationContext) method, which gives you the actual value of the property, the name of the property and the container.
This might take a lot of work, since you need to get to the currently logged-in user etc. I'm guessing that the .NET implementation provides some sort of caching for the specific attributes on an entity type, which would be a pain to implement by yourself.
Another way, would be to use the ObjectStateManager exposed by your EF ObjectContext, which can provide you with the ObjectStateEntry-objects for all entities of a given state. See the
ObjectStateManager.GetObjectStateEntries(EntityState) method, for more information about how to call it (and when). The ObjectStateEntry actually contains a record of the original and current-values, which can be compared to find any changes made within the lifetime of the current ObjectContext.
You might consider using the ObjectStateManager to inject your custom logging behavior, while this behavior decides based on property-attributes which change should be logged.
I have an existing web application that uses EF and POCO objects. I want to improve the client experience by exposing some of my objects through WCF(JSON). I have this working fine but where I am unsure is how to handle derived objects(not sure if that is the correct term) or IEnumerable anonymous objects if you will.
Let's say I have 3 tables structured like so:
Templates
ID
Template
Groups
ID
Group
Instances
ID
TemplateID
GroupID
This is obviously a one-to-many type relationship. I have my navigation properties setup correctly and getting strongly typed object properties works great. However, how do I send serialized anonymous type object(s) over the wire. Like an object that sends all instances that are equal to groupid=1 and include the names of the template and the object.
Am I missing something or do I have to create another class object for WCF that would look like this:
WCF Object
InstanceID
TemplateID
TemplateName
GroupID
GroupName
I guess I could alter my tables to account for this but that seems wrong too. I know that IEnumerable objects can't be serialized and I know that throw away objects are probably not the way to go either. I want to do this the right way but I am not sure how to go about it.
Your suggestions are appreciated.
Regards
Based on what you're doing, I'd suggest looking at OData with WCF Data Services. You state that you want to be able to send all instances where the groupid=1 - OData is great at this type of filtering.
If you're want to stick with your current approach and not use OData, then my first question is why are you sending back anonymous types at all? You can do what you are seeking (all instances with a groupid=1) without sending back an anonymous type. In your select clause you just create new instances of your concrete objects rather than newing up anonymous types. If your query is really just filtering and not executing any meaningful projection with the selct to anonymous type, then I don't see any reason to send back your anonymous type at all.