I'm currently trying to migrate a project to EF4 POCOs in order to get rid of EntityObject in my business logic and ran into an issue with duplicate table names. The DAL has access to 3 different databases and there are 3 .edmx files, one for each database.
However, some tables in those databases share the same name, e.g. DB1.CUSTOMER and DB2.CUSTOMER. I managed to have the related entities created in different namespaces (one namespace for each database) like MyApp.Db1.CUSTOMER and MyApp.Db2.CUSTOMER, the trouble is EF can't decide which one to pick and claims there was an ambiguity which isn't actually the case.
Is there any way of mapping Entities to their respective POCOs manually or any sort of workaround? This is EF 4.2.
EF doesn't use namespace when recognizing entity type. The name of class is matched directly with name of entity in your model diagram (EDMX). So the workaround is using different names in different models which will also make your code much better readable.
Related
I have a domain model architecture in which my domain/business objects were created based on the problem domain and independent of any knowledge of the physical data model or persistence structures. So far I'm on track because it's perfectly acceptable and often the case that there is an impedance mismatch between the domain model and the data model. A DBA created the database for getting the data they required, but it does not encapsulate the applications entire domain model or design.
The result - I have my own set of domain model objects. However all of the fields that need to be persisted do exist somewhere or another within my domain model, but not necessarily in the shape that my auto generated .edmx POCO entities have them. So I have all the data, it's just not in the perfect shape exactly like the tables in which auto generated POCO entities are created from.
I have seen a few posts on this topic like converting POCO entity to business entity and Entity Framework 4 with Existing Domain Model that make statements like the following:
"Create the entities in your entity data model with the same names as
your domain classes. The entity properties should also have the same
names and types as in the domain classes"
What!? No way, why should I have to make my domain model be reshaped to POCOs that are modeled exactly after the data model / table structure in the database? For example - in my case of having 5 given properties, 2 might be in class 'A' and 3 in class 'B', whereas a auto generated POCO class has all 5 in its own class 'A'.
This is the entire point, I want separation of my object model and data model but yet still use an ORM like EF 5.0 to map in between them. I do not want to have to create and shape classes and properties named as such in the data model.
Right now my .edmx in EF 5.0 is generating the POCO classes for me, but my question is how to dissolve these and rewire everything to my domain objects that contain all this data but just in a different shape?
By the way any solution proposed using a Code First approach is not an option so please do not offer this. I need some guidance or a tutorial (best) using EF5 (if possible because EF4 examples are always inheriting POCOs from ObjectContext) with wiring up my own business objects to the .edmx.
Any help or guidance is appreciated, thanks!
This sounds like exactly the use case of Entity Framework. I am making a few assumptions here. First that when you make this statement:
"I have a domain model architecture in which my domain/business objects were created based on the problem domain and independent of any knowledge of the physical data model or persistence structures."
That you mean this domain was created in the EF designer? But then you say:
"However all of the fields that need to be persisted do exist somewhere or another within my domain model, but not necessarily in the shape that my auto generated .edmx POCO entities have them."
This sounds to me like my first assumption is incorrect.
Next, you dismiss code first? If your domain model/business objects are code based and you want to persist them to a relational database, that is exactly the use case for code first. You have the code, now you need to create your DbContext and map it to your physical model.
However you dismiss that... so some thoughts:
If you have a domain model of code based business objects and you have an EDMX that is used for other things I think you would want to create a repository layer that uses something like auto mapper or manual projections to query your Entities and return your business objects.
If you have a domain model of code based business objects and you have an EDMX that is not used for other things other than persisting your business objects I would say that you need to express your domain in an EDMX and then map it onto your existing database. This is really the use case for an ORM. Having two domain models and mapping from one model to the other where one model matches your domain and one matches your database is adding an extra un-needed layer of plumbing.
The latter approach above is what is called "Model First" in EF parlance. There are several articles written about it although the bulk of them just generate the db from the model. You would not do that step, rather you would map your entities onto your existing database.
The basic steps for this are to "update from the database" not selecting any of the db objects (or entities would be created). Or, you can take your exiting .edmx in the designer (which is sounds like you have) and modify the entities to match your business domain. Or just delete all the entities in your EDMX model, create your entities as you want them, and then map them all.
Here is a jing I made where I use the EF Designer to bring in the model store (the only way to do this is to allow it to generate entities) and then delete the entities allowing the Store information to stay by clicking NO when it asks if you want to delete the table info.
http://screencast.com/t/8eiPg2kcp
I didn't add the POCO generator to this, but if I did it would generate the Entities in the designer as POCO classes.
The statement quoted above is not suggesting that you rewrite your domain objects to match your pocos, it is suggesting that you update the edmx to match your domain model.
In your example you could create an entity in your edmx that maps all 5 properties from both tables and EF will manage the mapping to and from the single generated Poco onto your tables.
Of course this means that you then have duplicate domain objects and pocos, meaning you would either have to manually convert your domain objects to pocos when interacting with EF,
or you could define your domain data objects as interfaces and provide partial implementations of the pocos that essentially identify each poco as being a concrete implementation of a domain object.
There are probably several other ways to skin this particular cat, but I don't think that you can provide predefined c# objects for use in an edmx.
One approach might be to select into a ViewModel (suited to your particular business logic) and automatically map some data from the context into it like so https://stackoverflow.com/a/8588843/201648. This uses AutoMapper to map entity properties from an EF context into a ViewModel. This won't do everything for you, but it might make life a bit easier. If you're unhappy with the way this occurs automatically, you can configure AutoMapper to do things a bit differently (see Projection) - https://github.com/AutoMapper/AutoMapper/wiki/Projection
You might know this already, but its also possible to automatically generate POCOs from your EDMX using t4 - http://visualstudiogallery.msdn.microsoft.com/72a60b14-1581-4b9b-89f2-846072eff19d. If you define the templates to generate partial classes, you can then have another partial class with your custom properties for that POCO. That way you can have most properties automatically populated, but have other custom properties which you populate with custom rules from your context/repository. This takes a lot of the monotony out of generating these, and you can then focus on reshaping the data using the above technique.
If you're seriously unhappy with both, you could always map a stored procedure to get the exact field names that you want automatically without needing to stuff around. This will of course affect how you work with the data, but I have done it before for optimisation purposes/where a procedure already existed that did exactly what I wanted. See http://msdn.microsoft.com/en-us/data/gg699321.aspx
Im currently working in a team that uses EF as the ORM of choice.
We have a common project that contains many EDMX files.
The reason for this is to keep the EDMX files small and manageable while also allowing them to focus on a conceptual set of tables on the database.
Eg
Orders.edmx
Users.edmx
Trades.edmx
These all point to a different set of tables on the same db.
I now need to add the user table to the Trade.edmx file. Since the user table is already in the user.edmx file, this creates the same User type twice under a different namespace which means I would need 2 UserRepository objects.
Common.data.trade.User
Common.data.users.User
Is there a way of avoiding 2 repository objects for the same table?
Any suggestions would be greatly appreciated
If you are using POCO generator you can update template for Trades.edmx to not generate new User class and its context template to use User class from Users namespace. EF matches POCO classes with entities in designer only by the class name (namespace is omitted) so it will work.
The disadvantage is that you have User entity in two mapping files and you must update it in both files or your application throw exception at runtime.
The reason for this problem is your architecture - at the beginning you wanted separated models but know you want to combine entities from different models. Those are contradicting requirements. Either use separated model where Trade knows only userID without any navigation property (like if it is defined in another database) or move all entities to single EDMX to support your new requirements.
I understand that, when working with POCO entities, you should work against your model (POCO Entities). Also I supose that part of the benefits of programming against models like those should provide benefits like defining classes that don't match exactly what you see in the db.
However, there are simple operations that I don't know how to do and that I assume they should be possible. For example, in some scenarios it can be useful to change the name of one column (atribute in the entity). Also I would like to know if it's possible to generate POCO models that only represents some fields of the table that supports the object in the db.
Is there any documentation about this kind of operations?
¡Thanks a lot!
POCO entity is just mapped class. The model in your question means mapping. The point of mapping is to define map between class and database table including mapping between properties and columns. So you can have different property and column names as long as it is correctly configured in mapping.
So if you are using EDMX file (designer) for generating the mapping you can simply change the name of property or entity and it will be reflected in your generated POCO entity. Also EDMX file will correctly update mapping. If you are using code first you must manually define mapping either through data annotations or through fluent API.
Entity should represent single data structure persisted to the database. Because of this each table can be mapped only once. Moreover EDMX designer demands that each non-nullable column without default value must be mapped to the entity. POCO generator is not tool for generating your different data views. What you are looking for is called projection. There are ways how to include mapped projections in EDMX file (DefiningQuery and QueryView) but both requires manual modifications of EDMX file and the first one also requires manual maintenance of EDMX file.
If you need to remove some properties from entity just to improve some query or because you don't need all data for some operation you can always use projection to anonymous or custom class directly in the query.
var query = from x in context.XEntities
select new XView
{
A = x.A,
B = x.B
};
POCO generator is only tool for generating classes for mapped entities and projections not for generating all data related classes you will ever need.
Trying to understand Entity Framework. My approach is database first. However I would like to define other entites in the model that is closer to my business objects. I guess I could write queries in the db and include them in the model. But I would also like to define entirely new entities in the model though they would be based on underlying tables in the db. How do I do that - does anyone know a tutorial?
Regards
Bjørn
db Oldtimer, EF Newbie
Database first means that you have existing database and you can either create model by updating from database or manually. You can use wizard to create initial model and modify it manually to define new entities but you must not use update from database any more or some of your changes will be deleted. Also your custom modifications must follow EF mapping rules (for example it is not directly possible to map multiple entities to the same table except some more advanced mapping scenarios like splitting and inheritance) and some of them (custom queries) must be done directly in EDMX source (XML) because designer doesn't support them - this requires more complex knowledge of EF mapping and it will be definitely hard for newbie.
You can check specification of that XML. For entities mapped to custom queries you will have to use DefiningQuery element in SSDL part of EDMX.
I'm a newbie to ADO.Net Entity framework 4. I have a set of pocos which I need to map to a legacy database. The problem is that the db field names are different to the poco property names. eg. db field name = 'cusID' and poco property = 'CustomerID'.
What is the best way to map these?
This is exactly the problem EF mapping is designed to solve.
Your POCO class need to match your 'conceptual model'... Not your 'data model'.
If in EF you build your model from the database you simply need to rename your entity properties. Doing this changes the conceptual model - to match your POCO classes - but leaves the storage model unchanged, and sets up the appropriate mappings.
Entity Framework CTP4 has a new feature called Code First that allows you to map POCO property members to database table column names. This blog article may be what you are looking for,
http://theminimalistdeveloper.com/2010/07/28/how-to-map-pocos-to-existing-databases-in-entity-framework-4-0-code-first-and-asp-net-mvc-2/
Additionally, EF CTP 5 - which will be released in the next few weeks - has a better API to fluently configure your own conventions to map your POCO domain classes to existing database structures.
Hope this helps.
Update Here is the new article that discusses how to achieve this in EF4 CTP5