Combine Code First & Database First In Single Mode

问题:

Is there a way to combine code-first and database-first in the same context? We are running into massive development-time performance problems when editing the EDMX file (it takes 1.5 minutes to save). I've moved our non-insert/update/delete UDFs/stored procs to some custom T4 templates that automatically generate model-first code, but I can't seem to get OnModelCreating to be called when EDMX is involved.

Other things we've considered, but won't work for one reason or another:

1. We can't (reasonably) separate our code to multiple contexts as there is a lot of overlap in our entity relationships. It also seems like quite a people who have gone this route regret it.

2. We tried having 2 different contexts, but there are quite a few joins between Entities & UDFs. This may be our last hope, but I'd REALLY like to avoid it.

3. We can't switch to Dapper since we have unfortunately made heavy use of IQueryable.

4. We tried to go completely to Code-First, but there are features that we are using in EDMX that aren't supported (mostly related to insert/update/delete stored procedure mapping).

回答1:

Take a look at the following link. I answered another question in a similar fashion:
How to use Repository pattern using Database first approach in entity framework

As I mentioned in that post, I would personally try to switch to a Code First approach and get rid of the EDMX files as it is already deprecated and most importantly, the maintenance effort is considerable and much more complex compared with the Code First approach.

It is not that hard switching to Code First from a Model First approach. Some steps and images down below:

1. Display all files at the project level and expand the EDMX file. You will notice that the EDMX file has a .TT file which will have several files nested, the Model Context and POCO clases between them as .cs or .vb classes (depending on the language you are using). See image down below:
   
2. Unload the project, right click and then edit.
3. See the image below, notice the dependencies between the context and the TT file
   
4. Remove the dependencies, the xml element should look like the image below:
   
5. Repeat the procedure for the Model classes (The ones with the model definition)
6. Reload your project, remove the EDMX file(s)
7. You will probably need to do some tweeks and update names/references.

I did this a few times in the past and it worked flawlessly on production. You can also look for tools that do this conversion for you.

This might be a good opportunity for you to rethink the architecture as well.

BTW: Bullet point 4 shouldn't be a show stopper for you. You can map/use Stored Procedures via EF. Look at the following link:
How to call Stored Procedure in Entity Framework 6 (Code-First)?

回答2:

It also seems like quite a people who have gone this route [multiple contexts] regret it.

I'm not one of them.

Your core problem is a context that gets too large. So break it up. I know that inevitably there will be entities that should be shared among several contexts, which may give rise to duplicate class names. An easy way to solve this is to rename the classes into their context-specific names.

For example, I have an ApplicationUser table (who hasn't) that maps to a class with the same name in the main context, but to a class AuthorizationUser in my AuthorizationContext, or ReportingUser in a ReportingContext. This isn't a problem at all. Most use cases revolve around one context type anyway, so it's impossible to get confused.

I even have specialized contexts that work on the same data as other contexts, but in a more economical way. For example, a context that doesn't map to calculated columns in the database, so there are no reads after inserts and updates (apart from identity values).

So I'd recommend to go for it, because ...

Is there a way to combine code-first and database-first in the same context?

No, there isn't. Both approaches have different ways of building the DbModel (containing the store model, the class model, and the mappings between both). In a generated DbContext you even see that an UnintentionalCodeFirstException is thrown, to drive home that you're not supposed to use that method.

mostly related to insert/update/delete stored procedure mapping

As said in another answer, mapping CUD actions to stored procedures is supported in EF6 code-first.

回答3:

I got here from a link in your comment on a different question, where you asked:

you mentioned that code-first & database-first is "technically possible" could you explain how to accomplish that?

First, the context of the other question was completely different. The OP there was asking if it was possible to use both database-first and code-first methodologies in the same project, but importantly, not necessarily the same context. My saying that it was "technically possible" applies to the former, not the latter. There is absolutely no way to utilize both code-first and database-first in the same context. Actually, to be a bit more specific, let's say there's no way to utilize an existing database and also migrate that same database with new entities.

The terminology gets a bit confused here due to some unfortunate naming by Microsoft when EF was being developed. Originally, you had just Model-first and Database-first. Both utilized EDMX. The only difference was that Model-first would let you design your entities and create a database from that, while Database-first took an existing database and created entities from that.

With EF 4.1, Code-first was introduced, which discarded EDMX entirely and let you work with POCOs (plain old class objects). However, despite the name, Code-first can and always has been able to work with an existing database or create a new one. Code-first, then is really Model-first and Database-first, combined, minus the horrid EDMX. Recently, the EF team has finally taken it a step further and deprecated EDMX entirely, including both the Model-first and Database-first methodologies. It is not recommended to continue to use either one at this point, and you can expect EDMX support to be dropped entirely in future versions of Visual Studio.

With all that said, let's go with the facts. You cannot both have an existing database and a EF-managed database in a single context. You would at least need two: one for your existing tables and one for those managed by EF. More to the point, these two contexts must reference different databases. If there are any existing tables in an EF-managed database, EF will attempt to remove them. Long and short, you have to segregate your EF-managed stuff from your externally managed stuff, which means you can't create foreign keys between entities in one context and another.

Your only real option here is to just do everything "database-first". In other words, you'll have to just treat your database as existing and manually create new tables, alter columns, etc. without relying on EF migrations at all. In this regard, you should also go ahead and dump the EDMX. Generate all your entities as POCOs and simply disable the database initializer in your context. In other words, Code-first with an existing database. I have additional information, if you need it.

回答4:

Thank you to everyone for the well thought out and thorough answers.

Many of these other answers assume that the stored procedure mappings in EF Code-First work the same, but they do not. I'm a bit fuzzy on this as it's been about 6 months since I looked at it, but I believe as of EF 6.3 code first stored procedures require that you pass every column from your entity to your insert/update stored procedure and that you only pass the key column(s) to your delete procedure. There isn't an option to pick and choose which columns you can pass. We have a requirement to maintain who deleted a record so we have to pass some additional information besides just a simple key.

That being said, what I ended up doing was using a T4 template to automatically generate my EDMX/Context/Model files from the database (with some additional meta-data). This took our developer time experience down from 1.5 minutes to about 5 seconds.

My hope is EF stored procedure mappings will be improved to achieve parody with EDMX and I can then just code-generate the Code-First mappings and remove the EDMX generation completely.