Code First without dropping the database

I have been using the Entity Framework code first options for a prototype application architecture. I have the database initializer setup called from my unit tests to validate the integration work I’m doing. This is working fine for me now. However, in most enterprise applications the developer would not be responsible for generating the database – much less dropping and re-creating the database and all of the table objects.

Therefore, I’m going to change the approach a little bit. I still want to do code first in terms of setting up my entity classes. However, I want a little more flexibility in working in a team environment where there is a dedicated DBA who is responsible for managing the database objects. The sample database that I’m using for the code first EF contains a table called EdmMetadata. I’m going to remove this table from the database – so that it is not used as part of the initialization. This means my database will not be dropped when the initializer is called.

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I will also remove the call from my unit test Setup() method.

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The unit test runs and passes – this is good news. Now I do not have the dependency on the database initialization process.

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Now, I’d like to add a new entity item that maps to a new table in my database. I can define the entity first and create the table object later. You might be wondering why I’m not using the EF tooling. My data access doesn’t contain an .edmx file – I am using a generic Entity Framework Repository<T> pattern with the future possibilities of code generating the plumbing classes later using the entity class as a meta file for the code generator.

New Entity and Database Table

I am now creating a new entity with a matching table in the database.

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The Coder entity uses a base class for default entity behavior and implements the IEntity interface – which means that there must be an Id property for the entity.

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Generic Entity Framework Repository

I have some infrastructure repository classes that provide the default implementation of the EF calls for a specified entity. To do the wire-up, I create an interface called ICoderRepository that implements the IRepository<T> class. This will allow me to add an extended behavior not already contained or implemented in the generic repository classes. I also create a CoderRepository class which is the concrete implementation for the Coder entity’s repository. It implements the GenericRepository<T>

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I do have a DbContext class that the generic repository is using for data access. I just need to let it know about the new entity that I have created. Therefore, I create a partial class for my context CodeDb and add the DbSet<Coder> public property. Note: the name of the DbSet<Coder> property should match the name of the database table – if your database table has a different name, I am sure you can just attribute the table name on the entity itself.

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Now my CodeDb context will know about my new entity and will be able to perform data access.

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So, if you are keeping track, we have added (2) classes and (1) interface to implement the EF Repository for the Coder entity. Using this approach will allow me to later generate these plumbing classes and wire-up entity repositories with ease. But without the code generator, it still isn’t that much wire-up. I like the convenience of the Generic Repository and the partial classes to add to the core infrastructure of the DbContext and Repositories. Now that the repository is configured, I can create another partial class that will enable access to the repository from business logic classes. There is no .edmx file to manage or now specialized EF connection strings – we can just use a standard connection string name (note: I send in the name of the connection string only) in the configuration file and the DbContext constructor does the rest.

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The Wire-Up using Dependency Injection

Now for really cool part. It is all wired-up using dependency injection. The DI container will scan the assembly for specific repository implementations and initialize the concrete repositories during runtime.

My business object BusinessProvider contains the injected repository CoderRepository – with the ability to use the GenericRepository methods to add the entity to the corresponding database table.

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I run my unit test and everything is good – the data made it into the database.

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Conclusion

So, after creating the entity, I added some partial classes to onboard the entity into the generic repository and the DbContext – I consider this plumbing/infrastructure code. Then I added another partial class to add the CoderRepository reference to the BusinessProvider business class. Then with a single method call, no additional coding required, I was able to perform the data transaction to the specified database.

The implementation details only took a few minutes to setup. There is definitely a recipe here to make sure that all of the infrastructure classes are setup. These are there primarily for extensibility in the case you need to add some specialized behavior that is not already implemented in the generic repository. I like the approach of having a single repository for each entity in your solution. Using the partial classes enables that. What I didn’t include in this post is how the Generic Repository<T> works and how dependency injection is used to perform the wire-up.

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