Entity Framework Code First

This is another dump of my notes from a talk at Prairie Dev Con. This is David Paquette’s Entity Framework Code First talk which is, oddly, subtitled Magic Unicorn. Very odd.

David is also a beautiful unicorn

- EF shipped with VS 2008 and was junk

• ORM is tough, please don’t write your own
• There are 3 flavours of EF model first, database first and code first.
• Model first using a visual designer to build up a model of the data. Kind of like LINQ
• Database first will generate you a model from an existing database
• Code first you create POCOs first and use conventions to figure out things like the key and foreign key references
• Conventions - virtual IList or IColleciton creates a foreign key to the collection of Somethings.
• virtual Something creates a one to one mapping from the current object to a Something
• any property called Id becomes a primary key
• EF will create a database using the name of the DbContext if there is no configured database
• Good idea to initialize collections in the constructor. Using a HashSet is more efficient than using a List because hash set optimizes for having no duplicates.
• A DbContext provides a mapping from the objects to the database. Each entity is just set up as an IDbSet in the DbContext.
• The LINQ queries return IQueryables which are a built up collection of lambads which are applied in a delayed or lazy fashion
• It is important to convert the IQuerable to an array or list before passing the data to the view as the DbContext may be out of scope before the view is rendered
• You should dispose your DbContext as that returns the connection to the pool. This is best done using a handy, dandy injection framework. In this case Ninject.
• To return a single object you might call _dbContext.Somethings.Find(id) you can also use Single or First which have slightly different failure criteria.
• To add an entity use an Add on the context and then call SaveChanges to synchronize the DbContext with the database
• Tidbit: There are no performance implications to using varchar(max) except that varchar(max) cannot be indexed so it can’t be easily searched.
• When editing an entity you need to mark the state as modified _dbContext.Somethings(entity).State = EntityState.Modified.
• You can specify a database initializer where you can have it delete and recreate a database or add default data
• You can profile your applications using MiniProfiler.MVC which is a lightweight profiler from Stackoverflow. To hook in EF include MiniProfiler.EF
• You can to eager loading by specifying .Include(“Something.Comments”) this would load the comments collection for Something
• Projections can be used to trim down what is returned form the database
• Paging is implemented using Skip and Take

Thoughts:

EF is a lot of magic but it seems like pretty well thought out and easily overridable magic.