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Entity Framework in the Enterprise - Notes

Categories: EF Notes

by Julie Lerman

UI - Service Layer - Bus Layer - Repository/Unit of Work - Data Layer - Database

EF should stay in the data layer.
Split your context in smaller bounded contexts.

Bounded DbContext

  • Inspired on "Domain-Driven Design by Eric Evans" (domaindrivendesign.org)
  • All your navigation properties get pulled into the model.
  • Transition between context by id or by object.
  • Entity with property that is not persisted in the database: public decimal LineTotal { get; set; } ... In map class add Ignore(t => t.LineTotal)
  • Do not include navigation in the context: In OnModelCreating add modelBuilder.Ignore<T>();
  • Make sure non related is included: In OnModelCreating add modelBuilder.Entity<T>();
  • Migrations and creations: Add one model that includes all of your tables and use this one.
  • Put each context in it's own project.
  • Put the mappings also in their separated project. eg. BaseDataLayer - CompanyDatabaseInitializers - CustomerServiceBoundedContext - DataLayerMappings - DomainClasses - ReturnsBoundedContext - SalesBoundedContext
  • Use EF powertools to visualize your context and see what will be pulled in.
  • And then cherry pick what you need (eg. probably do not need the relationships)

Repositories and Unit of Work

  • Encapsulate Redundant Data Access Code
  • GetCustomerById(cid), GetAllCustomers, GetCurrentCustomers, GetLocalCustomers, GetFilteredCustomers
  • RemoveCustomer, AddCustomer

Install-Package entityframework
Install-Package t4scaffolding

scaffold repository DomainClasses.Customer -DbContextType:SalesContext

Always use ctx.Customers.Find(id) cause it will not roundtrip when not needed.

DbSet.Add(root) - All elements State=Added - Insert for each element, even if pre-existing in db
DbSet.Attach(root) - All elements State=Unchanged - Any new records with missing FKs will throw
Context.Entry(root).State=EntityState - Context attaches full graph, all entities State=Unchanged, Root (only) set to specific state - Any new with missing FKs will throw

Disconnected Graph
Attaching to Context: all new -> DbSet.Add(customer)
Root new, existing unchanged: Entry(customer).State=Added
Editing: Entry(customer).State=Modified then Entry(*each item*).State=Modified
Root edited and added: DbSet.Add(customer) then Entry(*each non added*).State=*correct state*

Make objects track their own state:
IObjectWithState
enum State { Added, Unchanged, Modified, Deleted }

public abstract class Person:IObjectWithState
[NotMapped]
public State State { get; set;}

Repository depends on the value of client-side State
Developer using repository MUST set client-side State!

StateHelpers - EntityState ConvertState(State state)
ContextHelpers - ApplyStateChanges(this DbContext context)

Difference between long running and short running context (or implement two repos)

Let repositories share the same context (Unit of work)
Move save method to unit of work
CustomerRepository contains Unit of work that contains a context

ReferencesContext
Especially when reading data: _context.Customers.AsNoTracking();

A DbSet represents the collection of all entities in the context, or that can be queried from the database, of a given type.
DbSet object are created from a DbContext using the DbContext.Set method
A DbContext instance represents a combination of the unit of work and repository patterns such that it can be used to query a database and group together changes that will then be written back to the store as a unit. DbContext is conceptually similar to ObjectContext.

  • Why build a repository on top op EF? EF is a repository!
  • Should you return an IQueryable from a repository
  • How much abstraction and refactoring? There will always be more.

Automated Testing Overview

  • Unit Testing
  • Integration Testing
  • Interaction Testing
  • System Testing
  • User Interface Testing

1. Complete model with Seed method
2. Initialize Database for each integration test
3. Use a testing database that can get destroyed frequently

Test your data annotations: test for DbEntityValidationException

Fake Context & Fake Data
IDbSet<TEntity> : DbQuery<TEntity>, IDbSet<TEntity>, IQueryable<TEntity>, IEnumerable<TEntity>, IQueryable, IEnumerable where TEntity : class

(you can also use IObjectSet)
public abstract class MyFakeDbSet<T> : IDbSet<T> where T : class, new()
{
}

Create implementation to override the find method

IUoW needs IContext

SalesPromotionAccessor (to hide the context and wrap it with your unit of work)