Recently, I was writing the infrastructure part of My Movie Review SPA app using ASP.NET Core version. Then, I landed in a really weird situation where in DBSet.Find() a piece is missing. This is a really crucial extension method for finding the record based on the primary key. In order to find the solution, I thought it would be nice to talk to EF Guru Julie Lerman directly. Here is what I asked her and what she replied on the same.

Here, at this point I got the confirmation, this feature is yet to be included by EF Team. Hence, I decided to use the interim solution provided by the EF Team themselves. Below is the extension method which I have written to serve the same result.
  1. using System;
  2. using System.Linq;
  3. using System.Linq.Expressions;
  4. using Microsoft.Data.Entity;
  5. using Microsoft.Data.Entity.Infrastructure;
  7. namespace MovieReviewSPA.Data.Helpers
  8. {
  9. public static class Extensions
  10. {
  11. public static TEntity Find<TEntity>(this DbSet<TEntity> set, params object[] keyValues) where TEntity : class
  12. {
  13. var context = ((IInfrastructure<IServiceProvider>)set).GetService<DbContext>();
  15. var entityType = context.Model.FindEntityType(typeof(TEntity));
  16. var key = entityType.FindPrimaryKey();
  18. var entries = context.ChangeTracker.Entries<TEntity>();
  20. var i = 0;
  21. foreach (var property in key.Properties)
  22. {
  23. entries = Enumerable.Where(entries, e => e.Property(property.Name).CurrentValue == keyValues[i]);
  24. i++;
  25. }
  27. var entry = entries.FirstOrDefault();
  28. if (entry != null)
  29. {
  30. // Return the local object if it exists.
  31. return entry.Entity;
  32. }
  34. // TODO: Build the real LINQ Expression
  35. // set.Where(x => x.Id == keyValues[0]);
  36. var parameter = Expression.Parameter(typeof(TEntity), "x");
  37. var query = Queryable.Where(set, (Expression<Func<TEntity, bool>>)
  38. Expression.Lambda(
  39. Expression.Equal(
  40. Expression.Property(parameter, "Id"),
  41. Expression.Constant(keyValues[0])),
  42. parameter));
  44. // Look in the database
  45. return query.FirstOrDefault();
  46. }
  47. }
  48. }
And, here is the completed Repository Pattern for my project.
  1. using System;
  2. using System.Linq;
  3. using Microsoft.Data.Entity;
  4. using Microsoft.Data.Entity.ChangeTracking;
  5. using MovieReviewSPA.Data.Contracts;
  6. using MovieReviewSPA.Data.Helpers;
  7. using DbContext = Microsoft.Data.Entity.DbContext;
  8. using EntityState = Microsoft.Data.Entity.EntityState;
  10. namespace MovieReviewSPA.Data
  11. {
  12. public class EFRepository<T> : IRepository<T> where T : class
  13. {
  14. public EFRepository(DbContext dbContext)
  15. {
  16. if (dbContext == null)
  17. throw new ArgumentNullException("dbContext");
  18. DbContext = dbContext;
  19. DbSet = DbContext.Set<T>();
  20. }
  22. protected DbContext DbContext { get; set; }
  23. protected DbSet<T> DbSet { get; set; }
  24. public virtual IQueryable<T> GetAll()
  25. {
  26. return DbSet;
  27. }
  29. public virtual T GetById(int id)
  30. {
  31. //EF Core Will be updated shortly with Find Extension by Default
  32. //Here, I have written Extension method for the same
  33. //Source:- http://stackoverflow.com/questions/29030472/dbset-doesnt-have-a-find-method-in-ef7/29082410#29082410
  34. return DbSet.Find(id);
  35. }
  37. public virtual void Add(T entity)
  38. {
  39. EntityEntry<T> dbEntityEntry = DbContext.Entry(entity);
  40. if (dbEntityEntry.State != (EntityState) EntityState.Detached)
  41. {
  42. dbEntityEntry.State = EntityState.Added;
  43. }
  44. else
  45. {
  46. DbSet.Add(entity);
  47. }
  48. }
  50. public virtual void Update(T entity)
  51. {
  52. EntityEntry<T> dbEntityEntry = DbContext.Entry(entity);
  53. if (dbEntityEntry.State != (EntityState) EntityState.Detached)
  54. {
  55. DbSet.Attach(entity);
  56. }
  57. dbEntityEntry.State = EntityState.Modified;
  58. }
  60. public void Delete(T entity)
  61. {
  62. EntityEntry<T> dbEntityEntry = DbContext.Entry(entity);
  63. if (dbEntityEntry.State != (EntityState) EntityState.Deleted)
  64. {
  65. dbEntityEntry.State = EntityState.Deleted;
  66. }
  67. else
  68. {
  69. DbSet.Attach(entity);
  70. DbSet.Remove(entity);
  71. }
  72. }
  74. public void Delete(int id)
  75. {
  76. var entity = GetById(id);
  77. if (entity == null) return;
  79. Delete(entity);
  80. }
  81. }
  83. }
Now, below is the glimpse of the solution structure so far for my Movie Review SPA coming up using ASP.NET Core, WEB-API, Angular JS, Entity Framework and tons of new things.



I hope you have liked this discussion. Thanks for joining me.