DBSet.Find() API missing in Entity Framework Core Final RC1 Version

Rahul Sahay
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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.

using System;
using System.Linq;
using System.Linq.Expressions;
using Microsoft.Data.Entity;
using Microsoft.Data.Entity.Infrastructure;
namespace MovieReviewSPA.Data.Helpers
{
public static class Extensions
{
public static TEntity Find<TEntity>(this DbSet<TEntity> set, params object[] keyValues) where TEntity : class
{
var context = ((IInfrastructure<IServiceProvider>)set).GetService<DbContext>();
var entityType = context.Model.FindEntityType(typeof(TEntity));
var key = entityType.FindPrimaryKey();
var entries = context.ChangeTracker.Entries<TEntity>();
var i = 0;
foreach (var property in key.Properties)
{
entries = Enumerable.Where(entries, e => e.Property(property.Name).CurrentValue == keyValues[i]);
i++;
}
var entry = entries.FirstOrDefault();
if (entry != null)
{
// Return the local object if it exists.
return entry.Entity;
}
// TODO: Build the real LINQ Expression
// set.Where(x => x.Id == keyValues[0]);
var parameter = Expression.Parameter(typeof(TEntity), "x");
var query = Queryable.Where(set, (Expression<Func<TEntity, bool>>)
Expression.Lambda(
Expression.Equal(
Expression.Property(parameter, "Id"),
Expression.Constant(keyValues[0])),
parameter));
// Look in the database
return query.FirstOrDefault();
}
}
}

And, here is the completed Repository Pattern for my project.

using System;
using System.Linq;
using Microsoft.Data.Entity;
using Microsoft.Data.Entity.ChangeTracking;
using MovieReviewSPA.Data.Contracts;
using MovieReviewSPA.Data.Helpers;
using DbContext = Microsoft.Data.Entity.DbContext;
using EntityState = Microsoft.Data.Entity.EntityState;
namespace MovieReviewSPA.Data
{
public class EFRepository<T> : IRepository<T> where T : class
{
public EFRepository(DbContext dbContext)
{
if (dbContext == null)
throw new ArgumentNullException("dbContext");
DbContext = dbContext;
DbSet = DbContext.Set<T>();
}
protected DbContext DbContext { get; set; }
protected DbSet<T> DbSet { get; set; }
public virtual IQueryable<T> GetAll()
{
return DbSet;
}
public virtual T GetById(int id)
{
//EF Core Will be updated shortly with Find Extension by Default
//Here, I have written Extension method for the same
//Source:- http://stackoverflow.com/questions/29030472/dbset-doesnt-have-a-find-method-in-ef7/29082410#29082410
return DbSet.Find(id);
}
public virtual void Add(T entity)
{
EntityEntry<T> dbEntityEntry = DbContext.Entry(entity);
if (dbEntityEntry.State != (EntityState) EntityState.Detached)
{
dbEntityEntry.State = EntityState.Added;
}
else
{
DbSet.Add(entity);
}
}
public virtual void Update(T entity)
{
EntityEntry<T> dbEntityEntry = DbContext.Entry(entity);
if (dbEntityEntry.State != (EntityState) EntityState.Detached)
{
DbSet.Attach(entity);
}
dbEntityEntry.State = EntityState.Modified;
}
public void Delete(T entity)
{
EntityEntry<T> dbEntityEntry = DbContext.Entry(entity);
if (dbEntityEntry.State != (EntityState) EntityState.Deleted)
{
dbEntityEntry.State = EntityState.Deleted;
}
else
{
DbSet.Attach(entity);
DbSet.Remove(entity);
}
}
public void Delete(int id)
{
var entity = GetById(id);
if (entity == null) return;
Delete(entity);
}
}
}

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.