DbSet doesn't have a Find method in EF7

Question

I am trying to create a generic repository to access my database. In EF6 I was able to do that in order to get a specific entity:

protected IDbSet d         


        

Answer 1

In case you are using EF 7.0.0-rc1-final, below you find a small update for the code presented by @bricelam in the previous answer. By the way, thank you very much @bricelam - your code was extremely useful for me.

Here are my dependencies under "project.config":

"dependencies": {
    "EntityFramework.Commands": "7.0.0-rc1-final",
    "EntityFramework.MicrosoftSqlServer": "7.0.0-rc1-final",
    "Microsoft.Framework.Configuration.Json": "1.0.0-beta8",
    "Microsoft.Framework.ConfigurationModel": "1.0.0-beta4",
    "Microsoft.Framework.ConfigurationModel.Json": "1.0.0-beta4",
    "Microsoft.Framework.DependencyInjection": "1.0.0-beta8"
}

And below is the extension method for DbSet.Find(TEntity):

using Microsoft.Data.Entity;
using Microsoft.Data.Entity.Infrastructure;
using System;
using System.Linq;
using System.Linq.Expressions;

namespace Microsoft.Data.Entity.Extensions
{
    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 = entries.Where(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 = set.Where((Expression<Func<TEntity, bool>>)
                Expression.Lambda(
                    Expression.Equal(
                        Expression.Property(parameter, "Id"),
                        Expression.Constant(keyValues[0])),
                    parameter));

            // Look in the database
            return query.FirstOrDefault();
        }
    }
}

Answer 2

Find finally arrives into Entity Framework core.

Answer 3

I use linq; instead of Find method you can use:

var record = dbSet.SingleOrDefault(m => m.Id == id)

Answer 4

So...the above find methods worked great, but if you don't have a column named "Id" in your model, the whole thing is going to fail on the following line. I'm not sure why the OP would have put a hardcoded value into this spot

  Expression.Property(parameter, "Id"),

Here's a revision that will fix it for those that name our Id columns appropriately. :)

var keyCompare = key.Properties[0].Name;

        // TODO: Build the real LINQ Expression
        // set.Where(x => x.Id == keyValues[0]);
        var parameter = Expression.Parameter(typeof(TEntity), "x");
        var query = set.Where((Expression<Func<TEntity, bool>>)
            Expression.Lambda(
                Expression.Equal(
                    Expression.Property(parameter, keyCompare),
                    //Expression.Property(parameter, "Id"),
                    Expression.Constant(keyValues[0])),
                parameter));

        // Look in the database
        return query.FirstOrDefault();
    }

This STILL very well could fail if you have more than one Key setup on the entity object and the key you're looking up by isn't the first, but it should be quite a bit btter this way.

Answer 5

Not enough reputation to comment, but there is a bug in @Roger-Santana answer when using it in a console app/seperate assembly:

var i = 0;
foreach (var property in key.Properties)
{
    entries = entries.Where(e => e.Property(property.Name).CurrentValue == keyValues[i]);
    i++;
}
var entry = entries.FirstOrDefault();

The value of 'i' is captured in the foreach so that when entries.FirstOrDefault() is called, keyValues[i] has the value of (at least) keyValues[i++], which in my case crashed with an out of index error. A fix would be to copy the value of 'i' through the loop:

var i = 0;
foreach (var property in key.Properties)
{
   var idx =i;
    entries = entries.Where(e =>  e.Property(property.Name).CurrentValue == keyValues[idx]);
    i++;
}
var entry = entries.FirstOrDefault();