Adding a where to a generic expression in a custom Entity Framework Core .Include

Question

We have a custom static class containing a custom .Include method to be used when using Entity Framework Core to call a repository. We would like the include to take whatever selector has been provided, for example i.Documents as shown here:

private readonly IRepository<Item> _itemRepository;

var item = await _itemRepository.GetAll()
                                .IncludeCheckingSecurity(i => i.Documents)
                                .SingleAsync();

And if the repository is of a certain type (IObjectWithSecurity) and the selector is of a certain type (IEnumerable of IObjectWithSecurity) to add an additional .Where() for the selector filtering on a property that exists on IObjectWithSecurity:

public static IIncludableQueryable<TRepositoryType, TThisInclude> IncludeCheckingSecurity<TRepositoryType, TThisInclude>(
this IQueryable<TRepositoryType> source,
Expression<Func<TRepositoryType, TThisInclude>> propertySelector)
where TRepositoryType : class
{
   var previousType = typeof(TRepositoryType);
   var thisInclude = typeof(TThisInclude);

   if (typeof(IObjectWithSecurity).IsAssignableFrom(previousType) && typeof(IEnumerable<IObjectWithSecurity>).IsAssignableFrom(thisInclude))
   {
       // Want to add a where to 'propertySelector' which filters it on a property within IObjectWithSecurity (which we have proved it is above)
       return source.Include(propertySelector);
   }
}

EDIT

For example, this call to the repository:

private readonly IRepository<Item> _itemRepository;

var item = await _itemRepository.GetAll()
                            .IncludeCheckingSecurity(i => i.Documents)
                            .SingleAsync();

Should actually result in this:

private readonly IRepository<Item> _itemRepository;

var item = await _itemRepository.GetAll()
                            .IncludeCheckingSecurity(i => i.Documents.Where(a => a.AllowAccess))
                            .SingleAsync();

Where i.Documents is an Enumerable of a type that inherits from IObjectWithSecurity. And AllowAccess is a property on IObjectWithSecurity:

public interface IObjectWithSecurity 
{
    public bool AllowAccess { get; set; }
}

We have experimented with creating additional expressions and using lambda to join them:

Expression<Func<TThisInclude, bool>> whereToAppend = e => ((IObjectWithSecurity)e).AllowAccess;
var newIncludeWithWhere = Expression.Lambda<Func<TRepositoryType, TThisInclude>>(Expression.AndAlso(propertySelector, whereToAppend), propertySelector.Parameters);
return source.Include(newIncludeWithWhere);

But without success as it seems this is more designed for joining 2 where expressions instead of a member access expression and a where expression on its collection.

Too abstract question. Everything is possible, but which expression you expect after transformation? I cannot handle it from original question. — Svyatoslav Danyliv
– Svyatoslav Danyliv, Commented Nov 7, 2024 at 17:24
There's a repository class that has this all nicely implemented: DbSet. It always strikes me as a bit weird that so many people bury EF DbSets in a repository and then jump through hoops and loops to dig all kinds of tunnels to it. All under the guise of abstraction, which is immediately broken by EF-specific methods like this. — Gert Arnold
– Gert Arnold, Commented Nov 7, 2024 at 20:03
I believe that this might point you in the right direction: stackoverflow.com/questions/27669993/… — akseli
– akseli, Commented Nov 8, 2024 at 1:05
@SvyatoslavDanyliv - the return of the whole static method will be IIncludableQueryable<TRepositoryType, TThisInclude>. propertySelector should end up as Expression<Func<TRepositoryType, TThisInclude>>. We want to take a memberaccess expression that is inputted (propertySelector) and add a where clause to it. However it will be a generic type and will need casting to IObjectWithSecurity if it is indeed assignable. There is then a boolean on IObjectWithSecurity which we want to verify is true. Hope this helps — sjones
– sjones, Commented Nov 8, 2024 at 10:22

Svyatoslav Danyliv · Accepted Answer · 2024-11-08 11:28:08Z

This extension enables adding an additional security filter to the Include expression:

public static class SecurityExtensions
{
    public static IIncludableQueryable<TEntity, IEnumerable<TProperty>> IncludeCheckingSecurity<TEntity, TProperty>(this IQueryable<TEntity> query, Expression<Func<TEntity, IEnumerable<TProperty>>> property) 
        where TProperty : IObjectWithSecurity 
        where TEntity : class
    {
        // Define a template filter expression to apply access checking
        Expression<Func<IEnumerable<TProperty>, IEnumerable<TProperty>>> filterTemplate = p => p.Where(x => x.AllowAccess);

        // Replace parameters in the template with those from the property expression
        var newIncludeBody = ReplacingExpressionVisitor.Replace(filterTemplate.Parameters[0], property.Body, filterTemplate.Body);

        // Create a new lambda expression using the modified include body
        var newIncludeLambda = Expression.Lambda<Func<TEntity, IEnumerable<TProperty>>>(newIncludeBody, property.Parameters);

        // Apply the modified include expression with security filtering
        return query.Include(newIncludeLambda);
    }
}

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