On what class can I find the extension 'Where' for the type DbSet<TEntity> of EF Core 5.0?

Question

I am writing a method that generates some EFCore Linq code using Linq expressions for a specific filtering API. It will write some statements like:

dbContext.Student
.Where(s => s.Address.ZipCode == 10005)
.Intersect(dbContext.Student
                    .Where(s => s.FirstName == "John")

For that I need get the MethodInfo of the Where and of the Intersect methods.

I tried using GetMethod on the type but it returns null (not working on extension methods):

MethodInfo method = typeof(Queryable).GetMethod("Where",
    BindingFlags.Public | BindingFlags.Static,
    null,
    CallingConventions.Any,
    new[] { typeof(IQueryable<Student>),
            typeof(Expression<Func<Student, bool>>)},
    null);

I also tried the following:

MethodInfo method = typeof(Queryable)
       .GetMethods(BindingFlags.Static | BindingFlags.Public)
       .Where(mi => mi.Name == "Where");
       // TO DO : taking the first of where Methods is bad.
       .First()
       .MakeGenericMethod(typeof(DbSet<Student>));

But I get a badArgument0 when used on DbSet.

Any clue of the class where I can find the right Where DbSet extension ?

Answer 1

You do not need MethodInfo here, you can create just call expression:

var queryable = dbContext.Student.AsQueryable();
var lambda = ...

var whereCall = Expression.Call(typeof(Queryable), 
     nameof(Queryable.Where), 
     new[] { typeof(Student) },
     queryable.Expression,
     lambda
  );

// and final
return queryable.Provider.CreateQuery<Student>(whereCall);