Convert Expression<Func<T, bool>> to another Predicate Expression Expression<Func<U, bool>> - linq

Question

I want to convert One predicate Expression(Expression<Func<Item, bool>>) to another Predicate Expression (Expression<Func<ItemEntity, bool>>) but after converting I am not able to query through LINQ.
I Already try this and this approach but nothing work properly
can anyone tells me how to do it properly, My approach for this problems.
using System;
using System.Linq;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Threading.Tasks;
using System.Reflection;
public class ItemEntity {
public int ItemId {set;get;}
public int ItemParentId {set;get;}
public int ItemName {set;get;}
}
public class Item {
public int Id{ set;get;}
public int ParentId{set;get;}
public int Name {set;get;}
}
public class Program
{
public static Item Convert(ItemEntity itemChild)
{
return new Item()
{
Id = itemChild.ItemId,
ParentId = itemChild.ItemParentId,
Name = itemChild.ItemName
};
}
public async Task<IList<ItemEntity>> SelectAsync(Expression<Func<ItemEntity, bool>> predicate)
{
// using Microsoft.EntityFrameworkCore;
// private readonly DbContext _context; // Injected globally by using Service.AddScoped<ItemContext>();
// return await _context.Set<ItemEntity>().AsNoTracking().Where(predicate).ToListAsync();
return await Task.Run(() => new List<ItemEntity>()); // actually return the result with matching predicate
}
public async Task<List<Item>> GetItems(Expression<Func<Item, bool>> expression)
{
MethodInfo convertMethod = ((Func<ItemEntity, Item>)Convert).Method;
var p = Expression.Parameter(typeof(ItemEntity));
var converted = Expression.Lambda<Func<ItemEntity, bool>>(
Expression.Invoke(expression, Expression.Convert(p, typeof(Item), convertMethod)), p);
IList<ItemEntity> res = await SelectAsync(converted);
var t = res.Select(x => Convert(x)).ToList();
return t;
}
public static void Main()
{
Program pr = new Program();
Func<Expression<Func<Item, bool>>, Task<List<Item>>> getItem = pr.GetItems;
var res = getItem.Invoke(x => x.Id.Equals(1));
Console.WriteLine("Hello World");
}
}
but I am getting error
The LINQ expression 'DbSet()\r\n .Where(i => ((Item)i).Id.Equals(__Id_0))' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync'. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.
I don't able to understand it properly, as per my understanding I am using ToList() for client evaluation, but and also provide method to convert ItemEntity to Item.
I any other way to create fresh Expression Tree based on ItemEntity and then query on DBSet?
Any Help is appreciated
version used:
dot-net 5.0
Microsoft.EntityFrameworkCore 5.0.6
EntityFramework 6.4.4
Database SQL Server

Answer 1

Try the following approach. Main idea to use filter exactly on the projected DTO before materialization.
using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Threading.Tasks;
public class ItemEntity
{
public int ItemId { set; get; }
public int ItemParentId { set; get; }
public int ItemName { set; get; }
}
public class Item
{
public int Id { set; get; }
public int ParentId { set; get; }
public int Name { set; get; }
}
public class Program
{
public static Expression<Func<ItemEntity, Item>> ToItem()
{
return itemChild => new Item
{
Id = itemChild.ItemId,
ParentId = itemChild.ItemParentId,
Name = itemChild.ItemName
};
}
public Task<IList<Item>> SelectAsync(Expression<Func<Item, bool>> predicate)
{
return _context.Set<ItemEntity>()
.AsNoTracking()
.Select(ToItem())
.Where(predicate)
.ToListAsync();
//return Task.Run(() => new List<ItemEntity>().AsQueryable().Select(ToItem()).Where(predicate).ToList());
}
public async Task<IList<Item>> GetItems(Expression<Func<Item, bool>> expression)
{
var res = await SelectAsync(expression);
return res;
}
public static void Main()
{
var pr = new Program();
var res = pr.GetItems(x => x.Id == 1);
Console.WriteLine("Hello World");
}
}