using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;

await using var ctx = new BlogContext();
await ctx.Database.EnsureDeletedAsync();
await ctx.Database.EnsureCreatedAsync();

var queryA = ctx.EntityA
    .Select(x => new CombinedDto
    {
        Id = x.Id,
        EntityCDto = x.EntityCs
            .OrderBy(x => x.Id)
            .Select(x => new EntityCDto { Value1 = x.Value1, Value2 = x.Value2 })
            .FirstOrDefault()
    });

var queryB = ctx.EntityB
    .Select(x => new CombinedDto
    {
        Id = x.Id,
        EntityCDto = x.EntityCs
            .OrderBy(x => x.Id)
            .Select(x => new EntityCDto { Value1 = x.Value1, Value2 = x.Value2 })
            .FirstOrDefault()
    });

// Query A works on its own
_ = await queryA.ToListAsync();

// Query B works on its own
_ = await queryB.ToListAsync();

// Query A + B fails
var concatQuery = queryA.Concat(queryB);
_ = await concatQuery.ToListAsync();

public class BlogContext : DbContext
{
    public DbSet<EntityA> EntityA { get; set; }
    public DbSet<EntityB> EntityB { get; set; }
    public DbSet<EntityC> EntityC { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=SetFailure;Trusted_Connection=True;Encrypt=False")
            .LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder
            .Entity<EntityA>()
            .HasMany(x => x.EntityCs);
        modelBuilder
            .Entity<EntityB>()
            .HasMany(x => x.EntityCs);
    }
}

public class EntityBase
{
    public Guid Id { get; set; }
}

public class EntityA : EntityBase
{
    public ICollection<EntityC> EntityCs { get; set; } = [];
}

public class EntityB : EntityBase
{
    public ICollection<EntityC> EntityCs { get; set; } = [];
}

public class EntityC : EntityBase
{
    public required string Value1 { get; set; }
    public required string Value2 { get; set; }
}

public class CombinedDto
{
    public Guid Id { get; set; }
    public EntityCDto? EntityCDto { get; set; }
}

public class EntityCDto
{
    public required string Value1 { get; set; }
    public required string Value2 { get; set; }
}

using AutoMapper;
using AutoMapper.QueryableExtensions;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;

var mapper = new MapperConfiguration(
    a =>
    {
        a.CreateMap<EntityA, CombinedDto>()
            .ForMember(x => x.EntityCDto, o => o.MapFrom(x => x.EntityCs.OrderBy(x => x.Id).FirstOrDefault()));

        a.CreateMap<EntityB, CombinedDto>()
            .ForMember(x => x.EntityCDto, o => o.MapFrom(x => x.EntityCs.OrderBy(x => x.Id).FirstOrDefault()));

        a.CreateMap<EntityC, EntityCDto>();
    }, new LoggerFactory())
    .CreateMapper();

await using var ctx = new BlogContext();
await ctx.Database.EnsureDeletedAsync();
await ctx.Database.EnsureCreatedAsync();

var queryA = ctx.EntityA.ProjectTo<CombinedDto>(mapper.ConfigurationProvider);

var queryB = ctx.EntityB.ProjectTo<CombinedDto>(mapper.ConfigurationProvider);

// Query A works on its own
_ = await queryA.ToListAsync();

// Query B works on its own
_ = await queryB.ToListAsync();

// Query A + B fails
var concatQuery = queryA.Concat(queryB);
_ = await concatQuery.ToListAsync();

// snip - same context and models as above