EF.Property is not working in .Include. Is it a bug or intended?

[paxbun]

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using System.Linq.Expressions;
using System.Reflection;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;
using Microsoft.EntityFrameworkCore.Metadata.Builders;
using Microsoft.Extensions.Configuration;

var configuration = new ConfigurationBuilder()
    .AddUserSecrets(Assembly.GetExecutingAssembly())
    .Build();
var versionString = configuration["MySQL:Version"];
var connectionString = configuration["MySQL:ConnectionString"];

Console.WriteLine("MySQL:Version = {0}", versionString);

var version = new MySqlServerVersion(new Version(versionString));
var options = new DbContextOptionsBuilder<MySqlApplicationDbContext>();

options.UseMySql(connectionString, version);

using MySqlApplicationDbContext dbContext = new(options.Options);

dbContext.Entities.RemoveRange(dbContext.Entities);
dbContext.SaveChanges();

{
    Entity entity = new();
    entity.AddVersion("Foo");
    entity.AddVersion("Bar");
    entity.AddVersion("Baz");
    dbContext.Entities.Add(entity);
}
{
    Entity entity = new();
    entity.AddVersion("Hello");
    entity.AddVersion("Bye");
    dbContext.Entities.Add(entity);
}

dbContext.SaveChanges();

{
    // System.InvalidOperationException: The expression 'Property(e, "_entityVersions")' is invalid inside
    // an 'Include' operation, since it does not represent a property access: 't => t.MyProperty'. To target
    // navigations declared on derived types, use casting ('t => ((Derived)t).MyProperty') or the 'as' operator
    // ('t => (t as Derived).MyProperty'). Collection navigation access can be filtered by composing Where,
    // OrderBy(Descending), ThenBy(Descending), Skip or Take operations. For more information on including
    // related data, see http://go.microsoft.com/fwlink/?LinkID=746393.
    //
    //
    var entities = (
        from e in dbContext.Entities
            .Include(e => EF.Property<EntityVersion>(e, "_entityVersions"))
        select e
    ).ToArray();

    // works well 1
    // var entities = (
    //     from e in dbContext.Entities
    //         .Include("_entityVersions")
    //     select e
    // ).ToArray();

    // works well 2
    // var param = Expression.Parameter(typeof(Entity));
    // var field = typeof(Entity).GetField("_entityVersions", BindingFlags.Instance | BindingFlags.NonPublic)!;
    // var fieldAccess = Expression.Field(param, field);
    // var expression = Expression.Lambda<Func<Entity, IList<EntityVersion>>>(fieldAccess, param);
    // var entities = (
    //     from e in dbContext.Entities
    //         .Include(expression)
    //     select e
    // ).ToArray();
    
    foreach (var entity in entities)
    {
        Console.WriteLine("Entity {0}:", entity.Id);
        foreach (var entityVersion in entity.EntityVersions)
        {
            Console.WriteLine(" - Value: {0}", entityVersion.Value);
        }
    }
}

public class MySqlApplicationDbContext : DbContext
{
    public DbSet<Entity> Entities { get; set; } = null!;
    public DbSet<EntityVersion> EntityVersions { get; set; } = null!;

    public MySqlApplicationDbContext(DbContextOptions options)
        : base(options)
    {
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyConfigurationsFromAssembly(Assembly.GetExecutingAssembly());
    }
}


public class MySqlDbContextFactory : IDesignTimeDbContextFactory<MySqlApplicationDbContext>
{
    public MySqlApplicationDbContext CreateDbContext(string[] args)
    {
        var configuration = new ConfigurationBuilder()
            .AddUserSecrets(Assembly.GetExecutingAssembly())
            .Build();
        var versionString = configuration["MySQL:Version"];
        var connectionString = configuration["MySQL:ConnectionString"];

        Console.WriteLine("MySQL:Version = {0}", versionString);

        var version = new MySqlServerVersion(new Version(versionString));
        var options = new DbContextOptionsBuilder<MySqlApplicationDbContext>();

        options.UseMySql(connectionString, version);

        return new(options.Options);
    }
}

public class EntityVersion
{
    public Guid Id { get; }
    public Guid EntityId { get; }
    public int Version { get; set; }
    public string Value { get; set; } = null!;

    public EntityVersion()
    {
    }

    public EntityVersion(Entity entity, string value)
    {
        Id = Guid.NewGuid();
        EntityId = entity.Id;
        Version = entity.AdvanceVersion();
        Value = value;
    }
}

public class EntityVersionConfiguration : IEntityTypeConfiguration<EntityVersion>
{
    public void Configure(EntityTypeBuilder<EntityVersion> builder)
    {
        builder.HasKey(m => m.Id);
        builder.Property(m => m.Id)
            .IsRequired();
        builder.Property(m => m.Version)
            .IsRequired();
        builder.HasIndex(m => m.Version);
        builder.Property(m => m.Value)
            .IsRequired();
        builder.HasOne<Entity>()
            .WithMany("_entityVersions")
            .HasForeignKey(m => m.EntityId)
            .OnDelete(DeleteBehavior.Cascade);
    }
}

public class Entity
{
    public Guid Id { get; }
    public int PublicVersion { get; private set; }
    public IEnumerable<EntityVersion> EntityVersions => _entityVersions;
    private readonly IList<EntityVersion> _entityVersions;

    public Entity()
    {
        Id = Guid.NewGuid();
        PublicVersion = 0;
        _entityVersions = new List<EntityVersion>();
    }

    public int AdvanceVersion()
    {
        return ++PublicVersion;
    }

    public void AddVersion(string value)
    {
        _entityVersions.Add(new EntityVersion(this, value));
    }
}

public class EntityConfiguration : IEntityTypeConfiguration<Entity>
{
    public void Configure(EntityTypeBuilder<Entity> builder)
    {
        builder.HasKey(m => m.Id);
        builder.Property(m => m.PublicVersion)
            .IsRequired();
        builder.Ignore(m => m.EntityVersions);
    }
}

Include stack traces

Include the full exception message and stack trace for any exception you encounter.

Use triple-tick fences for stack traces. For example:

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at SixFour.Sub() in C:\Stuff\AllTogetherNow\SixFour\SixFour.cs:line 49
   at SixFour.Main() in C:\Stuff\AllTogetherNow\SixFour\SixFour.cs:line 54

Include verbose output

Please include verbose output when asking questions about the dotnet ef or Package Manager Console tools.

System.InvalidOperationException: The expression 'Property(e, "_entityVersions")' is invalid inside an 'Include' operation, since it does not represent a property access: 't => t.MyProperty'. To target navigations declared on derived types, use casting ('t => ((Derived)t).MyProperty') or the 'as' operator ('t => (t as Derived).MyProperty'). Collection navigation access can be filtered by composing Where, OrderBy(Descending), ThenBy(Descending), Skip or Take operations. For more information on including related data, see http://go.microsoft.com/fwlink/?LinkID=746393.
at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.<ProcessInclude>g__ExtractIncludeFilter|32_0(Expression currentExpression, Expression includeExpression)
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.ProcessInclude(NavigationExpansionExpression source, Expression expression, Boolean thenInclude, Boolean setLoaded)
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.Expand(Expression query)
   at Microsoft.EntityFrameworkCore.Query.QueryTranslationPreprocessor.Process(Expression query)
   at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass9_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1.GetEnumerator()
   at System.Collections.Generic.LargeArrayBuilder`1.AddRange(IEnumerable`1 items)
   at System.Collections.Generic.EnumerableHelpers.ToArray[T](IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Program.<Main>$(String[] args) in .../Program.cs:line 51

Include provider and version information

EF Core version: 6.0.1
Database provider: Pomelo.EntityFrameworkCore.MySql 6.0.1
Target framework: .NET 6.0
Operating system: macOS
IDE: Rider 2021.3.3

[paxbun]

Note that the version which uses LINQ APIs to get private field works, i.e.,

var param = Expression.Parameter(typeof(Entity));
var field = typeof(Entity).GetField("_entityVersions", BindingFlags.Instance | BindingFlags.NonPublic)!;
var fieldAccess = Expression.Field(param, field);
var expression = Expression.Lambda<Func<Entity, IList<EntityVersion>>>(fieldAccess, param);
var entities = (
    from e in dbContext.Entities
        .Include(expression)
    select e
).ToArray();

[ajcvickers]

@paxbun Because a) it's not implemented, and b) it would probably be more appropriate to introduce a Navigation method for this, since it is about referencing a navigation rather than a normal property. See #27493.

[paxbun]

@ajcvickers Then, if I want to use .ThenInclude, is using the LINQ APIs the only way to achieve this at the moment?

[ajcvickers]

@paxbun Typically if you are building these includes dynamically, then it is easier to just use strings for the navigations to load. For example, .Include("_entityVersions").