How to use ToQuery outside the DbContext?

[Neme12]

In a DbContext's OnModelCreating method, I can use ToQuery to map an entity type to a LINQ query as opposed to a table:

public sealed class Record
{
    public int Id { get; set; }
    public string Value { get; set; }
}

public sealed class RecordData
{
    public string Value { get; set; }
}

public sealed class ApplicationDbContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<RecordData>().HasNoKey().ToQuery(() => Records.Select(r => new RecordData { Value = r.Value }));
    }

    public DbSet<Record> Records { get; set; }
    public DbSet<RecordData> RecordData { get; set; }
}

but in our project, we like to use IEntityTypeConfiguration classes to configure each entity type and then call ApplyConfiguration from inside the DbContext as opposed to having any configuration directly there.

My question is, how to define the query passed to ToQuery in such a configuration class outside of the DbContext?

public sealed class RecordDataConfiguration : IEntityTypeConfiguration<RecordData>
{
    public void Configure(EntityTypeBuilder<RecordData> builder)
    {
        builder.HasNoKey().ToQuery(/* what goes here? */);
    }
}

I would expect the lambda in ToQuery to take a DbContext as the parameter so that I could do something like this:

builder.HasNoKey().ToQuery(context => context.Set<Record>().Select(r => new RecordData { Value = r.Value }));

but I don't see that being the case and can't think of any way to get the DbContext or DbSet for a specific entity type here. Am I missing something? What's the correct way to do this?

[ajcvickers]

@Neme12 I just tested this and it works for me.

public sealed class RecordDataConfiguration : IEntityTypeConfiguration<RecordData>
{
    private readonly DbContext _context;

    public RecordDataConfiguration(DbContext context)
    {
        _context = context;
    }

    public void Configure(EntityTypeBuilder<RecordData> builder)
    {
        builder.HasNoKey().ToQuery(() => _context.Set<Record>().Select(r => new RecordData { Value = r.Value }));
    }
}

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        new RecordDataConfiguration(this).Configure(modelBuilder.Entity<RecordData>());
    }

It's probably also worth noting that ToQuery is not an area we are currently happy with and we plan to make changes in 5.0. See #18903 and #17270

[smitpatel]

If it works for you then it works for everyone.

[stevendarby]

@ajcvickers due to model caching is there not a chance that will capture the initial context only?

[ajcvickers]

@Snappyfoo I don't think so, no.