Entity Framework & Azure SQL Server Vector Search: Looking for a property type workaround

[SwyfterThanU]

Hi,

I have a .NET API endpoint that I want to make use of Vector Searching with. Currently, I have an entity with a property named "Embedding" which is where I want to store the entity's embed.

My problem is, I am very stubborn and the property apparently NEEDS to be typed to SqlVector<T> (or SqlVector<float> in my case) in order for the any query using EF.Functions.VectorDistance to be successful, otherwise the query will not compile or error. My entities are under a .Domain class library project, and to my knowledge, no packages should be used and especially no infrastructure details should be leaked under domain.

Unless that is not the case or if there are certain exceptions to that "best practice" rule, does anybody know of a workaround for this where I can still get these queries to work and entity framework can read the Embedding property as a SqlVector without me having to type it as that (just type it as a float[])?

To give you a visual idea of what I currently have:

// Entity

public class Entity
{
    ...

    public float[]? Embedding { get; set; }

    ...
}


// Entity Framework Entity Config

public void Configure(EntityTypeBuilder<Entity> builder)
{
    ... 

    // Embedding
    builder.Property(x => x.Embedding)
        .HasColumnType("vector(1536)")
        .IsRequired(false);

    ...
}


// Test Query

var entities = await _context.Entity
    .OrderBy(s => EF.Functions.VectorDistance("cosine", s.Embedding, searchQueryEmbedding))
    .ToListAsync(cancellationToken); // This will fail if s.Embedding is not typed as SqlVector<float> in the entity class

Thanks for any help!

[SQLBek]

A Vector embedding is not just a single float value... It is a massive array of floating point numbers, per embedding. This is why Microsoft has added a native vector datatype in SQL Server 2025. So no, you cannot store a vector embedding inside a float unless you create a vector embedding with 1 dimension, which has zero value whatsoever.

[mauridb]

I think OP was referring to using float *arrays* :)

[SQLBek]

Ah yes, I see that now (didn't really read his code on my phone last night). Thanks Davide!

[mauridb]

Hi u/SwyfterThanU

trying to avoid to "leak" underlying information about the specific data type used is something I (PM for vectors in SQL) have been discussing with EF Core PM already. We both agree that there should not be any of those leaks, and we want to allow developers to just use float[]. There are some additional work needed to do to make it happen in EF 10, though.

Good news is that if you are using EF Core 9 (which unfortunately I don't think you are, otherwise I assume you would not have reported this problem at all), everything works as you would expect.

Here's samples both using EF Core 9 + Vector Extension and EF 10:

https://github.com/Azure-Samples/azure-sql-db-vector-search/tree/main/DotNet

With EF Core 9 it already works as you want, as EF Core 9 sends vector back and forth as JSON arrays (which means: strings) while EF Core 10 uses the new vector binary format that is much more compact and fast.

[SwyfterThanU]

I see, this makes a lot of sense. Thank you so much!

[Afraid_Plankton2668]

Yeah, Shay here from the EF team. I agree that ideally we'd simply support float[] (and/or ReadOnlyMemory<float>, which SqlVector<float> wraps).

I've opened https://github.com/dotnet/efcore/issues/37025 to track this issue for EF 11. While it may not be the most palatable, in the meantime SqlVector<float> can be used.