dotnet/efcore · error · InvalidOperationException

The type '{clrType}' is being used as a vector, but the vect

Error message

The type '{clrType}' is being used as a vector, but the vector data type cannot be inferred. Only 'ReadOnlyMemory<byte>, ReadOnlyMemory<sbyte>, ReadOnlyMemory<float>, byte[], sbyte[], and float[] are supported.

What it means

Thrown by CosmosVectorType.CreateDefaultVectorDataType when the property CLR type is not ReadOnlyMemory<byte/sbyte/float> or one of the array forms byte[]/sbyte[]/float[]. CreateDefaultVectorDataType unwraps ReadOnlyMemory<> or IEnumerable<> element types and only accepts sbyte/byte/float; anything else (double, long, a custom struct, decimal) throws. The message lists the supported types.

Source

Thrown at src/EFCore.Cosmos/Metadata/Internal/CosmosVectorType.cs:33

{
    /// <summary>
    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
    ///     any release. You should only use it directly in your code with extreme caution and knowing that
    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
    /// </summary>
    public static VectorDataType CreateDefaultVectorDataType(Type clrType)
    {
        var elementType = clrType.TryGetElementType(typeof(ReadOnlyMemory<>))?.UnwrapNullableType()
            ?? clrType.TryGetElementType(typeof(IEnumerable<>))?.UnwrapNullableType();

        return elementType == typeof(sbyte)
            ? VectorDataType.Int8
            : elementType == typeof(byte)
                ? VectorDataType.Uint8
                : elementType == typeof(float)
                    ? VectorDataType.Float32
                    : throw new InvalidOperationException(CosmosStrings.BadVectorDataType(clrType.ShortDisplayName()));
    }
}

View on GitHub (pinned to dbf9771522)

Solutions

1. Change the vector property CLR type to one of ReadOnlyMemory<float>, float[], ReadOnlyMemory<byte>, byte[], ReadOnlyMemory<sbyte>, or sbyte[].
2. If the source data is double/decimal, convert it to float[] before assigning to the entity property.

Example fix

// before
public double[] Embedding { get; set; }
modelBuilder.Entity<Item>().Property(i => i.Embedding)
    .HasVectorDistanceFunction(CosmosVectorDistanceFunction.Cosine)
    .HasVectorDimensions(1536);

// after
public float[] Embedding { get; set; }

static bool IsSupportedVectorClrType(Type t) =>
    t == typeof(float[]) || t == typeof(byte[]) || t == typeof(sbyte[])
    || t == typeof(ReadOnlyMemory<float>) || t == typeof(ReadOnlyMemory<byte>) || t == typeof(ReadOnlyMemory<sbyte>);

static bool IsSupportedVectorClrType(Type t) =>
    t == typeof(float[]) || t == typeof(byte[]) || t == typeof(sbyte[])
    || t == typeof(ReadOnlyMemory<float>) || t == typeof(ReadOnlyMemory<byte>) || t == typeof(ReadOnlyMemory<sbyte>);

When it happens

Trigger: Configuring a vector property with HasVectorDistanceFunction / HasVectorDimensions on a property whose CLR type is e.g. double[], long[], Vector<float>, or a custom struct, then triggering model validation (which calls CreateDefaultVectorDataType).

Common situations: Bringing embeddings stored as double[] from another system. Using a numeric type that the model author assumed was supported. Wrapping vectors in a custom struct for domain clarity.

Related errors

• 'Except' cannot be called on the builder returned by 'HasAut
• The type '{givenType}' cannot be mapped as a dictionary beca
• The value '{value}' provided for argument '{argumentName}' m
• Cosmos-specific methods can only be used when the context is
• The '{methodName}' method is not supported because the query

AI-assisted analysis of dotnet/efcore@dbf9771522 (2026-08-06). Data as JSON: /api/errors/0aef4881e7d8fa55. Report an issue: GitHub.