dotnet/efcore · error · InvalidOperationException

A vector index is defined for `{entityType}.{property}`, but

Error message

A vector index is defined for `{entityType}.{property}`, but this property has not been configured as a vector. Use 'IsVectorProperty()' in 'OnModelCreating' to configure the property as a vector.

What it means

Thrown by ValidateVectorIndex when the single property of a vector index is not an IProperty, or has not been configured as a vector (missing GetVectorDistanceFunction() or GetVectorDimensions()). A property must be marked as a vector via IsVectorProperty(distanceFunction, dimensions) before it can be the target of a vector index.

Source

Thrown at src/EFCore.Cosmos/Infrastructure/Internal/CosmosModelValidator.cs:624

    protected virtual void ValidateVectorIndex(
        IIndex index,
        IDiagnosticsLogger<DbLoggerCategory.Model.Validation> logger)
    {
        var entityType = index.DeclaringEntityType;

        if (index.Properties.Count > 1)
        {
            throw new InvalidOperationException(
                CosmosStrings.CompositeVectorIndex(
                    entityType.DisplayName(),
                    string.Join(",", index.Properties.Select(e => e.Name))));
        }

        if (index.Properties[0] is not IProperty firstVectorIndexProperty
            || firstVectorIndexProperty.GetVectorDistanceFunction() == null
            || firstVectorIndexProperty.GetVectorDimensions() == null)
        {
            throw new InvalidOperationException(
                CosmosStrings.VectorIndexOnNonVector(
                    entityType.DisplayName(),
                    index.Properties[0].Name));
        }
    }

    /// <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>
    protected virtual void ValidateFullTextIndex(
        IIndex index,
        IDiagnosticsLogger<DbLoggerCategory.Model.Validation> logger)
    {
        if (index.Properties.Count > 1)
        {

View on GitHub (pinned to dbf9771522)

Solutions

Configure the property as a vector first: modelBuilder.Entity<E>().Property(e => e.Embedding).IsVectorProperty(DistanceFunction.Cosine, 1536).
Ensure the vector index references the same property that was configured with IsVectorProperty.
Set both distance function and dimensions, since the validator requires both to be non-null.

Example fix

// before
modelBuilder.Entity<Doc>()
    .HasIndex(d => d.Embedding)
    .IsVectorIndex(VectorIndexType.DiskANN);

// after
modelBuilder.Entity<Doc>()
    .Property(d => d.Embedding)
    .IsVectorProperty(DistanceFunction.Cosine, 1536);
modelBuilder.Entity<Doc>()
    .HasIndex(d => d.Embedding)
    .IsVectorIndex(VectorIndexType.DiskANN);

Defensive patterns

Strategy: validation

Validate before calling

using var ctx = new MyContext();
foreach (var e in ctx.Model.GetEntityTypes())
{
    foreach (var idx in e.GetDeclaredIndexes().Where(i => i.GetVectorIndexType() is not null))
    {
        foreach (var p in idx.Properties.OfType<Microsoft.EntityFrameworkCore.Metadata.IProperty>())
        {
            Debug.Assert(p.GetVectorDistanceFunction() is not null && p.GetVectorDimensions() is not null,
                $"{e.Name}.{p.Name} is in a vector index but was not configured with IsVectorProperty()");
        }
    }
}

Try / catch

try { ctx.Model.GetModel(); }
catch (InvalidOperationException ex) when (ex.Message.Contains("has not been configured as a vector"))
{
    logger.LogError(ex, "Vector index targets a property that is not a vector");
    throw;
}

Prevention

Always configure IsVectorProperty(distanceFunction, dimensions) on the property before adding a vector index over it.
Set both distance function and dimensions; the validator requires both.
When renaming a vector property, update both the IsVectorProperty and HasIndex declarations.

When it happens

Trigger: Calling HasIndex(e => e.Embedding).IsVectorIndex(...) on a property that was never configured with IsVectorProperty(...), so VectorDistanceFunction/VectorDimensions are null.

Common situations: Declaring the index before configuring the vector property; forgetting the IsVectorProperty call; renaming the vector property without updating the index.

Related errors

AI-assisted analysis of dotnet/efcore@dbf9771522 (2026-08-06). Data as JSON: /api/errors/6e83b8ce08f047e5. Report an issue: GitHub.