dotnet/efcore · error · InvalidOperationException

A full-text index on

Error message

A full-text index on '{entityType}' is defined over multiple properties (`{properties}`). A full-text index can only target a single property.

What it means

Thrown by CosmosModelValidator.ValidateFullTextIndex when a full-text index is declared over more than one property. Azure Cosmos DB full-text indexes can target exactly one property each, so the validator rejects any composite full-text index at model validation time.

Solutions

Split the composite full-text index into one single-property full-text index per property.
If you need combined search across multiple fields, query each indexed property separately or project/concatenate at the application layer.
Re-run with the corrected model to confirm validation passes.

Example fix

// before
modelBuilder.Entity<Article>()
    .HasIndex(a => new { a.Title, a.Body })
    .HasFullTextIndex();

// after
modelBuilder.Entity<Article>(b =>
{
    b.HasIndex(a => a.Title).HasFullTextIndex();
    b.HasIndex(a => a.Body).HasFullTextIndex();
});

Defensive patterns

Strategy: validation

Validate before calling

// Reject any full-text index whose property count != 1 at startup.
foreach (var et in modelBuilder.Model.GetEntityTypes())
foreach (var idx in et.GetIndexes())
    if (idx.IsFullTextIndex() && idx.Properties.Count != 1)
        throw new InvalidOperationException($"Full-text index on {et.DisplayName()} must target a single property.");

Prevention

Define full-text indexes one property at a time; never compose them.
Review any .HasIndex(new { ... }) builder before chaining .HasFullTextIndex().
Codify the single-property rule in a test that scans GetIndexes().

When it happens

Trigger: Calling HasFullTextIndex on an index whose Properties list contains 2+ properties (e.g. composing an index over (Title, Body) and marking it full-text).

Common situations: Porting a relational composite full-text index to Cosmos; combining multiple string properties into one index assuming it behaves like SQL Server's full-text catalog.

Related errors

AI-assisted analysis of dotnet/efcore@3a2006ef56 (2026-08-11). Data as JSON: /api/errors/5ec1c6005a197581. Report an issue: GitHub.

Appendix: source

Thrown at src/EFCore.Cosmos/Infrastructure/Internal/CosmosModelValidator.cs:643

                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)
        {
            throw new InvalidOperationException(
                CosmosStrings.CompositeFullTextIndex(
                    index.DeclaringEntityType.DisplayName(),
                    string.Join(",", index.Properties.Select(e => e.Name))));
        }

        if (index.Properties[0] is not IProperty firstFullTextProperty
            || firstFullTextProperty.GetIsFullTextSearchEnabled() != true)
        {
            throw new InvalidOperationException(
                CosmosStrings.FullTextIndexOnNonFullTextProperty(
                    index.DeclaringEntityType.DisplayName(),
                    index.Properties[0].Name,
                    nameof(CosmosPropertyBuilderExtensions.EnableFullTextSearch)));
        }
    }

    /// <summary>
    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to

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