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

CosmosClientWrapper throws CompositeFullTextIndex when building container indexing policy and encounters a full-text index whose index.Properties contains more than one property. Cosmos DB full-text indexes must target exactly one property; composite full-text indexes are not supported.

Solutions

Define the full-text index over exactly one (string) property.
Define a separate single-property full-text index for each searchable string property.

Example fix

// before
modelBuilder.Entity<Doc>()
    .HasIndex(x => new { x.Title, x.Body })
    .IsFullTextIndex();

// after - one full-text index per property
modelBuilder.Entity<Doc>().HasIndex(x => x.Title).IsFullTextIndex();
modelBuilder.Entity<Doc>().HasIndex(x => x.Body).IsFullTextIndex();

Defensive patterns

Strategy: validation

Validate before calling

// At model build, assert full-text indexes target exactly one property.
foreach (var idx in entityType.GetIndexes())
{
    if (idx.IsFullTextIndex() == true && idx.Properties.Count > 1)
        throw new InvalidOperationException($"Full-text index on {entityType.DisplayName()} targets multiple properties.");
}

Type guard

static bool IsSinglePropertyFullTextIndex(IIndex idx) => idx.IsFullTextIndex() == true && idx.Properties.Count == 1;

Prevention

Define full-text indexes over a single string property only.
Add a model-build validator that rejects multi-property full-text indexes.
Review all HasIndex(...).IsFullTextIndex() calls during code review.

When it happens

Trigger: Defining an index over multiple properties and marking it as a full-text index, e.g. modelBuilder.Entity<T>().HasIndex(x => new { x.A, x.B }).IsFullTextIndex().

Common situations: Reusing a composite index definition and applying full-text configuration to all its paths; bulk index configuration.

Related errors

AI-assisted analysis of dotnet/efcore@3a2006ef56 (2026-08-11). Data as JSON: /api/errors/cb9996b3cabaa7d7. Report an issue: GitHub.

Appendix: source

Thrown at src/EFCore.Cosmos/Storage/Internal/CosmosClientWrapper.cs:200

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

                vectorIndexes.Add(
                    new VectorIndexPath { Path = GetJsonPropertyPathFromRoot(index.Properties[0]), Type = vectorIndexType.Value });
                continue;
            }

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

                fullTextIndexPaths.Add(
                    new FullTextIndexPath { Path = GetJsonPropertyPathFromRoot(index.Properties[0]) });
                continue;
            }

            var isConvention = index is IConventionIndex convIndex
                && convIndex.GetConfigurationSource() == ConfigurationSource.Convention;

            if (index.Properties.Count == 1)
            {
                var path = GetJsonPropertyPathFromRoot(index.Properties[0]) + "/?";
                if (seenIncludedPaths.Add(path))
                {

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