dotnet/efcore · error · ArgumentException

The number of elements ({elementCount}) must match the numbe

Error message

The number of elements ({elementCount}) must match the number of collection-index entries ({collectionIndicesCount}) when creating a RelationalJsonIndex.

What it means

Thrown by the RelationalJsonIndex constructor when the `elements` list and the `collectionIndices` list have different lengths. These two arguments must be parallel (one collection-index path per indexed JSON element), so a mismatch indicates the caller built the index metadata incorrectly.

Source

Thrown at src/EFCore.Relational/Metadata/RelationalJsonIndex.cs:43

public sealed class RelationalJsonIndex : IEquatable<RelationalJsonIndex>
{
    /// <summary>
    ///     Creates a new <see cref="RelationalJsonIndex" /> instance.
    /// </summary>
    /// <param name="elements">The JSON elements targeted by the index, one per indexed property.</param>
    /// <param name="collectionIndices">
    ///     The complex-collection indices traversed to reach each indexed property, parallel to
    ///     <paramref name="elements" />.
    /// </param>
    public RelationalJsonIndex(
        IReadOnlyList<IRelationalJsonElement> elements,
        IReadOnlyList<IReadOnlyList<int?>?>? collectionIndices)
    {
        Check.NotNull(elements);

        if (collectionIndices is not null && elements.Count != collectionIndices.Count)
        {
            throw new ArgumentException(
                RelationalStrings.JsonPathIndexElementsCollectionIndicesMismatch(elements.Count, collectionIndices.Count),
                nameof(collectionIndices));
        }

        Elements = elements;
        CollectionIndices = collectionIndices;
    }

    /// <summary>
    ///     Gets the JSON elements targeted by the index, one per indexed property.
    /// </summary>
    public IReadOnlyList<IRelationalJsonElement> Elements { get; }

    /// <summary>
    ///     Gets the complex-collection indices traversed to reach each indexed property.
    /// </summary>
    public IReadOnlyList<IReadOnlyList<int?>?>? CollectionIndices { get; }

View on GitHub (pinned to dbf9771522)

Solutions

1. Ensure `collectionIndices` has exactly one entry per element in `elements` (or pass `null` when no complex collections are traversed).
2. If you are a provider author, audit the call site that builds `RelationalJsonIndex` and produce a parallel list.
3. Add a unit test asserting `elements.Count == collectionIndices.Count` before construction.

Example fix

// before
new RelationalJsonIndex(elements, collectionIndices); // lengths differ
// after
Debug.Assert(collectionIndices == null || collectionIndices.Count == elements.Count);
new RelationalJsonIndex(elements, collectionIndices);

// Before constructing RelationalJsonIndex (provider/metadata code):
if (collectionIndices is not null && collectionIndices.Count != elements.Count)
    throw new ArgumentException($"collectionIndices ({collectionIndices.Count}) must be parallel to elements ({elements.Count}).");
var index = new RelationalJsonIndex(elements, collectionIndices);

bool IsParallel(IReadOnlyList<IRelationalJsonElement> elements, IReadOnlyList<IReadOnlyList<int?>?>? ci)
    => ci is null || ci.Count == elements.Count;

When it happens

Trigger: Constructing `new RelationalJsonIndex(elements, collectionIndices)` where `collectionIndices.Count != elements.Count`. This is internal/provider-level metadata construction reached when a provider builds a relational index over a JSON-mapped column and supplies a mismatched number of collection-index paths.

Common situations: Writing a custom relational provider or extending JSON-index mapping; a bug in provider JSON-index codegen that emits collection indices for only some indexed properties; mismatched arrays after refactoring index columns.

Related errors

• Model building is not supported when publishing with NativeA
• {numSortOrderProperties} values were provided in CreateIndex
• Invalid token type: '{tokenType}'.
• Relational-specific methods can only be used when the contex
• Timeout must be greater than or equal to zero. Provided time

AI-assisted analysis of dotnet/efcore@dbf9771522 (2026-08-06). Data as JSON: /api/errors/2f085c617a8fb63d. Report an issue: GitHub.