gatsbyjs/gatsby · error · Error

The argument to the `in` predicate should be an array

Error message

The argument to the `in` predicate should be an array

What it means

When the LMDB query planner turns a filter into an index range, the `in` predicate must have an Array value to produce a multi-range scan. A non-array `in` value is rejected at plan time (the in-memory runner has a parallel check) before any range is built.

Source

Thrown at packages/gatsby/src/datastore/lmdb/query/filter-using-index.ts:505

}

function resolveIndexFieldRanges(
  context: IFilterContext,
  query: DbQuery,
  [field, sortDirection]: [fieldName: string, sortDirection: number]
): {
  rangeStarts: RangeBoundary
  rangeEndings: RangeBoundary
} {
  // Tracking starts and ends separately instead of doing Array<[start, end]>
  //  to simplify cartesian product creation later
  const rangeStarts: RangeBoundary = []
  const rangeEndings: RangeBoundary = []

  const filter = getFilterStatement(query)

  if (filter.comparator === DbComparator.IN && !Array.isArray(filter.value)) {
    throw new Error("The argument to the `in` predicate should be an array")
  }

  context.usedQueries.add(query)

  switch (filter.comparator) {
    case DbComparator.EQ:
    case DbComparator.IN: {
      const arr = Array.isArray(filter.value)
        ? [...filter.value]
        : [filter.value]

      // Sort ranges by index sort direction
      arr.sort((a: any, b: any): number => {
        if (a === b) return 0
        if (sortDirection === 1) return a > b ? 1 : -1
        return a < b ? 1 : -1
      })

View on GitHub (pinned to 8b06340921)

Solutions

1. Make the `in` value an array.
2. Type the GraphQL variable as a list.
3. If a single match is intended, use `eq` instead of `in`.

Example fix

// before
filter: { slug: { in: "about" } }
// after
filter: { slug: { in: ["about"] } }

function asArray<T>(v: T | T[]): T[] { return Array.isArray(v) ? v : [v] }
// filter: { slug: { in: asArray(slugs) } }

function isInPredicateValue(v: unknown): v is unknown[] { return Array.isArray(v) }

When it happens

Trigger: A query using an index whose `in` filter value is a scalar; a GraphQL variable mis-typed as `ID` instead of `[ID]`.

Common situations: Same misuse as the in-memory `$in` check, but surfaced when the field has an index that the planner chooses.

Related errors

• ${filter.comparator} value must not be an array
• Range filter ${predicate} should not have array value
• Range filter ${predicate} should not have value of type ${ty
• Bad filter value for predicate ${filter.comparator}: ${inspe
• The $regex comparator is expecting the regex as a string, no

AI-assisted analysis of gatsbyjs/gatsby@8b06340921 (2026-08-13). Data as JSON: /api/errors/42ef1b289700de6f. Report an issue: GitHub.