gatsbyjs/gatsby · error

Can't determine type for "${value}" in \`${selector}\`.

Error message

Can't determine type for "${value}" in \`${selector}\`.

What it means

Gatsby infers a GraphQL field type from the first observed ("example") value of each node field. getSimpleFieldConfig switches on typeof value to map to Boolean/Int/Float/String/Date/File or a nested object type. When the example value does not match any supported branch (e.g. it is null, undefined, a Symbol, a BigInt, or a Function), no type can be assigned and Gatsby throws with the offending value and the dotted selector path.

Source

Thrown at packages/gatsby/src/schema/infer/add-inferred-fields.js:381

        const inferenceConfig = getInferenceConfig({
          typeComposer: fieldTypeComposer,
          defaults: config,
        })

        return {
          type: addInferredFieldsImpl({
            schemaComposer,
            typeComposer: fieldTypeComposer,
            exampleObject: value,
            typeMapping,
            prefix: selector,
            unsanitizedFieldPath,
            config: inferenceConfig,
          }),
        }
      }
  }
  throw new Error(`Can't determine type for "${value}" in \`${selector}\`.`)
}

const createTypeName = selector => {
  const keys = selector.split(`.`)
  const suffix = keys.slice(1).map(_.upperFirst).join(``)
  return `${keys[0]}${suffix}`
}

const NON_ALPHA_NUMERIC_EXPR = new RegExp(`[^a-zA-Z0-9_]`, `g`)

/**
 * GraphQL field names must be a string and cannot contain anything other than
 * alphanumeric characters and `_`. They also can't start with `__` which is
 * reserved for internal fields (`___foo` doesn't work either).
 */
const createFieldName = key => {
  // Check if the key is really a string otherwise GraphQL will throw.
  invariant(

View on GitHub (pinned to 8b06340921)

Solutions

1. Make the first-observed value of the field a concrete scalar/object (reorder records or backfill a placeholder).
2. Declare the field type explicitly via createTypes schema customization so inference is bypassed.
3. Add an inference rule with omit for the problematic field, or annotate with @dontInfer on the type.
4. Sanitize values in sourceNodes (coerce nulls/BigInts/Symbols to strings) before createNode.

Example fix

// before: field 'price' is null in the first record -> [160]
// after: declare the type explicitly in gatsby-node.js
exports.sourceNodes = ({ actions }) => { /* ... */ }
exports.createSchemaCustomization = ({ actions }) => {
  actions.createTypes(`
    type Product implements Node {
      price: Float
    }
  `)
}

// Before createNode, ensure no field's example value is non-inferrable
const INFERRABLE = ['boolean','number','string','object']
function isInferrableExample(v) {
  if (v === null) return false
  const t = typeof v
  if (!INFERRABLE.includes(t)) return false           // undefined/symbol/function/bigint
  if (t === 'object' && (Array.isArray(v) || v instanceof Date || v instanceof String)) return true
  return true
}
function validateNode(node) {
  for (const [k, v] of Object.entries(node)) {
    if (v === undefined) throw new Error(`Field ${k} is undefined; cannot infer type`)
  }
}

function isInferrableValue(value) {
  if (value === null || value === undefined) return false
  const t = typeof value
  return t === 'boolean' || t === 'number' || t === 'string' ||
    (t === 'object' && (value instanceof Date || value instanceof String || Object.getPrototypeOf(value) === Object.prototype || Object.getPrototypeOf(value) === null))
}

When it happens

Trigger: A source node field whose very first encountered value is null/undefined/BigInt/Symbol/function; an array field whose first element is null; a custom plugin emitting an opaque object that isn't a plain Object/Date/String; the @dontInfer path returning null so no composer is built and execution falls through to the throw.

Common situations: Source plugin records where a field happens to be null in the first row; a plugin returning BigInt ids after a Node.js upgrade; inconsistent data shapes across nodes; moving to a stricter Gatsby inference version.

Related errors

• stringifiedErrors
• Expected non-null field value.
• Expected array field value.
• Building schema failed
• Interfaces with the `nodeInterface` extension must have a fi

AI-assisted analysis of gatsbyjs/gatsby@8b06340921 (2026-08-13). Data as JSON: /api/errors/30679067b378700a. Report an issue: GitHub.