apache/druid · error · IAE

An inline input source must provide a format.

Error message

An inline input source must provide a format.

What it means

InlineInputSourceDefn.validate requires that an inline external table specifies an input format. Inline data is raw text parsed according to a format, so without one Druid cannot interpret the rows. Thrown as IllegalArgumentException during table validation when inputFormatMap is null.

Source

Thrown at server/src/main/java/org/apache/druid/catalog/model/table/InlineInputSourceDefn.java:80

  protected List<ParameterDefn> adHocTableFnParameters()
  {
    return Collections.singletonList(
        new Parameter(DATA_PROPERTY, ParameterType.VARCHAR_ARRAY, false)
    );
  }

  @Override
  public TableFunction partialTableFn(ResolvedExternalTable table)
  {
    return new PartialTableFunction(table, Collections.emptyList());
  }

  @Override
  public void validate(ResolvedExternalTable table)
  {
    // For inline, format is required to match the data
    if (table.inputFormatMap == null) {
      throw new IAE("An inline input source must provide a format.");
    }
    if (CollectionUtils.isNullOrEmpty(table.resolvedTable().spec().columns())) {
      throw new IAE("An inline input source must provide one or more columns");
    }

    super.validate(table);
  }

  @Override
  protected void convertArgsToSourceMap(Map<String, Object> jsonMap, Map<String, Object> args)
  {
    jsonMap.put(InputSource.TYPE_PROPERTY, InlineInputSource.TYPE_KEY);
    List<String> data = CatalogUtils.getStringArray(args, DATA_PROPERTY);

    // Would be nice, from a completeness perspective, for the inline data
    // source to allow zero rows of data. However, such is not the case.
    if (CollectionUtils.isNullOrEmpty(data)) {
      throw new IAE(

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Add an input format (e.g. {"type":"csv"}) to the inline table spec
2. Verify the table JSON includes a non-empty format section before submitting
3. Use validation tooling or the catalog API to check the spec before save

Example fix

// before
{"source":{"type":"inline","data":"a,b"}}
// after
{"source":{"type":"inline","data":"a,b"},"format":{"type":"csv"}}

if (spec.getSource().getType().equals("inline") && spec.getInputFormatMap() == null) {
  throw new IllegalArgumentException("inline source requires an input format");
}

try { defn.validate(table); } catch (IAE e) { if (e.getMessage().contains("must provide a format")) { /* add format to spec */ } else { throw e; } }

When it happens

Trigger: Validating (validate) a ResolvedExternalTable of inline type whose resolved table spec has no input format map — e.g. table created without a format property or with an empty format section.

Common situations: Creating an inline table in the catalog and forgetting the format property; copying an inline source snippet without its format block; a UI/API client that omits format when columns are provided.

Understand the failure class

Background: "is required", "must be set", "missing required field": configuration validation errors across open-source libraries — this error's family across 36 libraries.

Related errors

• An inline input source must provide one or more columns
• An inline table requires one or more rows of data in the '%s
• A local input source requires one property of %s or %s
• '%s' must be a string or an array of strings
• S3 requires one of %s, %s or %s

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/7e1b6459466d0fd3. Report an issue: GitHub.