OpenAPITools/openapi-generator · error · IllegalArgumentException

Invalid model property naming '{name}'. Must be 'original',

Error message

Invalid model property naming '{name}'. Must be 'original', 'camelCase', 'PascalCase' or 'snake_case'

What it means

Defensive default arm inside getNameUsingModelPropertyNaming of the plain javascript generator: it rewrites property names according to the configured convention. The switch covers exactly the MODEL_PROPERTY_NAMING_TYPE constants (original, camelCase, PascalCase, snake_case), so the default arm is effectively unreachable — invalid values are rejected earlier by setModelPropertyNaming (JavascriptClientCodegen.java:639) or by valueOf(). The message prints the property name being converted instead of the bad convention, which is misleading.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavascriptClientCodegen.java:487

    }

    @Override
    public String toModelTestFilename(String name) {
        return toModelName(name) + ".spec";
    }

    private String getNameUsingModelPropertyNaming(String name) {
        switch (CodegenConstants.MODEL_PROPERTY_NAMING_TYPE.valueOf(getModelPropertyNaming())) {
            case original:
                return name;
            case camelCase:
                return camelize(name, LOWERCASE_FIRST_LETTER);
            case PascalCase:
                return camelize(name);
            case snake_case:
                return underscore(name);
            default:
                throw new IllegalArgumentException("Invalid model property naming '" +
                        name + "'. Must be 'original', 'camelCase', " +
                        "'PascalCase' or 'snake_case'");
        }
    }

    @Override
    public String toVarName(String name) {
        // obtain the name from nameMapping directly if provided
        if (nameMapping.containsKey(name)) {
            return nameMapping.get(name);
        }

        // sanitize name
        name = sanitizeName(name);  // FIXME parameter should not be assigned. Also declare it as "final"

        if ("_".equals(name)) {
            name = "_u";
        }

View on GitHub (pinned to fcec517be3)

Solutions

Check your `modelPropertyNaming` value — the setter at JavascriptClientCodegen.java:639 is the realistic source of this message.
Use exactly original, camelCase, PascalCase, or snake_case.
Set the convention only through the setter / additionalProperties, never by field access in subclasses.

Example fix

# before
openapi-generator-cli generate -g javascript -i api.yaml -p modelPropertyNaming=Pascal_Case
# after
openapi-generator-cli generate -g javascript -i api.yaml -p modelPropertyNaming=PascalCase

Defensive patterns

Strategy: validation

Validate before calling

# validate the option — the default branch here is defensive; the setter is the real gate
mpn="${MODEL_PROPERTY_NAMING:-camelCase}"
case "$mpn" in
  original|camelCase|PascalCase|snake_case) ;;
  *) echo "modelPropertyNaming must be original|camelCase|PascalCase|snake_case, got: $mpn" >&2; exit 2 ;;
esac
openapi-generator-cli generate -g javascript -i api.yaml -p modelPropertyNaming="$mpn"

Type guard

private static final java.util.Set<String> NAMING_CONVENTIONS =
        java.util.Set.of("original", "camelCase", "PascalCase", "snake_case");

boolean isValidNamingConvention(String v) {
    return v != null && NAMING_CONVENTIONS.contains(v);
}

Try / catch

try {
    new DefaultGenerator().opts(clientOptInput).generate();
} catch (RuntimeException e) {
    failBuild("javascript generator naming config rejected: " + e.getMessage());
}

Prevention

Check the modelPropertyNaming value first when this wording appears; the setter throw site is the realistic source.
Use the four-constant allowlist in your build script.
Never assign the convention by field access in subclasses.

When it happens

Trigger: Not reachable via supported inputs: `-p modelPropertyNaming=<bad>` fails first in the setter. Only subclasses assigning the modelPropertyNaming field directly, or a future enum constant without a matching case, could land here.

Common situations: Almost never fires; developers hitting this text usually did so via the identically-worded setter error caused by a misspelled modelPropertyNaming value.

Related errors

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/26acfe6792ad2c94. Report an issue: GitHub.