OpenAPITools/openapi-generator · error · RuntimeException

The BLOB, TEXT, GEOMETRY, and JSON data types cannot be assi

Error message

The BLOB, TEXT, GEOMETRY, and JSON data types cannot be assigned a default value

What it means

PostgreSQL does not allow DEFAULT values on BYTEA, TEXT, GEOMETRY, JSON and JSONB columns (expression defaults like DEFAULT '{}'::jsonb are a separate SQL feature the generator does not emit). When PostgresqlSchemaCodegen's default-processing switch is handed a `default` for any of those types, it throws a RuntimeException (PostgresqlSchemaCodegen.java:1176) rather than generate invalid DDL; all other types fall through and record the default.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PostgresqlSchemaCodegen.java:1176

                    defaultMap.put("isNumeric", false);
                    defaultMap.put("isKeyword", true);

                } else {
                    defaultMap.put("defaultValue", defaultValue);
                    defaultMap.put("isString", true);
                    defaultMap.put("isNumeric", false);
                    defaultMap.put("isKeyword", false);

                }
                return defaultMap;
            case "BYTEA":
            case "TEXT":
            case "GEOMETRY":
            case "JSON":
            case "JSONB":
                // The BLOB, TEXT, GEOMETRY, and JSON data types cannot be assigned a default
                // value.
                throw new RuntimeException(
                        "The BLOB, TEXT, GEOMETRY, and JSON data types cannot be assigned a default value");
            default:
                defaultMap.put("defaultValue", defaultValue);
                defaultMap.put("isString", true);
                defaultMap.put("isNumeric", false);
                defaultMap.put("isKeyword", false);

                return defaultMap;
        }
    }

    /**
     * Finds best fitted PostgreSQL data type for integer variable based on minimum
     * and maximum properties
     *
     * @param minimum  (optional) codegen property
     * @param maximum  (optional) codegen property
     * @param unsigned (optional) whether variable is unsigned or not

View on GitHub (pinned to fcec517be3)

Solutions

Remove the `default` from the offending property in the spec.
Add expression defaults (e.g. DEFAULT '{}'::jsonb) via a hand-maintained migration on top of the generated schema.
Or change the column type to one permitting defaults (bounded string → VARCHAR with default).

Example fix

# before (api.yaml)
components:
  schemas:
    Profile:
      properties:
        prefs:
          type: object
          default: {"newsletter": true}
# after
components:
  schemas:
    Profile:
      properties:
        prefs:
          type: object

Defensive patterns

Strategy: validation

Validate before calling

// postgresql: reject defaults on properties mapping to BYTEA/TEXT/JSON/JSONB/GEOMETRY
for (var e : openAPI.getComponents().getSchemas().entrySet()) {
  Map<String, Schema> props = e.getValue().getProperties();
  if (props == null) continue;
  for (var p : props.entrySet()) {
    Schema s = p.getValue();
    boolean bytea = "string".equals(s.getType()) && "binary".equals(s.getFormat());
    boolean json = "object".equals(s.getType());
    boolean text = "string".equals(s.getType()) && s.getMaxLength() == null;
    if (s.getDefault() != null && (bytea || json || text)) {
      throw new IllegalArgumentException("PostgreSQL DEFAULT not allowed on BYTEA/TEXT/JSON property '"
          + p.getKey() + "' in '" + e.getKey() + "'");
    }
  }
}

Try / catch

try {
    new DefaultGenerator().opts(clientOptInput).generate();
} catch (RuntimeException e) {
    throw new BuildException("PostgreSQL schema generation failed: " + e.getMessage(), e);
}

Prevention

Use `example:` for illustrative values; only use `default:` on types PostgreSQL allows defaults on.
Set maxLength on long strings so they map to VARCHAR rather than TEXT.
Keep JSONB expression defaults in manual migrations layered over generated DDL.

When it happens

Trigger: Generating SQL with the postgresql generator from a spec where a property mapped to BYTEA (format: binary), TEXT (long unbounded string), JSON/JSONB (type: object, or string with x-postgres-type json/jsonb), or GEOMETRY has a non-null `default`.

Common situations: Designing the API spec and DB schema from one source; carrying sample/default payload values from API docs into schema generation; migrating from a generator that ignored unsupported defaults to one that fails fast.

Related errors

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/c254f9355986c644. Report an issue: GitHub.