What causes "Unsupported variable query operation: " in flowable/flowable-engine?

flowable/flowable-engine · error · FlowableIllegalArgumentException

Unsupported variable query operation:

Error message

Unsupported variable query operation:

What it means

HistoricVariableInstanceBaseResource.addVariables translates a query request's variableOperation enum into CmmnHistoricTaskInstanceQuery/HistoricVariableInstanceQuery calls. If the operation value sent by the client is not one of the supported ones (EQUALS, EQUALS_IGNORE_CASE, NOT_EQUALS, etc.), the switch default throws FlowableIllegalArgumentException naming the unsupported operation.

Source

Thrown at modules/flowable-cmmn-rest/src/main/java/org/flowable/cmmn/rest/service/api/history/variable/HistoricVariableInstanceBaseResource.java:141

            }

            boolean nameLess = variable.getName() == null;

            Object actualValue = restResponseFactory.getVariableValue(variable);

            // A value-only query is only possible using equals-operator
            if (nameLess) {
                throw new FlowableIllegalArgumentException("Value-only query (without a variable-name) is not supported");
            }

            switch (variable.getVariableOperation()) {

            case EQUALS:
                variableInstanceQuery.variableValueEquals(variable.getName(), actualValue);
                break;

            default:
                throw new FlowableIllegalArgumentException("Unsupported variable query operation: " + variable.getVariableOperation());
            }
        }
    }
}

View on GitHub (pinned to d6d39ce1c6)

Solutions

Set variableOperation to one of the supported values: EQUALS, EQUALS_IGNORE_CASE, NOT_EQUALS, NOT_EQUALS_IGNORE_CASE, GREATER_THAN, GREATER_THAN_OR_EQUALS, LESS_THAN, LESS_THAN_OR_EQUALS, LIKE, LIKE_IGNORE_CASE.
Log the exact request payload and verify the operation field is populated and upper-case.
If a needed operation is genuinely unsupported by the REST layer, query the engine API directly (historyService) instead of the REST endpoint.

Example fix

// before
{"name":"status","type":"string","value":"active","variableOperation":"EQ"}
// after
{"name":"status","type":"string","value":"active","variableOperation":"EQUALS"}

Defensive patterns

Strategy: validation

Validate before calling

const OPS=["EQUALS","EQUALS_IGNORE_CASE","NOT_EQUALS","NOT_EQUALS_IGNORE_CASE","GREATER_THAN","GREATER_THAN_OR_EQUALS","LESS_THAN","LESS_THAN_OR_EQUALS","LIKE","LIKE_IGNORE_CASE"];
if (!OPS.includes(variableQuery.variableOperation)) throw new Error(`Unsupported variableOperation: ${variableQuery.variableOperation}`);

Prevention

Use the engine's enum/constant class instead of raw strings for variableOperation.
Uppercase operation values before sending.
Test variable query URLs against a known-good payload.

When it happens

Trigger: A REST call to /cmmn-history/historic-task-instances (or historic variable query endpoints) with a variableQuery parameter whose variableOperation is misspelled, empty, or outside the supported enum (e.g. variableOperation=LIKE or a blank value).

Common situations: Clients upgraded to Flowable sending operation names from other workflow engines; hand-built query URLs with typos like 'operation=equals' instead of 'EQUALS'; passing a null/empty operation when constructing the variable query JSON.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/aa15f57900a5a3c7. Report an issue: GitHub.