(DataFlex) Execution Plan Failure Due to Circular Dependencies

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This example demonstrates what happens when an execution plan cannot be created due to a cycle in the dependency graph.

The target curl command requires {{report_id}}. A helper function is defined to produce report_id, but it depends on user_id. In turn, user_id depends on account_id, and account_id depends back on report_id.

This creates a circular dependency:

• report_id → user_id
• user_id → account_id
• account_id → report_id

Because each required value ultimately depends on itself, there is no starting point with a known or independently resolvable input. As a result, it is impossible to construct a valid execution plan.

When ExaminePlan is called, it detects this cycle and reports that the execution plan cannot be created.

This example highlights that dependency resolution requires an acyclic graph. Every chain of dependencies must eventually terminate in a known value. If a cycle exists, the system correctly identifies it and prevents execution.

Note: This example requires Chilkat v11.5.0 or greater.

For more information, see https://www.chilkatsoft.com/curl_dependency_engine.asp

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoHttpCurl
    String sTargetCurl
    String sFnName
    Variant vPlanJson
    Handle hoPlanJson
    String sTemp1

    Move False To iSuccess

    Get Create (RefClass(cComChilkatHttpCurl)) To hoHttpCurl
    If (Not(IsComObjectCreated(hoHttpCurl))) Begin
        Send CreateComObject of hoHttpCurl
    End

    // This example uses fake URLs and fake variables to demonstrate a dependency cycle.
    // No requests are sent because we only call ExaminePlan.

    // The target curl command requires {{report_id}}.
    Move "curl -X GET https://api.example.com/reports/{{report_id}}" To sTargetCurl

    // getReportId can produce report_id, but it requires user_id.
    Move "getReportId" To sFnName
    Get ComAddFunction Of hoHttpCurl sFnName "curl -X GET https://api.example.com/report-id?user={{user_id}}" To iSuccess
    Get ComAddOutput Of hoHttpCurl sFnName "report.id" "report_id" To iSuccess

    // getUserId can produce user_id, but it requires account_id.
    Move "getUserId" To sFnName
    Get ComAddFunction Of hoHttpCurl sFnName "curl -X GET https://api.example.com/user-id?account={{account_id}}" To iSuccess
    Get ComAddOutput Of hoHttpCurl sFnName "user.id" "user_id" To iSuccess

    // getAccountId can produce account_id, but it requires report_id.
    // This creates a cycle:
    // 
    //   report_id -> user_id -> account_id -> report_id
    // 
    // In other words:
    //   - targetCurl needs report_id
    //   - report_id requires user_id
    //   - user_id requires account_id
    //   - account_id requires report_id
    // 
    // There is no starting point where the dependency chain can be resolved.
    Move "getAccountId" To sFnName
    Get ComAddFunction Of hoHttpCurl sFnName "curl -X GET https://api.example.com/account-id?report={{report_id}}" To iSuccess
    Get ComAddOutput Of hoHttpCurl sFnName "account.id" "account_id" To iSuccess

    // Examine the execution plan without sending any requests.
    // The plan cannot be created because the dependencies contain a cycle.
    Get Create (RefClass(cComChilkatJsonObject)) To hoPlanJson
    If (Not(IsComObjectCreated(hoPlanJson))) Begin
        Send CreateComObject of hoPlanJson
    End
    Set ComEmitCompact Of hoPlanJson To False

    Get pvComObject of hoPlanJson to vPlanJson
    Get ComExaminePlan Of hoHttpCurl sTargetCurl vPlanJson To iSuccess

    // Success is expected to be false.
    Showln "success = " iSuccess

    Get ComEmit Of hoPlanJson To sTemp1
    Showln sTemp1

    // Expected result:
    // 
    // {
    //   "errors": [{
    //     "variable": "report_id",
    //     "msg": "Cycle detected"
    //   },{
    //     "variable": "account_id",
    //     "msg": "Unable to resolve"
    //   },{
    //     "variable": "user_id",
    //     "msg": "Unable to resolve"
    //   },{
    //     "variable": "report_id",
    //     "msg": "Unable to resolve"
    //   }]
    // 


End_Procedure