(DataFlex) Impossible Execution Plan

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This example demonstrates what happens when it is not possible to construct an execution plan due to missing dependencies.

The target curl command requires a {{drive_id}} value. However, no variable named drive_id has been defined, and no helper function is registered that can produce it. Although a helper function (getSite) is defined, it only produces site_id, which does not satisfy the requirement.

When ExaminePlan is called, it reports that the execution plan cannot be created because a required input is missing and no function exists to provide it.

When DoYourThing is called, it fails for the same reason. The failure is not due to a network or HTTP error, but because the dependency graph cannot be resolved. The FailReason property indicates this condition with a specific error code.

This example highlights that for an execution plan to be valid, every required input must either:

• Already have a defined value, or
• Be producible by a defined curl function with resolvable inputs

If neither condition is met, the system correctly detects the unresolved dependency 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
    Integer iTemp1

    Move False To iSuccess

    Move False To iSuccess

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

    // This target curl command requires {{drive_id}}.
    Move "curl -X GET https://graph.microsoft.com/v1.0/drives/{{drive_id}}/root/children" To sTargetCurl

    // Define a helper function that can produce site_id.
    // However, it does NOT produce drive_id.
    Move "getSite" To sFnName
    Get ComAddFunction Of hoHttpCurl sFnName "curl -X GET https://graph.microsoft.com/v1.0/sites/root:/sites/{{site_name}}" To iSuccess
    Get ComAddOutput Of hoHttpCurl sFnName "id" "site_id" To iSuccess

    // Provide site_name, so getSite can run.
    Send ComSetVar To hoHttpCurl "site_name" "test"

    // Try to examine the execution plan.
    // This fails because {{drive_id}} is required by the target curl command,
    // but drive_id is not already known and no defined function produces it.
    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
    If (iSuccess = False) Begin
        // Should equal 5.
        Get ComFailReason Of hoHttpCurl To iTemp1
        Showln "ExaminePlan fail reason = " iTemp1

        // Examine the error(s) returned in planJson
        Get ComEmit Of hoPlanJson To sTemp1
        Showln sTemp1

        // Expected output:
        // {
        //   "errors": [{
        //     "variable": "drive_id",
        //     "msg": "No candidate functions"
        //   }]
        // }
    End

    // DoYourThing will fail for the same reason.
    Get ComDoYourThing Of hoHttpCurl sTargetCurl To iSuccess

    // We expect DoYourThing to fail because it is not possible to construct
    // a valid execution plan (drive_id cannot be resolved).
    If (iSuccess = False) Begin
        // FailReason provides a numeric code indicating why the operation failed.
        // A value of 5 specifically means that an execution plan could not be created
        // due to unresolved dependencies (i.e., a required variable has no source).
        Get ComFailReason Of hoHttpCurl To iTemp1
        Showln "DoYourThing fail reason = " iTemp1
    End
    Else Begin
        // If execution succeeds, it means the plan was somehow resolved,
        // which would be unexpected in this scenario.
        Showln "Unexpected success."
    End



End_Procedure