IMsCalculationChainIterator.Expression

Syntax

Description

The Expression property returns cycle calculation condition.

Comments

To set up condition calculation options, use the IMsCalculationChainIterator.Transform property.

To limit the number of cycle iterations, use the IMsCalculationChainIterator.MaxIterations property.

To enable one-time cycle execution without checking of condition, use the IMsCalculationChainIterator.PostCondition property.

Example

Executing the example requires that the repository contains a modeling container with the MS identifier that contains a metamodel with the METAMODEL_ITERATOR identifier.

Add links to the Metabase and Ms system assemblies.

Sub UserProc;
Var
    mb: IMetabase;
    MsKey: Integer;
    MetaModel: IMsMetaModel;
    Param: IMsModelParam;
    CalcChain: IMsCalculationChainEntries;
    Iterator: IMsCalculationChainIterator;
    Model: IMsModel;
    Trans, IterTrans: IMsFormulaTransform;
    Slice: IMsFormulaTransformSlice;
    Selector: IMsFormulaTransformSelector;
    Formula: IMsFormula;
    TransformVar: IMsFormulaTransformVariable;
    Determ: IMsDeterministicTransform;
    Expr: IExpression;
Begin
    mb := MetabaseClass.Active;
    // Get modelling container key
    MsKey := mb.GetObjectKeyById("MS");
    // Get metamodel
    MetaModel := mb.ItemByIdNamespace("METAMODEL_ITERATOR", MsKey).Edit As IMsMetaModel;
    // Clear all metamodel parameters
    MetaModel.Params.Clear;
    // Add a new parameter
    Param := MetaModel.Params.Add;
    Param.DefaultValue := 0;
    Param.Id := "THRESHOLD";
    Param.Name := "THRESHOLD";
    // Clear metamodel calculation chain
    CalcChain := MetaModel.CalculationChain;
    CalcChain.Clear;
    // Create a cycle in metamodel calculation chain
    Iterator := CalcChain.AddIterator("While/Repeat");
    // Set cycle execution condition
    Iterator.PostCondition := True;
    Iterator.MaxIterations := 600;
    Expr := Iterator.Expression;
    Expr.AsString := "{THRESHOLD}<5";
    If Expr.ErrorInfo <> Null Then
        Debug.WriteLine(Expr.ErrorInfo.ErrorMessage);
    End If;
    // Set condition calculation mode
    IterTrans := Iterator.Transform;
    IterTrans.CalculationType := MsCalculationType.Pointwise;
    IterTrans.CalculationDirection := MsCalculationDirection.Forward;
    // Set internal model in metamodel calculation chain
    Model := Iterator.Contents.AddExclusiveModel.EditModel;
    Model.AutoName := True;
    // Set model calculation parameters
    Trans := Model.Transform;
    Trans.CalculationType := MsCalculationType.Pointwise;
    Trans.CalculationDirection := MsCalculationDirection.Forward;
    // Specify the THRESHOLD parameter as a modeling variable
    TransformVar := Trans.Outputs.AddParamVariable("THRESHOLD");
    Slice := TransformVar.Slices.Add(Null);
    Selector := Trans.CreateSelector;
    Selector.Slice := Slice;
    Formula := Trans.Transform(Selector);
    Formula.Kind := MsFormulaKind.Deterministic;
    Determ := Formula.Method As IMsDeterministicTransform;
    // Set model calculation formula
    Expr := Determ.Expression;
    Expr.AsString := "{THRESHOLD}+RandBetween(-2,3)";
    If Expr.ErrorInfo <> Null Then
        Debug.WriteLine(Expr.ErrorInfo.ErrorMessage);
    End If;
    // Save metamodel
    (MetaModel As IMetabaseObject).Save;
End Sub UserProc;

After executing the example a cycle is created in the metamodel that is executed until the THRESHOLD value is less than 5. If the condition is not executed during 600 iterations, the cycle is finished.