topic Re: Cannot set value of a non-lvalue expression in Alfresco Archive

Cannot set value of a non-lvalue expression

martin_p — Tue, 03 Dec 2013 10:10:13 GMT

Hi,My process has custom widgets associated with formProperties. One of these properties may or not be defined, according to an external condition. My main goal is to be able to pass an information to the FormRenderer so that it is able to decide by itself if it should display or not.I implemented t

Re: Cannot set value of a non-lvalue expression

martin_p — Wed, 04 Dec 2013 09:58:52 GMT

I assume (but I'm not sure) that I am not using "expression" properly.
I use "expression" to provide input variable to a form that is expected to return a completely different output value.
It seems to me that :
<code>
<formProperty … expression=…>
</code>
Should be use to set the form with a default value of the same type than the output value of the form.

Re: Cannot set value of a non-lvalue expression

martin_p — Wed, 04 Dec 2013 10:42:39 GMT

I dived in activiti in debug mode.

The exception happens in FormPropertyHandler while trying to submit form values :
<code>
public void submitFormProperty(ExecutionEntity execution, Map<String, String> properties) {
    if (!isWritable && properties.containsKey(id)) {
      throw new ActivitiException("form property '"+id+"' is not writable");
    }

    if (isRequired && !properties.containsKey(id) && defaultExpression == null) {
      throw new ActivitiException("form property '"+id+"' is required");
    }

    Object modelValue = null;
    if (properties.containsKey(id)) {
      final String propertyValue = properties.remove(id);
      if (type != null) {
        modelValue = type.convertFormValueToModelValue(propertyValue);
      } else {
        modelValue = propertyValue;
      }
    } else if (defaultExpression != null) {
      final Object expressionValue = defaultExpression.getValue(execution);
      if (type != null && expressionValue != null) {
        modelValue = type.convertFormValueToModelValue(expressionValue.toString());
      } else if (expressionValue != null) {
        modelValue = expressionValue.toString();
      } else if (isRequired) {
        throw new ActivitiException("form property '"+id+"' is required");
      }
    }

    if (modelValue != null) {
      if (variableName != null) {
        execution.setVariable(variableName, modelValue);            <<<<<<<<<< where it should go
      } else if (variableExpression != null) {
        variableExpression.setValue(modelValue, execution);        <<<<<<<<<< where it fails
      } else {
        execution.setVariable(id, modelValue);
      }
    }
}
</code>

Reading the code it seams logical : we can't expect to assign the result to an expression.

So I modified the workflow property to define a variable name :
<code>
<activiti:formProperty id="is-responsible" name="responsability" type="is-responsible" variable="is-responsible" expression="${execution.getVariable("flightEventId&quot}"></activiti:formProperty>
</code>

Which at least avoid the crash. Still I got unexpected behaviour so I believe I am not using the workflow properly to do what I expect.

Cheers

Re: Cannot set value of a non-lvalue expression

trademak — Wed, 04 Dec 2013 15:06:06 GMT

Just using a value attribute with a value like "${flightEventId}" would be sufficient. That will retrieve the value from the execution.

Best regards,

Re: Cannot set value of a non-lvalue expression

martin_p — Wed, 04 Dec 2013 15:58:58 GMT

Thanks for your suggestion.
Unfortunately it does not work, even with a new process instance.

As you suggest I changed the workflow to :
<code>
<activiti:formProperty id="is-responsible" name="responsability" type="is-responsible" value="${flightEventId}">
</code>

Breaking into Activiti code, I noticed that the below modelValue variable remains null
<java>
public FormProperty createFormProperty(ExecutionEntity execution) {
    FormPropertyImpl formProperty = new FormPropertyImpl(this);
    Object modelValue = null;

    if (execution!=null) {
      if (variableName != null || variableExpression == null) {
        final String varName = variableName != null ? variableName : id;
        if (execution.hasVariable(varName)) {
          modelValue = execution.getVariable(varName);
        } else if (defaultExpression != null) {
          modelValue = defaultExpression.getValue(execution);
        }
      } else {
        modelValue = variableExpression.getValue(execution);
      }
    } else {
      // Execution is null, the form-property is used in a start-form. Default value
      // should be available (ACT-1028) even though no execution is available.
      if (defaultExpression != null) {
        modelValue = defaultExpression.getValue(StartFormVariableScope.getSharedInstance());
      }
    }
                                      <<<<<<<<<<<<<<< AT THIS POINT MODELVALUE IS STILL NULL
    if (modelValue instanceof String) {
      formProperty.setValue((String) modelValue);
    } else if (type != null) {
      String formValue = type.convertModelValueToFormValue(modelValue);
      formProperty.setValue(formValue);
    } else if (modelValue != null) {
      formProperty.setValue(modelValue.toString());
    }

    return formProperty;
}
</java>