Extend the list of Electronic reporting (ER) functions

Various types of functions are supported in Electronic reporting (ER) expressions for data transformation – text, date and time, mathematical logical, information, data type conversion, and other (business domain–specific functions). In addition to built-in functions, ER lets you extend the list of available functions. This article includes an overview of key tasks that you must complete to introduce a new function.

All ER functions in application code are represented as classes that extend the ERExpression class. Two types of functions are recognized:

• Fixed number of arguments – These functions are represented by classes that include methods that have the prefix parm (see parmInput, parmStartNum in the sample code the follows). The order of arguments is set by the SysOperationDisplayOrderAttribute attribute.
• Variable number of arguments – These functions (see the ERExpressionGenericCase class) are represented by classes that implement the ERIObjectContainer interface. An additional Add method is used to declare the types that a function accepts.

Here are the recommended steps for introducing a new function for ER expressions:

• Select a base class for your function, based on the return value type (see ERExpressionString in the sample code that follows).

  • Create a new class that extends the selected class (see ERExpressionStringMid in the sample code the follows).

    • Provide required attributes:

      • SysOperationLabelAttribute – This attribute defines the function’s name.
      • SysOperationHelpTextAttribute – This attribute defines the function’s Help text.
      • ERComponentGroupAttribute – This attribute defines the group that the function belongs to. (For more information, see Formula designer in Electronic reporting (ER).)

    • Provide arguments:

      • For a fixed number of arguments function, provide methods that have the prefix parm, and use the SysOperationDisplayOrderAttribute attribute to set the order of the arguments.
      • For a variable number of argument function, implement the ERIObjectContainer interface.

    • Provide an evaluation method.

Here is an example.

/// <summary>
/// Returns the characters from the middle of a text string, given a starting position and length.
/// </summary>
[
    SysOperationLabelAttribute ('MID'),
    SysOperationHelpTextAttribute ("@ElectronicReporting:ExpressionStringMidHelpText"),
    ERComponentGroupAttribute ("@ElectronicReporting:String")
]
class ERExpressionStringMid extends ERExpressionString
{
    ERExpressionString input;
    ERExpressionInt startNum;
    ERExpressionInt numChars;
    public str evaluateString(ERIDataContext _dataContext)
    {
        return subStr(
            this.parmInput().evaluateString(_dataContext),
            this.parmStartNum().evaluateInt(_dataContext),
            this.parmNumChars().evaluateInt(_dataContext));
    }
    [DataMemberAttribute, SysOperationLabelAttribute ("@ElectronicReporting:Input"), SysOperationDisplayOrderAttribute ("1")]
    public ERExpressionString parmInput(ERExpressionString _input = input)
    {
        input = _input;
        return input;
    }
    [DataMemberAttribute, SysOperationLabelAttribute ("@ElectronicReporting:NumChars"), SysOperationDisplayOrderAttribute ("3")]
    public ERExpressionInt parmNumChars(ERExpressionInt _numChars = numChars)
    {
        numChars = _numChars;
        return numChars;
    }
    [DataMemberAttribute, SysOperationLabelAttribute ("@ElectronicReporting:StartNum"), SysOperationDisplayOrderAttribute ("2")]
    public ERExpressionInt parmStartNum(ERExpressionInt _startNum = startNum)
    {
        startNum = _startNum;
        return startNum;
    }
    public str toString()
    {
        return ERExpressionStringPresenter::namedFunctionToStr(this);
    }
}

Suggested guidance

The following guidance is intended to help you design your custom ER functions:

• Reuse the names of Microsoft Excel functions whenever you can, so that ER formulas remain Excel-like. In this way, you will keep ER formulas intelligible for end users.
• ER doesn't support list types for primitive data types. Therefore, we have decided to use a data container list that has a single Value item in it.
• Release a new function's list extension as a new application hotfix. ER designers will refer to the hotfix number in ER configurations that use that new custom function. Whenever a configuration of this type is imported into a new instance, ER will evaluate whether the required hotfix has been installed, to maintain compliance between the ER configuration and the version that configuration is imported into.

Additional resources

Electronic reporting (ER) overview

Formula designer in Electronic reporting (ER)