About expressions in derived properties

An expression can be used in a derived IDO property to convey the value of the property when the property is used.

Expressions used in derived properties must be SQL expressions that are used to define the value of the derived property. The expression is included when data is selected from the table and may be any expression that can be evaluated in SQL SELECT statements.

The expression can be used to perform calculations, sub-queries, or calls to SQL functions.

When used as part of an expression, property names are case-sensitive.

To allow for variable values to be used, you can parameterize elements of an expression can be parameterized. For example, suppose you have a derived property that uses this expression:

Price * Quantity

You can now create a property class that contains this expression, and inherit it from the derived property. This effectively makes it reusable; that is, you can create multiple derived properties that inherit from this property class and inherit this expression.

Not only are expressions inheritable, but they can also be parameterized. So, you could change the expression to something like this:

{0} * {1}

To do this, use the “{n}” format to specify placeholders for the parameter values.

This means that, from a derived property, you can specify the arguments “Price, Quantity”, and these arguments are substituted into the parameters when the property is used.

Note: Parameters are zero-based indexes, and the arguments are presented as a comma-delimited list. So, in this example, “Price” corresponds to parameter {0} and “Quantity” corresponds to parameter {1}.