Applying Constraints
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In almost every data model, there are values that are not supported for a particular field. In an “M” model, you add constraints to specify the range of valid values for each field in your extent.
Adding Constraints
Consider a Contact model that contains a Hometowns extent. One requirement for this extent could specify that the State field should accept the two-letter state abbreviations rather than the full state name. The following code example shows how to add this constraint to the State field.
Hometowns :
{(
{
Id : Integer64 => AutoNumber;
City : Text;
State : Text where value.Count == 2;
}
)*} where identity Id;
There are many different kinds of constraints that can ensure the validity of data added to your models. For more information, see Constraints ("M" Programming Guide).