You can use ClassFromString in OCL when you need to turn a class name held as a string back into a model type so that you can query that type's metadata; this is for modelers working with types rather than instances.

Convert between a type and its string representation

When you work meta—that is, when an expression examines the structure of your model—you may need to move between a type and text.

Direction	Operator	Result	Example use
Type to string	AsString	The type represented as a string	Store or compare a class name as text.
String to type	ClassFromString	An OclType that you can use to inspect the represented class	Read a tagged value from the represented class.

Use ClassFromString on a string that represents a model type. The returned value is an OclType, not an instance of that class. This distinction matters: use it to access type-level information such as tagged values, rather than attributes on an object instance.

For the operator syntax and reference example, see Documentation:OCLOperators classfromstring.

Filter subclasses by a class tagged value

A common use is to start with the string values returned by allSubClasses, convert each string to its class type, and then inspect a tagged value on that class.

For example, suppose ComponentSpecification has several subclasses. Mark the subclasses that must be excluded with the tagged value TypeSort set to SKIPTHIS. Use this OCL expression:

ComponentSpecification.allSubClasses->select(x | x.ClassFromString.TaggedValue('TypeSort') <> 'SKIPTHIS')

The expression works as follows:

1. ComponentSpecification.allSubClasses supplies the subclasses as strings.
2. select evaluates each subclass string as x.
3. x.ClassFromString converts that string to the corresponding class type.
4. TaggedValue('TypeSort') reads the TypeSort tagged value from that class.
5. The comparison retains every subclass whose value is not SKIPTHIS.

The result is a collection of subclass strings. It is not a collection of class instances. If you need to perform a further type-level lookup for a selected value, apply ClassFromString to that value again.

Keep the string and tag values consistent

ClassFromString depends on the string identifying a model type. In the filtering example, the tag name and exclusion value must also match the values configured on the classes:

• Use the same tagged-value name in the model and expression, for example TypeSort.
• Use the same exclusion value, for example SKIPTHIS.
• Apply ClassFromString before TaggedValue; a string does not expose class metadata until it has been converted to an OclType.

See also

• Documentation:OCLOperators classfromstring
• Documentation:Learn OCL
• Documentation:Class