When adding Unmapped fields(ones we do not intend to link up with any datasource field on the entity itself) to a data entity in Dynamics 365. You may receive the below compile error:

The property ‘ComputedFieldMethod’ must be set with the name of a valid data entity method if ‘IsComputedField’ is set to ‘Yes’.

Solution:

This is because AX is expecting a computed method for it within the entity, when we do not intend to create that we need to Set the Is Computed Field property under Mics group to No