Key length for an Index in Entity Engine

[Hans Holmlund]

I want to create an index on a TEXT column. When doing this the 
key-length to use for the index must be specified, otherwise I get the 
following error message:
"BLOB/TEXT column 'ABSOLUTE_PATH' used in key specification without a 
key length".

How do I specify the key-length in the entitymodel definition?
Thanks,

Hans Holmlund