textOnlySqlTypes top-level constant
Types the driver has no dedicated model for, which dbconvert returns as
their canonical text.
They are not unknown and they are not lost: logicalTypeFor in the driver
falls back to varchar, so the value arrives as a String. Whoever
generates code from a schema should read them and never write them, since
writing needs the CLR type itself.
Implementation
const Set<String> textOnlySqlTypes = <String>{
'hierarchyid',
'geometry',
'geography',
'sql_variant',
};