Delphi dbExpress and Interbase: UTF8 migration steps and risks?

Question

Currently, our database uses Win1252 as the only character encoding. We will have to support Unicode in the database tables soon, which means we have to perform this migrati

Answer 1

Both Database Workbench and IBExpert can do the data migration for you.

I'll get back to you on the other questions when I'm at the Entwickler Tage.

--jeroen

Answer 2

Problem: UDF (user defined functions) with string parameters can break because of sizes limits.

Symptom:

Dynamic SQL Error.
SQL error code = -204.
Data type unknown.
Implementation limit exceeded.
COLUMN DSQL internal.

for this UDF:

DECLARE EXTERNAL FUNCTION STRLEN
    CSTRING(32767)
    RETURNS INTEGER BY VALUE
    ENTRY_POINT 'IB_UDF_strlen' MODULE_NAME 'ib_udf';

Solution: fix UDF parameters in the declaration.

Answer 3

Problem: dbExpress uses WideString as data type internally, so all existing .AsString calls for reading / setting field and parameter will no longer work

Symptom: special characters will not be stored / read correctly

Solution: replace all occurences of .AsString with .AsWideString but be careful to not change where the AsString method is not called on a field or parameter.

Answer 4

Problem: UPDATE on a empty string field no longer finds a record. If a UTF8 character field is empty, the DataSetProvider generates a wrong SELECT for the update action.

Symptom: Message 'record not found or edited by another user'

Solution: upgrade to Delphi 2010 Update 4 or use the workaround described in QC

Answer 5

Problem: dbExpress needs TStringField objects for WIN1252 fields. For UTF8 database fields, dbExpress needs TWideStringField objects.

Symptom: error message 'expected: WideString found: string'

Solution: replace all occurences of TStringField with TWideStringField. This requires that all form files (dfm) are text, not binary. The modified forms and datamodules will not be backwards compatible.

Answer 6

Problem: persistent string fields require a Size property which is the logical size of the field multiplied by four (see also: Is it possible to tweak TStringField to work like TWideStringField in Delphi?)

Symptom: Access violations

Solution: delete the persistent field and add it again to update the Size property. (side effect: the DisplayWidth will also increase size, leading to problems with UI)