C# Nhibernate | PL/SQL Oracle - different length of string when it contains diacritical marks

Question

I have example string, which I'm trying to put as value in VARCHAR(255) column (in oracle database) using nhibernate ISession object.

abssssssssssssssssssssssssd RRRRRRRRRRRRRRRAAAAAAAAAAAAAAAąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąassssssssssssssssss ansssssssssssssssssssssssssssssssssssssssssssssssssssssss ssssssssssssssssssssss

From application level I check string.Length and it is as expected (255). Additionaly I'm also doing following query to database:

            const string lengthCheckSql = @"SELECT LENGTH(:valueToCheck) as charCount FROM DUAL";
            var result = _session.CreateSQLQuery(lengthCheckSql)
                .AddScalar("charCount", NHibernateUtil.Int32)
                .SetString("valueToCheck", valueToCheck)
                .UniqueResult<int>();

Which also returns expected value (255).

By the end, when I call Save from ISession object, then I'm getting exception from database that ,,valueToCheck" has bigger length as allowed in database; ,,(current: 352, allowed: 255)"

When I change ,ą' to ,a' then everything works fine.

I'm trying to find where is a problem - is Nhibernate by default converts some chars to different unicode than my database allow to use ?

Answer 1

The string is 255 characters long. It is also 352 bytes long:

SELECT LENGTH(
         'abssssssssssssssssssssssssd RRRRRRRRRRRRRRRAAAAAAAAAAAAAAAąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąassssssssssssssssss ansssssssssssssssssssssssssssssssssssssssssssssssssssssss ssssssssssssssssssssss' 
       ) AS charCount,
       LENGTHB(
         'abssssssssssssssssssssssssd RRRRRRRRRRRRRRRAAAAAAAAAAAAAAAąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąassssssssssssssssss ansssssssssssssssssssssssssssssssssssssssssssssssssssssss ssssssssssssssssssssss'
       ) AS byteCount
FROM   DUAL

Outputs:

CHARCOUNT	BYTECOUNT
255	352

If you do:

CREATE TABLE table_name (value VARCHAR2(255 /*BYTE*/));

INSERT INTO table_name (value) VALUES ('abssssssssssssssssssssssssd RRRRRRRRRRRRRRRAAAAAAAAAAAAAAAąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąassssssssssssssssss ansssssssssssssssssssssssssssssssssssssssssssssssssssssss ssssssssssssssssssssss');

Then you get the error:

ORA-12899: value too large for column "SCHEMA_NAME"."TABLE_NAME"."VALUE" (actual: 352, maximum: 255)

You can look at the data dictionary for the table:

SELECT table_name, column_name, data_type, data_length, char_length, char_used
FROM   user_tab_columns
WHERE  table_name = 'TABLE_NAME'
AND    column_name = 'VALUE';

Which outputs:

TABLE_NAME	COLUMN_NAME	DATA_TYPE	DATA_LENGTH	CHAR_LENGTH	CHAR_USED
TABLE_NAME	VALUE	VARCHAR2	255	255	B

It can store up to 255 characters but it can only store 255 bytes so any multi-byte characters are going to reduce the maximum usable length.

---

If you change the column to 255 characters (rather than 255 bytes):

ALTER TABLE table_name MODIFY value VARCHAR2(255 CHAR);

Then:

INSERT INTO table_name (value) VALUES ('abssssssssssssssssssssssssd RRRRRRRRRRRRRRRAAAAAAAAAAAAAAAąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąąassssssssssssssssss ansssssssssssssssssssssssssssssssssssssssssssssssssssssss ssssssssssssssssssssss');

Works.

The data dictionary now contains:

TABLE_NAME	COLUMN_NAME	DATA_TYPE	DATA_LENGTH	CHAR_LENGTH	CHAR_USED
TABLE_NAME	VALUE	VARCHAR2	1020	255	C

It can also store 255 characters but it can now store 1020 bytes (i.e. 255 characters with up to 4 bytes per character).

fiddle