Wednesday, November 28, 2018

Orafce - simple thing that can help

I merged small patch to master branch of Orafce. This shows a wide PostgreSQL possibilities and can decrease a work necessary for migration from Oracle to Postgres.

One small/big differences between Oracle and any other databases is meaning of empty string. There are lot of situation, when Oracle use empty string as NULL, and NULL as empty string. I don't know any other database, that does it.

Orafce has native type (not domain type) varchar2 and nvarchar2. Then it is possible to define own operators. I implemented || concat operator as null safe for these types. So now it is possible to write:
postgres=# select null || 'xxx'::varchar2 || null;
│ ?column? │
│ xxx      │
(1 row)

When you port some application from Oracle to Postgres, then is good to disallow empty strings in Postgres. One possible solution is using generic C trigger function replace_empty_string(). This trigger function can check any text type field in stored rows and can replace empty strings by NULLs. Sure, you should to fix any check like colname = '' or colname <> '' in your application, and you should to use just only colname IS [NOT] NULL. Then the code will be same on Oracle and PostgreSQL too, and you can use automatic translation by ora2pg.

Orafce || (n)varchar2 operator automatically convert empty string to NULL.


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