Re: how to save a bytea value into a file?

Hello Laurenz Albe

Thank you for your replying.
In Fact, I'm doing a porting project from Oracle 10g to PostgreSQL 9.0.4

There is a procedure in Oracle 10g to write a blob value into a file using:
...
V_TOTAL_SIZE := DBMS_LOB.GETLENGTH(V_BLOB);
    V_FILE_TYPE := UTL_FILE.FOPEN('RADIUS_DIR', V_FILE_NAME, V_OPEN_MODE,
V_BUFFER_SIZE);
    WHILE V_OFFSET < V_TOTAL_SIZE LOOP
        IF V_TOTAL_SIZE < V_OFFSET + V_AMOUNT THEN
            V_AMOUNT := V_TOTAL_SIZE - V_OFFSET + 1;
        END IF;
        DBMS_LOB.READ(V_BLOB, V_AMOUNT, V_OFFSET, V_BUFFER);
        UTL_FILE.PUT_RAW(V_FILE_TYPE, V_BUFFER, TRUE);
        V_OFFSET := V_OFFSET + V_AMOUNT;
        DBMS_OUTPUT.PUT_LINE ('Offset : ' || V_OFFSET);
    END LOOP;
    UTL_FILE.FCLOSE(V_FILE_TYPE);
...
I know PostgreSQL doesn't support procedure, so I want to porting it into a
function use LANGUAGE plpgsql.
So I must find some APIs supported by plpgsql to write a bytea value into a
file (e.g. write into a file in RedHat)

★ Are there any APIs like "UTL_FILE.FOPEN... DBMS_LOB.READ...
UTL_FILE.PUT_RAW..." of Oracle dealing with writing binary objects into a
file in PostgreSQL? If there isn't anyone, Maybe I should think about other
language(e.g. Perl, Java) to realize it.

Waiting for your reply^^~

Best Regards
Fanlijing
2011-10-10
-----Original Message-----
From: Albe Laurenz [mailto:laurenz.albe@wien.gv.at]
Sent: Monday, October 10, 2011 3:28 PM
To: fanlijing *EXTERN*; pgsql-admin@postgresql.org;
pgsql-general@postgresql.org
Subject: RE: [GENERAL] how to save a bytea value into a file?

fanlijing wrote:
> When I want to save a bytea value into a file, what should I do？
> Is there any function dealing with that in PostgreSQL? (like lo_export()
to
> deal with the large-object) (# I didn't find any....)

If you want to save it in a file on the server, you can use
the COPY statement.

If you want to create that file on the client machine, you'll
have to select and fetch it like any other value, then open
a file and write the contents into it.

If the bytea is large, you could select parts of it (with the
substring() function) and thus do it in pieces.

For some APIs, you could also use COPY TO STDOUT.

Details depend on the API and programming language you are using.

Yours,
Laurenz Albe