These features would be nice to have.
The current implementation cannot be extended to support all of these
features in read/write mode, because with a shutdown compact, the whole file
is rewritten.
1) Blank lines are fine anywhere in read-only mode.
2) We need a property to allow fixed-width fields. It is easy to implement,
only the Writer needs changes. If you want to also implement fixe-width
fields without separators (leaving out the pipe in your example), it would
need a bit more work, both in Reader and Writer.
3) Whole line Comments can be supported in read only mode. We need to allow
the comment character as a SET TABLE .. SOURCE property and skip the lines
beginning with this character in the Reader.
Also, the header line can be used to calculate the max field-widths and
these can be checked against the size parameters for CHAR(N) and VARCHAR(N)
fields, enforcing the equivalent of the system property
sql.enforce_strict_size.
It would be better to introduce these features together with the ability to
allow end of line characters in (quoted) character fields. This feature has
been frequently requested by users and a patch was supplied for this against
1.7.1, but due to lack of time, it has not been ported to 1.7.2. Dimitri,
the patch author, is still around and may be able to offer some help.
Fred
----- Original Message -----
From: "Blaine Simpson" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: 01 June 2004 16:36
Subject: [Hsqldb-developers] features for consideration for text files
These features all have to do with Hsqldb reading in externally created
text-files.
I hand-edit text files written by other programs, and I create some
entirely manually.
I keep these files under change control, so it's very useful to be able
to keep
tracking information, historical information, and notes in the text file
itself. I
currently run a perl pre-processor on my text files to remove my edits
and blank
lines before importing them to Hsqldb. It would be nice if this could
be handled
by Hsqldb directly.
I understand that when Hsqldb rewrites the text file, these comments,
etc. will
be wiped out, but it is still extremely useful to me to be able to use
these features
in my import source files.
Does anybody else think that any of these features would be useful to
the general
Hsqldb public, or the opposite?
(1) Safe use of blank lines. It "looks like" blank lines are ok, since
the doc says
that when db synces the file it replaces an ignored first line with a
blank line. If
blank lines are safe anywhere within an externally created text file,
I'd like to
know about it.
(2) Trimming. I've been using shell scripts for many years that use DB
flat files
like
value one is long |val2 |val3 |val4
val1b short |val2b long |val3b and |valu4b
(where the delimiter is "|"). The reason for the extra white space is
so that the
files line up whether the file is viewed with an ASCII editor, catted,
mored, etc.
Otherwise it is a mess like this:
value one is long|val2|val3|val4
val1b short|val2blong|val3b and|val4b
The reason I prefer the first is that you can easily tell which value is for
which field. You can't tell with the latter unless you count
delimiters. This can
be implemented by Java trimming each field value. (For backwards
compatibility
may want to have a setting to toggle the behavior, but 99% of the time
you don't
want values with leading or trailing whitespace in the database).
(3) Comments. It would be nice if the user could specify a comment
character
so that you can have comment lines anywhere in the file.
val1|val2|val3|val4
# Commenting out following 2 for this revision because Sam is on
vacation
# val11|val12|val13|val14
#val21|val22|val23|val24
val31|val32|val33|val34
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