root/main/trunk/greenstone2/perllib/gssql.pm @ 32574

Revision 32574, 24.8 KB (checked in by ak19, 4 months ago)

Instead of my our own caching of SQL prepare statements within the gssql object (gssql.pm), there is the handy dbh->prepare_cached() command that encapsulates away the same behaviour for us (if used correctly). Tested this worked. Testing was of regular full rebuilds, incr delete, non-incr delete, reindex upon rename.

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1###########################################################################
2#
3# gssql.pm -- DBI for SQL related utility functions used by
4# GreenstoneSQLPlugout and hereafter by GreenstoneSQLPlugin too.
5# A component of the Greenstone digital library software
6# from the New Zealand Digital Library Project at the
7# University of Waikato, New Zealand.
8#
9# Copyright (C) 1999 New Zealand Digital Library Project
10#
11# This program is free software; you can redistribute it and/or modify
12# it under the terms of the GNU General Public License as published by
13# the Free Software Foundation; either version 2 of the License, or
14# (at your option) any later version.
15#
16# This program is distributed in the hope that it will be useful,
17# but WITHOUT ANY WARRANTY; without even the implied warranty of
18# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
19# GNU General Public License for more details.
20#
21# You should have received a copy of the GNU General Public License
22# along with this program; if not, write to the Free Software
23# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
24#
25###########################################################################
26
27package gssql;
28
29use strict;
30no strict 'refs';
31no strict 'subs';
32
33use DBI; # the central package for this module used by GreenstoneSQL Plugout and Plugin
34
35# Need params_map keys:
36# - collection_name
37# - db_encoding (db content encoding) - MySQL can set this at server, db, table levels. For MySQL
38# we set the enc during connect at server level. Not sure whether other DB's support it at the
39# same levels.
40
41# For connection to MySQL, need:
42#  - db_driver, db_client_user, db_client_pwd, db_host, (db_port not used at present)
43# So these will be parameterised, but in a hashmap, for just the connect method.
44
45# Parameterise (one or more methods may use them):
46# - db_name (which is the GS3 sitename)
47
48# TODO: add infrastructure for db_port, AutoCommit etc
49# For port, see https://stackoverflow.com/questions/2248665/perl-script-to-connect-to-mysql-server-port-3307
50
51sub new
52
53    my $class = shift(@_);
54   
55    my ($params_map) = @_;
56   
57    # library_url: to be specified on the cmdline if not using a GS-included web server
58    # the GSDL_LIBRARY_URL env var is useful when running cmdline buildcol.pl in the linux package manager versions of GS3
59   
60    # https://stackoverflow.com/questions/7083453/copying-a-hashref-in-perl
61    # Making a shallow copy works, and can handle unknown params:
62    #my $self = $params_map;
63
64    # but being explicit for class params needed for MySQL:
65    my $self = {
66    'collection_name' => $params_map->{'collection_name'},
67    'verbosity' => $params_map->{'verbosity'} || 1
68    };
69
70    # The db_encoding option is presently not passed in to this constructor as parameter.
71    # Placed here to indicate it's sort of optional.
72    # Since docxml are all in utf8, the contents of the GS SQL database should be too,
73    # So making utf8 the hidden default at present.
74    $self->{'db_encoding'} = $params_map->{'db_encoding'} || "utf8";
75   
76    $self = bless($self, $class);   
77
78    $self->{'tablename_prefix'} = $self->sanitize_name($params_map->{'collection_name'});
79   
80    return $self;
81}
82
83
84#################################
85
86# Database access related functions
87# http://g2pc1.bu.edu/~qzpeng/manual/MySQL%20Commands.htm
88# https://www.guru99.com/insert-into.html
89
90# TODO Q: What on cancelling a build: delete table? But what if it was a rebuild and the rebuild is cancelled (not the original build)?
91# Do we create a copy of the orig database as backup, then start populating current db, and if cancelled, delete current db and RENAME backup table to current?
92# https://stackoverflow.com/questions/3280006/duplicating-a-mysql-table-indexes-and-data
93# BUT what if the table is HUGE? (Think of a collection with millions of docs.) Huge overhead in copying?
94# The alternative is we just quit on cancel, but then: cancel could leave the table in a partial committed state, with no way of rolling back.
95# Unless they do a full rebuild, which will recreate the table from scratch?
96# SOLUTION-> rollback transaction on error, see https://www.effectiveperlprogramming.com/2010/07/set-custom-dbi-error-handlers/
97# But then should set AutoCommit to off on connection, and remember to commit every time
98
99#################
100# Database functions that use the perl DBI module (with the DBD driver module for mysql)
101#################
102
103################### BASIC DB OPERATIONS ##################
104
105# THE NEW DB FUNCTIONS
106# NOTE: FULLTEXT is a reserved keyword in (My)SQL. So we can't name a table or any of its columns "fulltext".
107# https://dev.mysql.com/doc/refman/5.5/en/keywords.html
108
109# TODO: Consider AutoCommit status (and Autocommit off allowing commit or rollback for GS coll build cancel) later
110
111# TODO: where should the defaults for these params be, here or in GS-SQLPlugin/Plugout?
112sub connect_to_db {
113    my $self= shift (@_);
114    my ($params_map) = @_;
115    # For proper utf8 support in MySQL, encoding should be 'utf8mb4' as 'utf8' is insufficient
116    my $db_enc = "utf8mb4" if $self->{'db_encoding'} eq "utf8";
117
118    # these are the params for connecting to MySQL
119    my $db_driver = $params_map->{'db_driver'} || "mysql";
120    my $db_user = $params_map->{'db_client_user'} || "root";
121    my $db_pwd = $params_map->{'db_client_pwd'}; # even if undef, we'll see a sensible error message
122                                           # when connect fails
123    my $db_host = $params_map->{'db_host'} || "127.0.0.1";
124    # localhost doesn't work for us, but 127.0.0.1 works
125    # https://metacpan.org/pod/DBD::mysql
126    # "The hostname, if not specified or specified as '' or 'localhost', will default to a MySQL server
127    # running on the local machine using the default for the UNIX socket. To connect to a MySQL server
128    # on the local machine via TCP, you must specify the loopback IP address (127.0.0.1) as the host."
129    #my $connect_str = "dbi:$db_driver:database=$db_name;host=$db_host";
130    my $connect_str = "dbi:$db_driver:host=$db_host"; # don't provide db - allows checking the db exists later when loading the db
131
132    if($self->{'verbosity'}) {
133    print STDERR "Away to make connection to $db_driver database with:\n";
134    print STDERR " - hostname $db_host; username: $db_user";
135    print STDERR "; and the provided password" if $db_pwd;
136    print STDERR "\nAssuming the mysql server has been started with: --character_set_server=utf8mb4\n" if $db_driver eq "mysql";
137    }
138   
139    my $dbh = DBI->connect("$connect_str", $db_user, $db_pwd,
140               {
141                   ShowErrorStatement => 1, # more informative as DBI will append failed SQL stmt to error message
142                   PrintError => 1, # on by default, but being explicit
143                   RaiseError => 0, # off by default, but being explicit
144                   AutoCommit => 1, # on by default, but being explicit
145                   mysql_enable_utf8mb4 => 1 # tells MySQL to use UTF-8 for communication and tells DBD::mysql to decode the data, see https://stackoverflow.com/questions/46727362/perl-mysql-utf8mb4-issue-possible-bug
146               });
147
148    if(!$dbh) {
149    # NOTE, despite handle dbh being undefined, error code will be in DBI->err (note caps)
150    return 0;   
151    }
152
153    # set encoding https://metacpan.org/pod/DBD::mysql
154    # https://dev.mysql.com/doc/refman/5.7/en/charset.html
155    # https://dev.mysql.com/doc/refman/5.7/en/charset-conversion.html
156    # Setting the encoding at db server level: $dbh->do("set NAMES '" . $db_enc . "'");
157    # HOWEVER:
158    # It turned out insufficient setting the encoding to utf8, as that only supports utf8 chars that
159    # need up to 3 bytes. We may need up to 4 bytes per utf8 character, e.g. chars with macron,
160    # and for that, we need the encoding to be set to utf8mb4.
161    # To set up a MySQL db to use utf8mb4 requires configuration on the server side too.
162    # https://stackoverflow.com/questions/10957238/incorrect-string-value-when-trying-to-insert-utf-8-into-mysql-via-jdbc
163    # https://stackoverflow.com/questions/46727362/perl-mysql-utf8mb4-issue-possible-bug
164    # To set up the db for utf8mb4, therefore,
165    # the MySQL server needs to be configured for that char encoding by running the server as:
166    # mysql-5.7.23-linux-glibc2.12-x86_64/bin>./mysqld_safe --datadir=/Scratch/ak19/mysql/data --character_set_server=utf8mb4
167    # AND when connecting to the server, we can can either set mysql_enable_utf8mb4 => 1
168    # as a connection option
169    # OR we need to do both "set NAMES utf8mb4" AND "$dbh->{mysql_enable_utf8mb4} = 1;" after connecting
170    #
171    # Search results for DBI Set Names imply the "SET NAMES '<enc>'" command is mysql specific too,
172    # so setting the mysql specific option during connection above as "mysql_enable_utf8mb4 => 1"
173    # is no more objectionable. It has the advantage of cutting out the 2 extra lines of doing
174    # set NAMES '<enc>' and $dbh->{mysql_enable_utf8mb4} = 1 here.
175    # These lines may be preferred if more db_driver options are to be supported in future:
176    # then a separate method called set_db_encoding($enc) can work out what db_driver we're using
177    # and if mysql and enc=utfy, then it can do the following whereas it will issue other do stmts
178    # for other db_drivers, see https://www.perlmonks.org/?node_id=259456:
179   
180    #my $stmt = "set NAMES '" . $db_enc . "'";
181    #$dbh->do($stmt) || warn("Unable to set charset encoding at db server level to: " . $db_enc . "\n"); # tells MySQL to use UTF-8 for communication
182    #$dbh->{mysql_enable_utf8mb4} = 1; # tells DBD::mysql to decode the data
183   
184    # if we're here, then connection succeeded, store handle
185    $self->{'db_handle'} = $dbh;
186    return 1;
187}
188
189# Load the designated database, i.e. 'use <dbname>;'.
190# If the database doesn't yet exist, creates it and loads it.
191# (Don't create the collection's tables yet, though)
192# At the end it will have loaded the requested database (in MySQL: "use <db>;") on success.
193# As usual, returns success or failure value that can be evaluated in a boolean context.
194sub use_db {
195    my $self= shift (@_);
196    my ($db_name) = @_;
197    my $dbh = $self->{'db_handle'};
198    $db_name = $self->sanitize_name($db_name);
199   
200    print STDERR "Attempting to use database $db_name\n" if($self->{'verbosity'});
201   
202    # perl DBI switch database: https://www.perlmonks.org/?node_id=995434
203    # do() returns undef on error.
204    # connection succeeded, try to load our database. If that didn't work, attempt to create db
205    my $success = $dbh->do("use $db_name");
206   
207    if(!$success && $dbh->err == 1049) { # "Unknown database" error has code 1049 (mysql only?) meaning db doesn't exist yet
208
209    print STDERR "Database $db_name didn't exist, creating it along with the tables for the current collection...\n" if($self->{'verbosity'});
210   
211    # attempt to create the db and its tables
212    $self->create_db($db_name) || return 0;
213
214    print STDERR "   Created database $db_name\n" if($self->{'verbosity'} > 1);
215   
216    # once more attempt to use db, now that it exists
217    $dbh->do("use $db_name") || return 0;
218    #$dbh->do("use $db_name") or die "Error (code" . $dbh->err ."): " . $dbh->errstr . "\n";
219
220    $success = 1;
221    }
222    elsif($success) { # database existed and loaded successfully, but
223    # before proceeding check that the current collection's tables exist
224
225    print STDERR "@@@ DATABASE $db_name EXISTED\n" if($self->{'verbosity'} > 2);
226    }
227   
228    return $success; # could still return 0, if database failed to load with an error code != 1049
229}
230
231
232# We should already have done "use <database>;" if this gets called.
233# Just load this collection's metatable
234sub ensure_meta_table_exists {
235    my $self = shift (@_);
236   
237    my $tablename = $self->get_metadata_table_name();
238    if(!$self->table_exists($tablename)) {
239    #print STDERR "   Creating metadata table $tablename\n" if($self->{'verbosity'} > 1);
240    $self->create_metadata_table() || return 0;
241    } else {
242    print STDERR "@@@ Meta table exists\n" if($self->{'verbosity'} > 2);
243    }
244    return 1;
245}
246
247# We should already have done "use <database>;" if this gets called.
248# Just load this collection's metatable
249sub ensure_fulltxt_table_exists {
250    my $self = shift (@_);
251   
252    my $tablename = $self->get_fulltext_table_name();   
253    if(!$self->table_exists($tablename)) {
254    #print STDERR "   Creating fulltxt table $tablename\n" if($self->{'verbosity'} > 1);
255    $self->create_fulltext_table() || return 0;
256    } else {
257    print STDERR "@@@ Fulltxt table exists\n" if($self->{'verbosity'} > 2);
258    }
259    return 1;
260}
261
262# disconnect from db - https://metacpan.org/pod/DBI#disconnect
263# TODO: make sure to have committed or rolled back before disconnect
264# and that you've call finish() on statement handles if any fetch remnants remain
265sub disconnect_from_db {
266    my $self= shift (@_);   
267    my $dbh = $self->{'db_handle'};
268
269    # make sure any active stmt handles are finished
270    # NO: "When all the data has been fetched from a SELECT statement, the driver will automatically call finish for you. So you should not call it explicitly except when you know that you've not fetched all the data from a statement handle and the handle won't be destroyed soon."
271   
272    print STDERR "Disconnecting from database\n" if($self->{'verbosity'} > 1);
273   
274    my $rc = $dbh->disconnect or warn $dbh->errstr; # The handle is of little use after disconnecting. Possibly PrintError already prints a warning and this duplicates it?
275    return $rc;
276}
277
278sub create_db {
279    my $self= shift (@_);
280    my ($db_name) = @_;
281    my $dbh = $self->{'db_handle'};
282    $db_name = $self->sanitize_name($db_name);
283   
284    # https://stackoverflow.com/questions/5025768/how-can-i-create-a-mysql-database-from-a-perl-script
285    return $dbh->do("create database $db_name"); # do() will return undef on fail, https://metacpan.org/pod/DBI#do
286}
287
288
289sub create_metadata_table {
290    my $self= shift (@_);
291    my $dbh = $self->{'db_handle'};
292   
293    my $table_name = $self->get_metadata_table_name();
294    print STDERR "   Creating table $table_name\n" if($self->{'verbosity'} > 1);
295   
296    # If using an auto incremented primary key:
297    my $stmt = "CREATE TABLE $table_name (id INT NOT NULL AUTO_INCREMENT, did VARCHAR(63) NOT NULL, sid VARCHAR(63) NOT NULL, metaname VARCHAR(127) NOT NULL, metavalue VARCHAR(1023) NOT NULL, PRIMARY KEY(id));";
298    return $dbh->do($stmt);
299}
300
301# TODO: Investigate: https://dev.mysql.com/doc/search/?d=10&p=1&q=FULLTEXT
302# 12.9.1 Natural Language Full-Text Searches
303# to see whether we have to index the 'fulltxt' column of the 'fulltext' tables
304# or let user edit this file, or add it as another option
305sub create_fulltext_table {
306    my $self= shift (@_);
307    my $dbh = $self->{'db_handle'};
308   
309    my $table_name = $self->get_fulltext_table_name();
310    print STDERR "   Creating table $table_name\n" if($self->{'verbosity'} > 1);
311   
312    # If using an auto incremented primary key:
313    my $stmt = "CREATE TABLE $table_name (id INT NOT NULL AUTO_INCREMENT, did VARCHAR(63) NOT NULL, sid VARCHAR(63) NOT NULL, fulltxt LONGTEXT, PRIMARY KEY(id));";
314    return $dbh->do($stmt);
315
316}
317
318# "IF EXISTS is used to prevent an error from occurring if the database does not exist. ... DROP DATABASE returns the number of tables that were removed. The DROP DATABASE statement removes from the given database directory those files and directories that MySQL itself may create during normal operation.Jun 20, 2012"
319# MySQL 8.0 Reference Manual :: 13.1.22 DROP DATABASE Syntax
320# https://dev.mysql.com/doc/en/drop-database.html
321sub delete_collection_tables {
322    my $self= shift (@_);
323    my $dbh = $self->{'db_handle'};
324   
325    # drop table <tablename>
326    my $table = $self->get_metadata_table_name();
327    if($self->table_exists($table)) {
328    $dbh->do("drop table $table") || warn("@@@ Couldn't delete $table");
329    }
330    $table = $self->get_fulltext_table_name();
331    if($self->table_exists($table)) {
332    $dbh->do("drop table $table") || warn("@@@ Couldn't delete $table");
333    }
334}
335
336# Don't call this: it will delete the meta and full text tables for ALL collections in $db_name (localsite by default)!
337# This method is just here for debugging (for testing creating a database when there is none)
338sub _delete_database {
339    my $self= shift (@_);
340    my ($db_name) = @_;
341    my $dbh = $self->{'db_handle'};
342    $db_name = $self->sanitize_name($db_name);
343   
344    print STDERR "!!! Deleting database $db_name\n" if($self->{'verbosity'});
345   
346    # "drop database dbname"
347    $dbh->do("drop database $db_name") || return 0;
348
349    return 1;
350}
351
352
353########################### DB STATEMENTS ###########################
354
355# USEFUL: https://metacpan.org/pod/DBI
356# "Many methods have an optional \%attr parameter which can be used to pass information to the driver implementing the method. Except where specifically documented, the \%attr parameter can only be used to pass driver specific hints. In general, you can ignore \%attr parameters or pass it as undef."
357
358# More efficient to use prepare() to prepare an SQL statement once and then execute() it many times
359# (binding different values to placeholders) than running do() which will prepare each time and
360# execute each time. Also, do() is not useful with SQL select statements as it doesn't fetch rows.
361# Can prepare and cache prepared statements or retrieve prepared statements if cached in one step:
362# https://metacpan.org/pod/release/TIMB/DBI-1.634_50/DBI.pm#prepare_cached
363
364# https://www.guru99.com/insert-into.html
365# and https://dev.mysql.com/doc/refman/8.0/en/example-auto-increment.html
366#     for inserting multiple rows at once
367# https://www.perlmonks.org/bare/?node_id=316183
368# https://metacpan.org/pod/DBI#do
369# https://www.quora.com/What-is-the-difference-between-prepare-and-do-statements-in-Perl-while-we-make-a-connection-to-the-database-for-executing-the-query
370# https://docstore.mik.ua/orelly/linux/dbi/ch05_05.htm
371
372# https://metacpan.org/pod/DBI#performance
373# 'The q{...} style quoting used in this example avoids clashing with quotes that may be used in the SQL statement. Use the double-quote like qq{...} operator if you want to interpolate variables into the string. See "Quote and Quote-like Operators" in perlop for more details.'
374#
375# This method uses lazy loading to prepare the SQL insert stmt once for a table and store it,
376# then execute the (stored) statement each time it's needed for that table.
377sub insert_row_into_metadata_table {
378    my $self = shift (@_);
379    my ($doc_oid, $section_name, $meta_name, $escaped_meta_value, $debug_only, $debug_out) = @_;
380   
381    my $dbh = $self->{'db_handle'};
382   
383    my $tablename = $self->get_metadata_table_name();
384    my $sth = $dbh->prepare_cached(qq{INSERT INTO $tablename (did, sid, metaname, metavalue) VALUES (?, ?, ?, ?)}) || warn("Could not prepare insert statement for metadata table\n");
385
386    # Now we're ready to execute the command, unless we're only debugging
387   
388    if($debug_only) {
389    # just print the statement we were going to execute
390   
391    print $debug_out $sth->{'Statement'} . "($doc_oid, $section_name, $meta_name, $escaped_meta_value)\n";
392    } else {
393    $sth->execute($doc_oid, $section_name, $meta_name, $escaped_meta_value)
394        || warn ("Unable to write metadata row to db:\n\tOID $doc_oid, section $section_name,\n\tmeta name: $meta_name, val: $escaped_meta_value");
395    # Execution failure will print out info anyway: since db connection sets PrintError
396    }
397}
398
399# As above. Likewise uses lazy loading to prepare the SQL insert stmt once for a table and store it,
400# then execute the (stored) statement each time it's needed for that table.
401sub insert_row_into_fulltxt_table {
402    my $self = shift (@_);
403    #my ($did, $sid, $fulltext) = @_;
404    my ($doc_oid, $section_name, $section_textref, $debug_only, $debug_out) = @_;
405   
406    my $dbh = $self->{'db_handle'};
407   
408    my $tablename = $self->get_fulltext_table_name();
409    my $sth = $dbh->prepare_cached(qq{INSERT INTO $tablename (did, sid, fulltxt) VALUES (?, ?, ?)}) || warn("Could not prepare insert statement for fulltxt table\n");
410   
411    # Now we're ready to execute the command, unless we're only debugging
412
413    if($debug_only) {
414    # just print the statement we were going to execute, minus the fulltxt value
415    my $txt_repr = $$section_textref ? "<TXT>" : "NULL";
416    print $debug_out $sth->{'Statement'} . "($doc_oid, $section_name, $txt_repr)\n";
417    } else {
418    $sth->execute($doc_oid, $section_name, $$section_textref)
419        || warn ("Unable to write fulltxt row to db for row:\n\tOID $doc_oid, section $section_name");
420    }
421}
422
423
424## The 2 select statements used by GreenstoneSQLPlugin
425
426#https://metacpan.org/pod/release/TIMB/DBI-1.634_50/DBI.pm#selectall_arrayref
427# Returns the statement handle that prepared and executed
428# a "SELECT * FROM <COLL>_metadata WHERE did = $oid" SQL statement.
429# Caller can call fetchrow_array() on returned statement handle, $sth
430# Have to use prepare() and execute() instead of do() since do() does
431# not allow for fetching result set thereafter:
432# do(): "This method  is typically most useful for non-SELECT statements that either cannot be prepared in advance (due to a limitation of the driver) or do not need to be executed repeatedly. It should not be used for SELECT statements because it does not return a statement handle (so you can't fetch any data)." https://metacpan.org/pod/release/TIMB/DBI-1.634_50/DBI.pm#do
433sub select_from_metatable_matching_docid {
434    my $self= shift (@_);
435    my ($oid) = @_;
436   
437    my $dbh = $self->{'db_handle'};
438    my $meta_table = $self->get_metadata_table_name();
439   
440    my $sth = $dbh->prepare_cached(qq{SELECT * FROM $meta_table WHERE did = ?});
441    $sth->execute( $oid ); # will print msg on fail
442   
443    return $sth; # caller can call fetchrow_array() on returned statement handle, sth
444}
445
446
447#https://metacpan.org/pod/release/TIMB/DBI-1.634_50/DBI.pm#selectall_arrayref
448# Returns the statement handle that prepared and executed
449# a "SELECT * FROM <COLL>_metadata WHERE did = $oid" SQL statement.
450# Caller can call fetchrow_array() on returned statement handle, $sth
451sub select_from_texttable_matching_docid {
452    my $self= shift (@_);
453    my ($oid) = @_;
454   
455    my $dbh = $self->{'db_handle'};
456    my $fulltxt_table = $self->get_fulltext_table_name();
457   
458    my $sth = $dbh->prepare_cached(qq{SELECT * FROM $fulltxt_table WHERE did = ?});
459    $sth->execute( $oid ); # will print msg on fail
460   
461    return $sth; # caller can call fetchrow_array() on returned statement handle, sth
462}
463
464# delete all records in metatable with specified docid
465# https://www.tutorialspoint.com/mysql/mysql-delete-query.htm
466# DELETE FROM table_name [WHERE Clause]
467# see example under 'do' at https://metacpan.org/pod/release/TIMB/DBI-1.634_50/DBI.pm
468sub delete_recs_from_metatable_with_docid {
469    my $self= shift (@_);
470    my ($oid) = @_;
471   
472    my $dbh = $self->{'db_handle'};
473
474    my $tablename = $self->get_metadata_table_name();
475    my $sth = $dbh->prepare_cached(qq{DELETE FROM $tablename WHERE did = ?});
476    $sth->execute( $oid ) or warn $dbh->errstr; # dbh set to print errors even without doing warn()
477}
478
479# delete all records in metatable with specified docid
480sub delete_recs_from_texttable_with_docid {
481    my $self= shift (@_);
482    my ($oid) = @_;
483   
484    my $dbh = $self->{'db_handle'};
485
486    my $tablename = $self->get_fulltext_table_name();
487    my $sth = $dbh->prepare_cached(qq{DELETE FROM $tablename WHERE did = ?});
488    $sth->execute( $oid ) or warn $dbh->errstr; # dbh set to print errors even without doing warn()
489}
490
491# Can call this after connection succeeded to get the database handle, dbh,
492# if any specific DB operation (SQL statement, create/delete)
493# needs to be executed that is not already provided as a method of this class.
494sub get_db_handle {
495    my $self= shift (@_);
496    return $self->{'db_handle'};
497}
498
499################ HELPER METHODS ##############
500
501# More basic helper methods
502sub get_metadata_table_name {
503    my $self= shift (@_);
504    my $table_name = $self->{'tablename_prefix'} . "_metadata";
505    return $table_name;
506}
507
508# FULLTEXT is a reserved keyword in (My)SQL. https://dev.mysql.com/doc/refman/5.5/en/keywords.html
509# So we can't name a table or any of its columns "fulltext". We use "fulltxt" instead.
510sub get_fulltext_table_name {
511    my $self= shift (@_);
512    my $table_name = $self->{'tablename_prefix'} . "_fulltxt";
513    return $table_name;
514}
515
516# Attempt to make sure the name parameter (for db or table name) is acceptable syntax
517# for the db in question, e.g. for mysql. For example, (My)SQL doesn't like tables or
518# databases with '-' (hyphens) in their names
519sub sanitize_name {
520    my $self= shift (@_);
521    my ($name) = @_;
522    $name =~ s/-/_/g;
523    return $name;
524}
525
526
527# I can get my version of table_exists to work, but it's not so ideal
528# Interesting that MySQL has non-standard command to CREATE TABLE IF NOT EXISTS and DROP TABLE IF EXISTS,
529# see https://www.perlmonks.org/bare/?node=DBI%20Recipes
530#    The page further has a table_exists function that could work with proper comparison
531# TODO Q: Couldn't get the first solution at https://www.perlmonks.org/bare/?node_id=500050 to work though
532sub table_exists {
533    my $self = shift (@_);
534    my $dbh = $self->{'db_handle'};
535    my ($table_name) = @_;
536
537    my @table_list = $dbh->tables;
538    #my $tables_str = @table_list[0];
539    foreach my $table (@table_list) {
540    return 1 if ($table =~ m/$table_name/);
541    }
542    return 0;
543}
544
5451;
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