From: steve <zyzygy@...>
Date: 2009-11-10T11:15:10+09:00
Subject: Re: errors when using sqlite3's query and prepare methods

Robert Citek wrote:
> Hello all,
> 
> I'm trying to prepare a sql statement to send to sqlite3 via ruby and
> am getting errors when using the query and prepare methods.  Here's my
> code:
> 
> #!/usr/bin/env ruby
> require 'sqlite3'
> db = SQLite3::Database.new( "test.db" )
> 
> # create the database
> sql = <<-eof
>   CREATE TABLE foobar (foo text, bar int);
>   INSERT INTO "foobar" VALUES('hello',1);
>   INSERT INTO "foobar" VALUES('world',2)
>   eof
> db.execute_batch(sql)
> 
> # querying the database via execute works
> db.execute( "select * from foobar" ) do |row|
>   puts row.join("\t") ;
> end
> 
> # querying the database via query method does not work
> db.query( "select * from foobar" ) do |row|
>   puts row.join("\t") ;
> end
> 
> # querying the database via a prepare does not work
> db.prepare( "select * from foobar" ) do |stmnt|
>   stmnt.execute do |row|
>     puts row.join("\t") ;
>   end
> end
> 
> Below is the output from running the execute, query, and prepare methods in irb:
> 
> irb(main):036:0> # querying the database via execute works
> irb(main):037:0* db.execute( "select * from foobar" ) do |row|
> irb(main):038:1*   puts row.join("\t") ;
> irb(main):039:1* end
> hello	1
> world	2
> => nil
> irb(main):040:0>
> irb(main):041:0* # querying the database via query method does not work
> irb(main):042:0* db.query( "select * from foobar" ) do |row|
> irb(main):043:1*   puts row.join("\t") ;
> irb(main):044:1* end
> NoMethodError: undefined method `join' for #<SQLite3::ResultSet:0xb7c6bae4>
> 	from (irb):43
> 	from /usr/lib/ruby/1.8/sqlite3/database.rb:278:in `query'
> 	from (irb):42
> irb(main):045:0>
> irb(main):046:0* # querying the database via a prepare does not work
> irb(main):047:0* db.prepare( "select * from foobar" ) do |stmnt|
> irb(main):048:1*   stmnt.execute do |row|
> irb(main):049:2*     puts row.join("\t") ;
> irb(main):050:2*   end
> irb(main):051:1> end
> NoMethodError: undefined method `join' for #<SQLite3::ResultSet:0xb7c3c190>
> 	from (irb):49
> 	from /usr/lib/ruby/1.8/sqlite3/statement.rb:166:in `execute'
> 	from (irb):48
> 	from /usr/lib/ruby/1.8/sqlite3/database.rb:187:in `prepare'
> 	from (irb):47
> 
> $ ruby -v
> ruby 1.8.6 (2007-09-24 patchlevel 111) [i486-linux]
> 
> $ irb -v
> irb 0.9.5(05/04/13)
> 
> I've been looking at the docs[1] and the FAQ[2].  Clearly I'm
> overlooking something, but what?
> 
> Thanks in advance to any pointers.
> 
> [1] http://sqlite-ruby.rubyforge.org/sqlite3/
> [2] http://sqlite-ruby.rubyforge.org/sqlite3/faq.html
> 
> Regards,
> - Robert
> 

Hello Robert.

Look carefully at the error messages.  In the case that works you are 
applying a join.  If you look at the type of the object it is 
SQLite3::ResultSet::ArrayWithTypesAndFields. This object responds to join.

irb(main):011:0> db.execute( "select * from foobar" ) do |row|
irb(main):012:1*   puts row.join("\t") ;
irb(main):013:1*   puts row.class
irb(main):014:1> end
hello   1
SQLite3::ResultSet::ArrayWithTypesAndFields
world   2
SQLite3::ResultSet::ArrayWithTypesAndFields
=> nil

In the failing attempts the message indicates that the object returned 
is SQLite3::ResultSet, which does not respond to join.

Doc indicates that SQLite3::ResultSet responds to each... so

irb(main):019:0> db.query( "select * from foobar" ).each do |row|
irb(main):020:1*   puts row.join("\t") ;
irb(main):021:1*   puts row.class
irb(main):022:1> end
hello   1
SQLite3::ResultSet::ArrayWithTypesAndFields
world   2
SQLite3::ResultSet::ArrayWithTypesAndFields
=> nil
irb(main):023:0>

This may be a an omission in the documentation of teh gem as there 
appears to be no reference for the 
SQLite3::ResultSet::ArrayWithTypesAndFields object.