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require 'sqlite3'include SQLite3class Db    private     :exec    attr_reader :structure    def initialize(db_name, hash_structure={})        # this hash has the tables names as key and an array composed of arries of string as value,        # each string array being of form %w( varname type )        # e.g.: @structure = {         #           "table1" => [ ["id", "integer primary key"], %w(name varchar), %w(date datetime) ]        #           "table2" => [ %w(place varstring), %w(personnumber int) ]        #       }        @structure = hash_structure        if not File.exist?(db_name)            @db = Database.new(db_name)            @structure.each { |table, value|                command = "create table #{table}("                value.each { |column|                    command += " #{column[0]} #{column[1]}"                    command += (value.index(column) + 1 == value.length ? ')' : ',' )                }                @db.execute(command)            }        else            @db = Database.new(db_name)            # populate @structure with the tables of the db            tables = @db.execute('select * from sqlite_master')            tables.each { |table|                types = table[4][/\(.*\)/].delete("(").delete(")").split(',')                @structure[table[1]] = types.each_index { |type| types[type] = types[type].split(' ') }            }        end    end    def add_table(name, array_structure)        return false if exist?(name)        command = "create table '#{name}'("        array_structure.each { |column|            command += " #{column[0]} #{column[1]}"            command += (array_structure.index(column) + 1 == array_structure.length ? ')' : ',' )        }        exec(command) ? @structure[name] = array_structure : (return false)        return true    end    def add(table, ar_fields=nil, *values)        str_value = ""        values.each { |value| str_value += "'#{value}'," }        str_value.chop!        str_fields = "("        ar_fields.each { |field| str_fields += "#{field}," }        str_fields = str_fields.chop + ")"        str_fields = nil if not ar_fields         return true if exist?(table) and exec("insert into '#{table}'#{str_fields} values(#{str_value})")        return false    end    def find(table, condition=nil, *columns)        return false if not exist?(table)        if columns.length != 0            columns.each { |column| return false if not exist?(table, column) }        end        columns = (columns == [] ? '*' : columns.each_index { |i| columns[i] += ' ' }.to_s)        result = exec("select #{columns} from '#{table}' #{condition}")        return (result != [] ? result : false)    end    def erase(table, condition)        return false if not exist?(table)        return exec("delete from #{table} #{condition}")    end    def update(table, column, new_value, condition=nil)        return false if not exist?(table, column)        new_value = %Q-"#{new_value}"- if new_value.class == String        return exec("update '#{table}' set #{column} = #{new_value} #{condition}")    end    def exist?(table, column=nil)        if @structure.has_key?(table)            return true if not column             @structure[table].length.times { |i|                return true if @structure[table][i][0] == column            }        end        return false    end    def exec(string)        begin            result = @db.execute(string)            puts string.inspect # debug            return result        rescue SQLException            puts string            puts "error: " + $!            return false        end    endend