Ruby on Rails 入门之：(24) Ruby 中数据持久化、数据库操作
1. 数据库操作概述
Ruby中的数据库接口成为DBI（Database Inte易做图ce），它是对底层的数据库驱动进行的抽象，形成的不同数据库之间的统一的接口。
2. 数据库操作的基本链接
在操作mysql数据库的时候需要引用外部文件“mysql”，在程序的开始部分添加：
[ruby]
require ""mysql;
require ""mysql;
下面给出一个基本的链接查询程序：
[ruby]
#encoding:utf-8
require "mysql"
dbh = Mysql.real_connect("localhost","root","","infosys",3306);
sql = "select * from students"
res = dbh.query(sql);
while row=res.fetch_row
puts row[0].to_s;
puts row[1].to_s;
puts row[2].to_s;
puts row[3].to_s;
end
#encoding:utf-8
require "mysql"
dbh = Mysql.real_connect("localhost","root","","infosys",3306);
sql = "select * from students"
res = dbh.query(sql);
while row=res.fetch_row
puts row[0].to_s;
puts row[1].to_s;
puts row[2].to_s;
puts row[3].to_s;
end
几乎所有的数据库链接查询都是这样操作，主机名，用户名，密码，数据库，端口，然后是查询语句，最后在查询结果集里遍历查询结果。
上面的输出结果为：
[ruby]
watkins@watkins:~/temp/workspace/ruby$ ruby db.rb
1
weisong
male
1881*******
watkins@watkins:~/temp/workspace/ruby$
watkins@watkins:~/temp/workspace/ruby$ ruby db.rb
1
weisong
male
1881*******
watkins@watkins:~/temp/workspace/ruby$
3. 使用MySQL模块查询结果集
在使用query方法执行完查询语句以后，如果该SQL 语句有返回值，那么返回的是一个Mysql::Result类的实例。
可以使用fetch_row来取得结果集中的一行。
[ruby]
#encoding:utf-8
require "mysql"
dbh = Mysql.real_connect("localhost","root","","infosys",3306);
sql = "select * from students"
res = dbh.query(sql);
while row=res.fetch_row
puts row[0].to_s;
puts row[1].to_s;
puts row[2].to_s;
puts row[3].to_s;
end
#encoding:utf-8
require "mysql"
dbh = Mysql.real_connect("localhost","root","","infosys",3306);
sql = "select * from students"
res = dbh.query(sql);
while row=res.fetch_row
puts row[0].to_s;
puts row[1].to_s;
puts row[2].to_s;
puts row[3].to_s;
end
也可以直接使用结果集自身的迭代来进行遍历结果集中的数据：
[ruby]
#encoding:utf-8
require "mysql"
dbh = Mysql.real_connect("localhost","root","","infosys",3306);
sql = "select * from students"
res = dbh.query(sql);
#while row=res.fetch_row
# puts row[0].to_s;
# puts row[1].to_s;
# puts row[2].to_s;
# puts row[3].to_s;
#end
puts "***********************************";
res.each do |row|
puts "#{row[0]} \t #{row[1]} \t #{row[2]}";
end
#encoding:utf-8
require "mysql"
dbh = Mysql.real_connect("localhost","root","","infosys",3306);
sql = "select * from students"
res = dbh.query(sql);
#while row=res.fetch_row
# puts row[0].to_s;
# puts row[1].to_s;
# puts row[2].to_s;
# puts row[3].to_s;
#end
puts "***********************************";
res.each do |row|
puts "#{row[0]} \t #{row[1]} \t #{row[2]}";
end
4. 向数据写入特殊字符
在应用程序中，难免有时候会向数据库中写入特殊字符，例如 单引号，双引号，分号等等，向数据库中保存这些符号需要使用escape_string方法来处理这些特殊字符。
[ruby]
#encoding:utf-8
require "mysql"
dbh = Mysql.real_connect("localhost","root","","infosys",3306);
#sql = "select * from students"
msg = "this is a legal text 4\"3' ";
puts msg;
msg = dbh.escape_string("this is a legal text 4\"3'' ");
sql = "insert into students values(3,'ccc','male','156896532','#{msg}')";
res = dbh.query(sql);
puts dbh.affected_rows;
dbh.close;
#while row=res.fetch_row
# puts row[0].to_s;
# puts row[1].to_s;
# puts row[2].to_s;
# puts row[3].to_s;
#end
#puts "***********************************";
#res.each do |row|
# puts "#{row[0]} \t #{row[1]} \t #{row[2]}";
#end
#encoding:utf-8
require "mysql"
dbh = Mysql.real_connect("localhost","root","","infosys",3306);
#sql = "select * from students"
msg = "this is a legal text 4\"3' ";
puts msg;
msg = dbh.escape_string("this is a legal text 4\"3'' ");
sql = "insert into students values(3,'ccc','male','156896532','#{msg}')";
res = dbh.query(sql);
puts dbh.affected_rows;
dbh.close;
#while row=res.fetch_row
# puts row[0].to_s;
# puts row[1].to_s;
# puts row[2].to_s;
# puts row[3].to_s;
#end
#puts "***********************************";
#res.each do |row|
# puts "#{row[0]} \t #{row[1]} \t #{row[2]}";
#end
5. 查询结果集元数据
可以使用num_rows方法 ， num_fields方法获取查询结果集中的行数，列数。
还可以使用fetch_field获取字符，获得这个字段的各种属性。
[ruby]
#encoding:utf-8
require "mysql"
dbh = Mysql.real_connect("localhost","root","","infosys",3306);
sql = "select * from students"
#msg = "this is a legal text 4\"3' ";
#puts msg;
#msg = dbh.escape_string("this is a legal text 4\"3'' ");
#sql = "insert into students values(3,'ccc','male','156896532','#{msg}')";
res = dbh.query(sql);
puts dbh.affected_rows;
dbh.close;
#while row=res.fetch_row
# puts row[0].to_s;
# puts row[1].to_s;
# puts row[2].to_s;
#
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