Ruby：哈希陣列的列名和值對來自YAML

Question

我有這個YAML條目;

table: 
    - name: table_a 
select: 
    - id: source.id 
    - code: source.code 
    - name: source.name 
    - is_active: TRUE 

我需要將它讀入HASH數組並構造一個像這樣的SELECT SQL語句;

SELECT 
    source.id as id, 
    source.code as code, 
    source.name as name, 
    TRUE as is_active 
FROM table_a 

我很努力地訪問HASH | key，value |動態配對。

我使用了這段代碼;

yml = YAML.load_file("file.yml") 
yml.each_pair { |key, value| puts "#{key} = #{value}"} 

但是當我使用yml['select'].each_pair我得到「未定義的方法`each_pair」錯誤。

Answer 1

基於YAML的，這裏是如何解析它：

asdf = YAML.load('table: 
    - name: table_a 
select: 
    - id: source.id 
    - code: source.code 
    - name: source.name 
    - is_active: TRUE 
    - created_at: Time.now() 
    - updated_at: Time.now()') 
=> {"table"=>[{"name"=>"table_a"}], 
"select"=> 
    [{"id"=>"source.id"}, 
    {"code"=>"source.code"}, 
    {"name"=>"source.name"}, 
    {"is_active"=>true}, 
    {"created_at"=>"Time.now()"}, 
    {"updated_at"=>"Time.now()"}]} 

你YAML也沒有創造一個容易解析的數據結構，它是讓你赴湯蹈火訪問元素：

asdf['table'][0]['name'] 
=> "table_a" 

asdf['select'][4]['created_at'] 
=> "Time.now()" 

相反，它應該是這樣的：

table: 
    name: table_a 
select: 
    id: source.id 
    code: source.code 
    name: source.name 
    is_active: TRUE 
    created_at: Time.now() 
    updated_at: Time.now() 

其中，解析後，將創建的哈希哈希看起來像：

{ 
    "table"=>{ 
    "name" => "table_a" 
    }, 
    "select" => 
    { 
    "id"   => "source.id", 
    "code"  => "source.code", 
    "name"  => "source.name", 
    "is_active" => true, 
    "created_at" => "Time.now()", 
    "updated_at" => "Time.now()" 
    } 
} 

這可以讓你輕鬆，也很直觀，訪問內容：

asdf['table'] 
=> {"name"=>"table_a"} 
asdf['select']['created_at'] 
=> "Time.now()" 

YAML不會把字符串"Time.now()"成一個Ruby Time.now方法調用，所以編碼字符串進入YAML數據將無濟於事。

相反，解析之後，使用方法：

time_now = Time.now 
select = asdf['select'] 
select['created_at'] = time_now 
select['updated_at'] = time_now 

您可以通過-操作前傳入YAML，然後解析它更新您的"Time.now()"字符串：

yaml_string = ' 
table: 
    name: table_a 
select: 
    id: source.id 
    code: source.code 
    name: source.name 
    is_active: TRUE 
    created_at: Time.now() 
    updated_at: Time.now() 
' 
yaml_string.gsub!('Time.now()', Time.now.to_s) 

導致：

table: 
    name: table_a 
select: 
    id: source.id 
    code: source.code 
    name: source.name 
    is_active: TRUE 
    created_at: 2012-12-28 10:09:21 -0700 
    updated_at: 2012-12-28 10:09:21 -0700 

解析它現在返回：

=> {"table"=>{"name"=>"table_a"}, 
"select"=> 
    {"id"=>"source.id", 
    "code"=>"source.code", 
    "name"=>"source.name", 
    "is_active"=>true, 
    "created_at"=>2012-12-28 10:09:21 -0700, 
    "updated_at"=>2012-12-28 10:09:21 -0700}} 

而且YAML可以做到與時間價值的東西，因爲它認識它：

[14] pry(main)> asdf['select']['created_at'] 
=> 2012-12-28 10:09:21 -0700 
[15] pry(main)> asdf['select']['created_at'].class 
=> Time 

此外，而不是寫自己的SQL，我強烈建議使用ORM，像Sequel或DataMapper。我贊同Sequel，但無論如何，優勢在於您不必編寫查詢，ORM就是這樣做的。你告訴它要訪問哪些數據庫和表，並找出模式和關係。如果你使用Rails，ActiveRecord是一個很好的ORM，它與Rails結合在一起。它可以單獨使用，但如果您不使用Rails，我會先推薦其他兩個。