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POActiverecord, select on string compare
 

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  1. POActiverecord, select on string compare
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    <p>I have a table called Basic , start_time is one field with type :VARCHAR(5), which actually stores a 5 bytes time data: byte 0 and 1 map to the year , month and day, and byte 2 to 4 map to the hour, min and second. So, it could possible bytes 2 ,3 ,4 are all 0. And I want to do following query :</p> <pre><code>Basic.find (:all , :conditions =&gt; "start_time &gt; ? AND end_time &lt; ?" , start_time , end_time) </code></pre> <p>Here are the questions:</p> <p>Suppose in VARCHAR(5) format ,the start time is [214, 222,0 ,0, 0] (Jun, 24th, 2009) and the end time is [214, 223, 0, 0, 0] (Jun , 25, 2009).</p> <p>As activerecord maps VARCHAR(5) to String , so in above query the start_time and end_time should also be String. What is the correct way to convert above VARCHAR(5) format time to the String?</p> <p>I did it this way, but fails to get correct result:</p> <pre><code>tmp = [214, 222,0 ,0 ,0].map {|t| t.to_s(16)} ; start_time = tmp.to_s </code></pre> <p>And i was using sqlite3 adapter for activerecord. </p> <p>Thanks for your help.</p> <hr> <p>I have found where the problem is: "\000" is not allowed to be contained in the start_time when do follwing query:</p> <pre><code>Basic.find (:all , :conditions =&gt; "start_time &gt; ? AND end_time &lt; ?" , start_time , end_time) </code></pre> <p>So, I need to do two steps:</p> <ol> <li><p>[214, 222,0 ,0, 0] - > [214,222]</p></li> <li><p>[214,222] -> "\326\336"</p></li> </ol> <p>The 1st steps can be done using:</p> <pre><code>a = [214,222,0,0,0] while a.last ==0 do a.pop end </code></pre> <p>The 2nd steps can be done using:</p> <pre><code>a = [214,222] a.pack("c" * a.size) </code></pre> <p>However, I still can not do query when start_time = [214, 222,0 ,23, 0] , because the corresponding string contains "\000" in the middle. fortunately, It would not be a big problem in our appication , as we never query in hours level, that means last two number will always be 0.</p>
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    1. USpierrotlefou
    1. USpierrotlefou
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    1. COWhy aren't you using a date type? If you're using SQLite, I assume it's not a legacy setup...
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      1. USSarah Mei
    2. COThe legacy database saved the time in its original format - MJD for year and BCD codin for hour , min and second. It works well when using sqlite3 API and so far I have not seen any compelling reason to save it in the date type.
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      1. USpierrotlefou
 

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