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User friendlier errors from utils.mysql.connect
author Daniele Nicolodi <nicolodi@science.unitn.it>
date Mon, 05 Dec 2011 18:04:03 +0100
parents f0afece42f48
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<p>
  Parameters can be grouped together into parameter lists (<tt>plist</tt>).
</p>	

<ul>
  <li><a href="plist_create.html#direct">Creating parameter lists directly</a></li>
  <li><a href="plist_create.html#append">Appending parameters to a parameter list</a></li>
  <li><a href="plist_create.html#find">Finding parameters in a parameter list</a></li>
  <li><a href="plist_create.html#remove">Removing parameters from a parameter list</a></li>
  <li><a href="plist_create.html#set">Setting parameters in a parameter list</a></li>
  <li><a href="plist_create.html#combine">Combining multiple parameter lists</a></li>
</ul>


<!-- From parameters -->
<hr>
<h3><a name="params"></a>Creating parameter lists from parameters.</h3>


<!-- Direct -->
<hr>
<h3><a name="direct"></a>Creating parameter lists directly.</h3>
<p> 
You can also create parameter lists directly using the following constructor format:</p>
<div class="fragment"><pre>
  pl = plist(<span class="string">'a'</span>, 1, <span class="string">'b'</span>, <span class="string">'hello'</span>)
</pre></div>
will result in the following output
<div class="fragment"><pre>
    ----------- plist 01 -----------
    n params: 2
    ---- param 1 ----
    key:  A
    val:  1
    -----------------
    ---- param 2 ----
    key:  B
    val:  'hello'
    -----------------
    description: 
    UUID:        9cc7d1f1-6ca3-477b-a6cc-2629d52579e6
--------------------------------
</pre></div>

<!-- Append -->
<hr>
<h3><a name="append"></a>Appending parameters to a parameter list.</h3>
<p>
Additional parameters can be appended to an existing parameter list using the <tt>append</tt> 
method:</p>
<div class="fragment"><pre>
  pl  = append(pl, <span class="string">'c'</span>, 3)  <span class="comment">% append a third parameter</span>
</pre></div>
will result in the following output
<div class="fragment"><pre>
    ----------- plist 01 -----------
    n params: 3
    ---- param 1 ----
    key: A
    val: 1 
    -----------------
    ---- param 2 ----
    key: B
    val: 'hello'
    -----------------
    ---- param 3 ----
    key: C
    val: 3 
    -----------------
    --------------------------------
</pre></div>


<!-- Access -->
<hr>
<h3><a name="find"></a>Finding parameters in a parameter list.</h3>
<p>
  Accessing the contents of a <tt>plist</tt> can be achieved in two ways:
</p>
<div class="fragment"><pre>
  p1  = pl.params(1);   <span class="comment">% get the first parameter</span>
  val = find(pl, <span class="string">'b'</span>);  <span class="comment">% get the second parameter</span>
</pre></div>
<p>
  If the parameter name ('key') is known, then you can use the <tt>find</tt> method to 
  directly retrieve the value of that parameter.
</p>

<!-- Remove -->
<hr>
<h3><a name="remove"></a>Removing parameters from a parameter list.</h3>
<p>
  You can also remove parameters from a parameter list:
  <div class="fragment"><pre>
    pl = remove(pl, 2) <span class="comment">% Remove the 2nd parameter in the list</span>
    pl = remove(pl, <span class="string">'a'</span>) <span class="comment">% Remove the parameter with the key 'a'</span>
  </pre></div>
</p>

<!-- Set -->
<hr>
<h3><a name="set"></a>Setting parameters in a parameter list.</h3>
<p>
  You can also set parameters contained in a parameter list:
  <div class="fragment"><pre>
    pl = plist(<span class="string">'a'</span>, 1, <span class="string">'b'</span>, <span class="string">'hello'</span>)
    pl = pset(pl, <span class="string">'a'</span>, 5, <span class="string">'b'</span>, <span class="string">'ola'</span>);  <span class="comment">% Change the values of the parameter with the keys 'a' and 'b'</span>
  </pre></div>
</p>


<!-- Combine -->
<hr>
<h3><a name="combine"></a>Combining multiple parameter lists.</h3>

<p>
  Parameter lists can be combined:
  <div class="fragment"><pre>
    pl = combine(pl1, pl2)
  </pre></div>
  If <tt>pl1</tt> and <tt>pl2</tt> contain a parameter with the same key name, the output <tt>plist</tt> contains a parameter with that name but with the value from the first parameter list input.
</p>