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annotate m-toolbox/html_help/help/ug/repo_retrieve_content.html @ 29:54f14716c721 database-connection-manager

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Update Java code
author Daniele Nicolodi <nicolodi@science.unitn.it>
date Mon, 05 Dec 2011 16:20:06 +0100
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1 <p>
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2 Objects can be retrieved from the repository either by specifying an object ID or a collection ID. The LTPDA
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3 Toolbox provides class construtors to retrieve objects. In additon, to retrieve a collection of objects, the <tt>collection</tt> class
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4 can be used.
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5 </p>
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6 <br>
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7 <h2>The retrieval process</h2>
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8 <p>
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9 When an object is retrieved, the following steps are taken:
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10 <ol>
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11 <li>The object type for the requested ID is retrieved from the <tt>objmeta</tt> table</li>
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12 <li>A call is made to the appropriate class constructor</li>
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13 <li>The class constructor retrieves the XML string from the objs table</li>
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14 <li>The XML string is then converted into an XML Xdoc object</li>
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15 <li>The Xdoc object is then parsed to recreate the desired object</li>
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16 </ol>
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17 </p>
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18
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19 <br>
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20 <h2>Retrieving objects</h2>
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21
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22 <p>
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23 To retrieve an object, you must know its object ID, or the ID of the collection that contains that object. If you don't know the
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24 class of the object, you can use the <tt>collection</tt> class as a container, as follows:
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25 <div class="fragment"><pre>
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26 >> a = collection(plist('hostname', 'localhost', 'database', 'ltpda_test', 'id', 1))
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27
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28 ** Connection status:
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29 LWB: Disconnected from localhost/ltpda_test as hewitson
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30 ---- collection 1 ----
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31 name: none
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32 num objs: 1
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33 01: ao | New Block/tsdataNdata=[10x1], fs=1, nsecs=10, t0=1970-01-01 00:00:00.000
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34 description:
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35 UUID: 9ec7a613-9442-4451-9b40-af18f4afea00
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36 ----------------------
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37 </pre></div>
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38 </p>
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39 <p>
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40 If you already know the class of the object (for example, <tt>ao</tt>), you can directly call the class constructor method:
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41 <div class="fragment"><pre>
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42 <span class="comment">% Define the hostname and database</span>
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43 hostname = <span class="string">'localhost'</span>;
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44 database = <span class="string">'ltpda_test'</span>;
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45
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46 <span class="comment">% Retrieve the object</span>
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47 q = ao(plist(<span class="string">'hostname'</span>, hostname, <span class="string">'database'</span>, dbname, <span class="string">'ID'</span>, 12));
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48 </pre></div>
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49 </p>
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50
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51 <br>
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52 <p>
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53 Multiple objects can be retrieved simultaneously by giving a list of object IDs. For example
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54 <div class="fragment"><pre>
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55 >> a = ao(plist('hostname', 'localhost', 'database', 'ltpda_test', 'id', [1 2 3]))
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56 </pre></div>
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57 </p>
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58 <br>
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59 <h2>Retrieving object collections</h2>
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60 <p>
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61 Collections of objects can be retrieved by specifying the collection ID. The following script retrieves a collection:
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62 <div class="fragment"><pre>
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63 >> a = collection(plist('hostname', 'localhost', 'database', 'ltpda_test', 'cid', 1))
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64 </pre></div>
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65 The output is a <tt>collection</tt> object containing the objects retrieved.
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66 </p>
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67
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68 <h2>Retrieving binary objects</h2>
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69 <p>The retrieval process may be speeded up by taking advantage of the fact that the objects are stored in the databases also in binary form.
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70 This can be achieved by using the parameter 'binary', that will build the object from the corresponding binary representation, if
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71 stored in the database.
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72 <div class="fragment"><pre>
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73 <span class="comment">% Retrieve the collection</span>
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74 q = ao(plist(<span class="string">'hostname'</span>, hostname, <span class="string">'database'</span>, dbname, <span class="string">'ID'</span>, 12, <span class="string">'binary'</span>, <span class="string">'yes'</span>));
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75 </pre></div>
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76 If the binary representation is not in the database, the object will be built from the xml one.
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77 </p>