2 Say, you have several gigabytes of data in a file. The whole object doesn't need to be serialized at once. You can read and write the value partially using [[svn:foundation/databoard/trunk/org.simantics.databoard/src/org/simantics/databoard/accessor/|Accessor]] interface. The actual container can be a file, memory byte[]/ByteBuffer or a Java Object. The content is structured as tree using Databoard's type system. All but referable records are supported (=no recursion in accessors).
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4 '''[../javadoc/org/simantics/databoard/accessor.html|org.simantics.databoard.accessor] interfaces'''.
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5 {| style="background-color: #e9e9e9; border: 1px solid #aaaaaa; "
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8 |- style="background-color: #f9f9f9; " |
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9 | [../javadoc/org/simantics/databoard/accessor/Accessor.html|Accessor]
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10 | Base class for all data Accessors
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11 |- style="background-color: #f9f9f9; " |
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12 | [../javadoc/org/simantics/databoard/accessor/RecordAccessor.html|RecordAccessor]
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14 |- style="background-color: #f9f9f9; " |
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15 | [../javadoc/org/simantics/databoard/accessor/ArrayAccessor.html|ArrayAccessor]
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16 | Array - an ordered sequence of elements of one value.
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17 |- style="background-color: #f9f9f9; " |
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18 | [../javadoc/org/simantics/databoard/accessor/MapAccessor.html|MapAccessor]
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19 | Map - an ''ordered'' map of keys to values.
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20 |- style="background-color: #f9f9f9; " |
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21 | [../javadoc/org/simantics/databoard/accessor/UnionAccessor.html|UnionAccessor]
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23 |- style="background-color: #f9f9f9; " |
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24 | [../javadoc/org/simantics/databoard/accessor/BooleanAccessor.html|BooleanAccessor],[../javadoc/org/simantics/databoard/accessor/IntAccessor.html|IntAccessor],[../javadoc/org/simantics/databoard/accessor/LongAccessor.html|LongAccessor],[../javadoc/org/simantics/databoard/accessor/FloatAccessor.html|FloatAccessor],[../javadoc/org/simantics/databoard/accessor/DoubleAccessor.html|DoubleAccessor]
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25 | Primitive and numeric Accessors
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26 |- style="background-color: #f9f9f9; " |
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27 | [../javadoc/org/simantics/databoard/accessor/StringAccessor.html|StringAccessor]
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29 |- style="background-color: #f9f9f9; " |
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30 | [../javadoc/org/simantics/databoard/accessor/OptionalAccessor.html|OptionalAccessor]
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32 |- style="background-color: #f9f9f9; " |
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33 | [../javadoc/org/simantics/databoard/accessor/VariantAccessor.html|VariantAccessor]
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37 [../javadoc/org/simantics/databoard/Accessors.html|Accessors] and [../javadoc/org/simantics/databoard/Files.html|Files] are facade classes that contains utilities for instantiating and handling Accessors.
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39 <code>[../javadoc/org/simantics/databoard/accessor/binary/index.html|Binary Accessor]</code> is an access to a value in binary format (<tt>byte[]</tt> or <tt>ByteBuffer</tt>).
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41 '''Example:''' Binary accessor
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43 Datatype type = Datatypes.getDatatype( Rectangle2D.Double.class );
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44 Binding binding = Bindings.getBinding( Rectangle2D.Double.class );
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45 Serializer s = Binding.getSerializer( binding );
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47 // Serialize rectangle
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48 Rectangle2D rect = new Rectangle2D.Double(0,0, 10, 10);
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49 byte[] data = s.serialize(rect);
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51 // Open accessor to byte data and modify first field in the byte data
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52 RecordAccessor ra = Accessors.getAccessor(data, type);
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53 ra.setFieldValue(0, Bindings.DOUBLE, 5.0);
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55 // Deserialize values from the byte data back to the rectangle object
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56 s.deserialize(data, rect);
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57 System.out.println(rect.getX());
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60 '''Example:''' File accessor, create
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62 RecordType type = Datatypes.getDatatype( Rectangle2D.Double.class );
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63 // Create a new file and initialize it with rectangle type, and open file accessor
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64 FileRecordAccessor fa = Accessors.createFile( file, type );
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66 // Write the first field (x)
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67 fa.setFieldValue(0, Bindings.DOUBLE, 5.0);
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71 '''Example:''' File accessor, open
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73 // Open an accessor to an existing binary file
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74 FileVariantAccessor fa = Accessors.openAccessor(file);
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75 RecordAccessor ra = fa.getContentAccessor();
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77 // Read the first field (x)
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78 Double x = (Double) ra.getFieldValue(0, Bindings.DOUBLE);
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82 '''Example:''' Java Accessor
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84 Binding binding = Bindings.getBinding(Rectangle2D.Double.class);
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85 Rectangle2D rect = new Rectangle2D.Double(0,0, 10, 10);
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87 // Open accessor to rectangle
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88 RecordAccessor ra = Accessors.getAccessor(binding, rect);
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90 // Set rectangle's first field (x) to 5.0
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91 ra.setFieldValue(0, Bindings.DOUBLE, 5.0);
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92 System.out.println( rect.getX() );
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96 ==Accessor Reference==
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97 Accessors can be opened to a sub-nodes with AccessorReference or by calling getAccessor. AccessorReference is a string of instances, either accessor type specific of LabelReferences.
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99 ChildReference ref = ChildReference.compile(
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100 new NameReference("node"),
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101 new ComponentReference()
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103 Accessor child = accessor.getComponent( ref );
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105 ChildReference ref = ChildReference.compile(
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106 new LabelReference("node"),
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107 new LabelReference("v")
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109 Accessor child = accessor.getComponent( ref );
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111 ChildReference ref = ChildReference.create("n-node/v");
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112 Accessor child = accessor.getComponent( ref );
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114 ChildReference ref = ChildReference.create("node/v");
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115 Accessor child = accessor.getComponent( ref );
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117 VariantAccessor va = recordAccessor.getFieldAccessor("node");
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118 Accessor child = va.getValueAccessor();
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121 ==Listening mechanism==
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122 Accessor offers a monitoring mechanism for the data model.
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123 There is an <code>[../javadoc/org/simantics/databoard/accessor/interestset/InterestSet.html|InterestSet]</code> that is a description of a sub-tree that is to be monitored of the data model.
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124 <code>[../javadoc/org/simantics/databoard/accessor/event/Event.html|Events]</code> are objects that spawned on changes to the data model. Each event object is annotated with [../javadoc/org/simantics/databoard/accessor/reference/index.html|reference path] that is in relation to the node where the listener was placed.
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126 Accessor Listeners use [EventThread Pattern] pattern.
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