Accessing the data
==================

.. highlight:: javascript

The types you use to write or read data may include nested structs, sequences 
and arrays of primitive types or structs, etc.

These types are defined in XML following the format of
`RTI's XML-Based Application Creation feature
<https://community.rti.com/static/documentation/connext-dds/current/doc/manuals/connext_dds_professional/xml_application_creation/index.htm#xml_based_app_creation_guide/UnderstandingXMLBased/XMLTagsConfigEntities.htm>`__.

To access the data, :class:`Instance` and :class:`SampleIterator` provide
setters and getters that expect a ``fieldName`` string, used to identify 
specific fields within the type. This section describes the format of this 
string.

We will use the following XML type definition of MyType:

.. code-block:: xml

    <types>
        <enum name="Color">
            <enumerator name="RED"/>
            <enumerator name="GREEN"/>
            <enumerator name="BLUE"/>
        </enum>
        <struct name= "Point">
            <member name="x" type="int32"/>
            <member name="y" type="int32"/>
        </struct>
        <union name="MyUnion">
            <discriminator type="nonBasic" nonBasicTypeName="Color"/>
            <case>
              <caseDiscriminator value="RED"/>
              <member name="point" type="nonBasic"  nonBasicTypeName= "Point"/>
            </case>
            <case>
              <caseDiscriminator value="GREEN"/>
              <member name="my_long" type="int32"/>
            </case>
        </union>
        <struct name= "MyType">
            <member name="my_long" type="int32"/>
            <member name="my_double" type="float64"/>
            <member name="my_enum" type="nonBasic"  nonBasicTypeName= "Color" default="GREEN"/>
            <member name="my_boolean" type="boolean" />
            <member name="my_point" type="nonBasic"  nonBasicTypeName= "Point"/>
            <member name="my_union" type="nonBasic"  nonBasicTypeName= "MyUnion"/>
            <member name="my_int_sequence" sequenceMaxLength="10" type="int32"/>
            <member name="my_point_sequence" sequenceMaxLength="10" type="nonBasic"  nonBasicTypeName= "Point"/>
            <member name="my_point_array" type="nonBasic"  nonBasicTypeName= "Point" arrayDimensions="3"/>
            <member name="my_optional_point" type="nonBasic"  nonBasicTypeName= "Point" optional="true"/>
            <member name="my_optional_long" type="int32" optional="true"/>
        </struct>
    </types>

Which corresponds to the following IDL definition:

.. code-block:: idl

    enum Color {
        RED,
        GREEN,
        BLUE
    };

    struct Point {
        long x;
        long y;
    };

    union MyUnion switch(Color) {
        case RED: Point point;
        case GREEN: string<512> my_string;
    };

    struct MyType {
        long my_long;
        double my_double;
        Color my_enum;
        boolean my_boolean;
        string<512> my_string;
        Point my_point;
        MyUnion my_union;
        sequence<long, 10> my_int_sequence;
        sequence<Point, 10> my_point_sequence;
        Point my_point_array[3];
        @optional Point my_optional_point;
        @optional long my_optional_long;
    };

.. hint::
    You can get the XML definition of an IDL file with 
    ``rtiddsgen -convertToXml MyType.idl``.

We will refer to an ``Output`` named ``output`` and
``Input`` named ``input`` such that ``input.samples.length > 0``.

Using JSON objects vs accessing individual members
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

On an Input or an Output, you can access the data all at once by using a 
JSON object, or member-by-member. Using a JSON object is usually more 
efficient if you intend to access most or all of the data members of 
a large type.

On an Output, :meth:`Instance.setFromJson` receives a JSON object with all, or
some, of the Output type members, and in an Input, 
:meth:`SampleIterator.getJson` retrieves all of the members.

It is also possible to provide a ``memberName`` to 
:meth:`SampleIterator.getJson` to obtain a JSON object containing the fields 
of that nested member only.

On the other hand, the methods described in the following section receive a
``fieldName`` argument to get or set a specific member.

Accessing basic members (numbers, strings and booleans)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

To set a field in an :class:`Output`, use the appropriate setter.

To set any numeric type, including enumerations:

.. code-block::

    output.instance.setNumber('my_long', 2)
    output.instance.setNumber('my_double', 2.14)
    output.instance.setNumber('my_enum', 2)

.. warning::
    The range of values for a numeric field is determined by the type
    used to define that field in the configuration file. However, 
    ``setNumber`` and ``getNumber`` can't handle 64-bit integers 
    (*int64* and *uint64*) whose absolute values are larger than 2^53. 
    This is a *Connector* limitation due to the use of *double* as an 
    intermediate representation.

    When ``setNumber`` or ``getNumber`` detect this situation, they will raise
    an :class:`DDSError`. ``getJson`` and ``setJson`` do not have this
    limitation and can handle any 64-bit integer.

To set booleans:

.. code-block::

    output.instance.setBoolean('my_boolean', True)

To set strings:

.. code-block::

    output.instance.setString('my_string', 'Hello, World!')

As an alternative to the previous setters, the type-independent method ``set``
can be used as follows:

.. code-block::

    // The set method works on all basic types
    output.instance.set('my_double', 2.14)
    output.instance.set('my_boolean', true)
    output.instance.set('my_string', 'Hello, World!')

In all cases, the type of the assigned value must be consistent with the type
of the field, as defined in the configuration file.

Similarly, to get a field in a :class:`Input` sample, use the appropriate
getter: :meth:`SampleIterator.getNumber()`, :meth:`SampleIterator.getBoolean()`,
:meth:`SampleIterator.getString()`, or the type-independent 
:meth:`SampleIterator.get()`.
``getString`` also works with numeric fields, returning the number as a string:

.. code-block::

    for (const sample of input.samples.validDataIter) {
        // Use the basic type specific getters
        let value = sample.getNumber('my_double')
        value = sample.getBoolean('my_boolean')
        value = sample.getString('my_string')

        // or alternatively, use the type-independent get method
        value = sample.get('my_double')
        value = sample.get('my_boolean')
        value = sample.get('my_string')

        // get a number as string:
        value = sample.getString('my_double')
    }


.. note::
    The typed getters and setters perform better than ``set``
    and ``get`` in applications that write or read at high rates.
    Also prefer ``getJson`` and ``setFromJson`` over ``set``
    and ``get`` when accessing all or most of the fields of a sample
    (see previous section).

.. note::
    If a field ``my_string``, defined as a string in the configuration file, contains
    a value that can be interpreted as a number, ``sample.get('my_string')`` returns
    a number, not a string.

Accessing structs
^^^^^^^^^^^^^^^^^

To access a nested member, use ``.`` to identify the fully-qualified ``fieldName``
and pass it to the corresponding setter or getter.

.. code-block::

    output.instance.setNumber('my_point.x', 10)
    output.instance.setNumber('my_point.y', 20)

    // alternatively:
    output.instance.set('my_point.x', 10)
    output.instance.set('my_point.y', 20)

It is possible to reset the value of a complex member back to its default:

.. code-block::

    output.instance.clearMember('my_point') // x and y are now 0

It is also possible to reset members using the ``set`` method:

.. code-block::

    output.instance.set('my_point', null)

Structs are set via JSON objects as follows:

.. code-block::

    output.instance.setFromJson({ 'my_point': { 'x':10, 'y':20 } })

When an member of a struct is not set, it retains its previous value. If we run
the following code after the previous call to ``setFromJson``:

.. code-block::

    output.instance.setFromJson({ 'my_point': { 'y': 200 } })

The value of ``my_point`` is now ``{ 'x': 10, 'y':200 }``. If you do not want 
the values to be retained you must clear the value first (as described above).

It is possible to obtain the JSON object of a nested struct:

.. code-block::

   for (const sample of input.samples.validDataIter) {
      let point = sample.getJson('my_point')
   }

``memberName`` must be one of the following types: array, sequence,
struct, value or union. If not, the call to ``getJson`` will fail:

.. code-block::

    for (let sample of input.samples.validDataIter) {
       try {
          let long = sample.getJson('my_long')
       } catch (err) {
          // Error was thrown since my_long is a basic type
       }
   }

It is also possible to obtain the JSON of a struct using the 
:meth:`SampleIterator.get` method:

.. code-block::

    for (const sample of input.samples.validDataIter) {
        let point = sample.get('my_point')
        // point is a JSON object
   }

The same limitations described in 
:ref:`Accessing basic members (numbers, strings and booleans)`
of using :meth:`SampleIterator.get` apply here.

Accessing arrays and sequences
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Use ``fieldName[index]`` to access an element of a sequence or array,
where ``0 <= index < length``:

.. code-block::

    let value = input.samples.get(0).getNumber('my_int_sequence[1]')
    value = input.samples.get(0).getNumber('my_point_sequence[2].y')

To obtain the length of a sequence in an :class:`Input` sample, 
append ``#`` to the ``fieldName``:

.. code-block::

    let length = input.samples[0].getNumber('my_int_sequence#')

Another option is to use ``SampleIterator.getJson('fieldName')`` to obtain
a JSON object containing all of the elements of the array or sequence with 
name ``fieldName``:

.. code-block::

    for (let sample of input.samples.validDataIter) {
        let thePointSequence = sample.getJson('my_point_sequence')
    }

You can also get a specific element as a dictionary (if the element type 
is complex):

.. code-block::

   for (let sample of input.samples.validDataIter) {
      let pointElement = sample.getJson('my_point_sequence[1]')
   }

In an :class:`Output`, sequences are automatically resized:

.. code-block::

    output.instance.setNumber('my_int_sequence[5]', 10) // length is now 6
    output.instance.setNumber('my_int_sequence[4]', 9) // length still 6

You can clear a sequence:

.. code-block::

    output.instance.clearMember('my_int_sequence') // my_int_sequence is now empty

In JSON objects, sequences and arrays are represented as lists. For example:

.. code-block::

    output.instance.setFromJson({
        my_int_sequence: [1, 2],
        my_point_sequence: [{ x: 1, y: 1 }, { x: 2, y: 2 }]
    })

Arrays have a constant length that can't be changed. When you don't set all 
the elements of an array, the remaining elements retain their previous values. 
However, sequences are always overwritten. See the following example:

.. code-block::

    output.instance.setFromJson({
        my_point_sequence: [{ x: 1, y: 1 }, { x: 2, y: 2 }],
        my_point_array: [{ x: 1, y: 1 }, { x: 2, y: 2 }, { x: 3, y: 3 }] })

    output.instance.setFromJson({
        my_point_sequence: [{ x: 100 }],
        my_point_array: [{ x: 100}, { y: 200}] })

After the second call to ``setFromJson``, the contents of ``my_point_sequence``
are ``[{ x: 100, y: 0 }]``, but the contents of ``my_point_array`` are:
``[{ x: 100, y: 1 }, { x: 2, y: 200 }, {x: 3, y: 3 }]``.

Accessing optional members
^^^^^^^^^^^^^^^^^^^^^^^^^^

A optional member is a member that applications can decide to send or not as
part of every published sample. Therefore, optional members may have a value 
or not. They are accessed the same way as non-optional members, except that 
``null`` is a possible value.

On an Input, any of the getters may return ``null`` if the field is optional:

.. code-block::

    if (input.samples.get(0).getNumber('my_optional_long') == null) {
        console.log('my_optional_long not set')
    }

    if (input.samples.get(0).getNumber('my_optional_point.x') == null) {
        console.log('my_optional_point not set')
    }

:meth:`SampleIterator.getJson()` returns a JSON object that doesn't include unset
optional members.

To set an optional member on an Output:

.. code-block::

    output.instance.setNumber('my_optional_long', 10)

If the type of the optional member is not primitive, when any of its members is
first set, the rest are initialized to their default values:

.. code-block::

    output.instance.setNumber('my_optional_point.x', 10)

If ``my_optional_point`` was not previously set, the previous code also sets
``y`` to 0.

There are several ways to reset an optional member. If the type is primitive:

.. code-block::

    output.instance.setNumber('my_optional_long', null) // Option 1
    output.instance.clearMember('my_optional_long') // Option 2
    output.instance.set('my_optional_long', null) // Option 3

If the member type is complex, all the above options except option 1 are 
available:

.. code-block::

    output.instance.clearMember('my_optional_point')
    output.instance.set('my_optional_point', null)

Note that :meth:`Instance.setFromJson()` doesn't clear those members that are
not specified; their values remain. For example:

.. code-block::

    output.instance.setNumber('my_optional_long', 5)
    output.instance.setFromJson({ my_double: 3.3, my_long: 4 })
    // my_optional_long is still 5

To clear a member, set it to ``null`` explicitly::

    output.instance.setFromJson({ my_double: 3.3, my_long: 4, my_optional_long: null })


For more information about optional members in DDS, see the 
*Getting Started Guide Addendum for Extensible Types*,
`Optional Members 
<https://community.rti.com/static/documentation/connext-dds/current/doc/manuals/connext_dds_professional/extensible_types_guide/index.htm#extensible_types/Optional_Members.htm>`__. 

Accessing unions
^^^^^^^^^^^^^^^^

In an :class:`Output`, the union member is automatically selected when you 
set it:

.. code-block::

    output.instance.setNumber('my_union.point.x', 10)

You can change it later:

.. code-block::

    output.instance.setNumber('my_union.my_long', 10)

In an :class:`Input`, you can obtain the selected member as a string::

    if (input.samples.get(0).getString('my_union#') == 'point') {
        value = input.samples.get(0).getNumber('my_union.point.x')
    }

Accessing key values of disposed samples
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Using :meth:`Output.write`, an :class:`Output` can write data, or dispose or 
unregister an instance.
Depending on which of these operations is performed, the ``instance_state`` of the
received sample will be ``'ALIVE'``, ``'NOT_ALIVE_NO_WRITERS'`` or ``'NOT_ALIVE_DISPOSED'``.
If the instance was disposed, this ``instance_state`` will be ``'NOT_ALIVE_DISPOSED'``.
In this state, it is possible to access the key fields of the instance that was disposed.

.. note::
    :attr:`SampleInfo.valid_data` will be false when the :attr:`SampleInfo.instance_state`
    is ``'NOT_ALIVE_DISPOSED'``. In this situation it's possible to access the
    key fields in the received sample.

The key fields can be accessed as follows:

.. code-block::

    // The output and input are using the following type:
    // struct ShapeType {
    //     @key string<128> color;
    //     long x;
    //     long y;
    //     long shapesize;
    // }

    output.instance.set('x', 4)
    output.instance.set('color', 'Green')
    // Assume that some data associated with this instance has already been sent
    output.write({ action: 'dispose' })
    await input.wait()
    input.take()
    let sample = input.samples.get(0)

    if (sample.info.get('instance_state') === 'NOT_ALIVE_DISPOSED') {
        // sample.info.get('valid_data') will be false in this situation
        // Only the key-fields should be accessed
        let color = sample.get('color') // 'Green'
        // The fields 'x','y' and 'shapesize' cannot be retrieved because they're
        // not part of the key
        // You can also call getJson() to get all of the key fields in a JSON object.
        // Again, only the key fields returned within the JSON object should
        // be used.
        let keyValues = sample.getJson() // { color: 'Green', x: 0, y: 0, shapesize: 0 }
    }

.. warning::
    When the sample has an instance state of ``'NOT_ALIVE_DISPOSED'`` only the
    key fields should be accessed.