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| <blockquote> |
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| <div class="section" id="creating-a-custom-operator"> |
| <h1>Creating a custom Operator<a class="headerlink" href="#creating-a-custom-operator" title="Permalink to this headline">¶</a></h1> |
| <p>Airflow allows you to create new operators to suit the requirements of you or your team. |
| The extensibility is one of the many reasons which makes Apache Airflow powerful.</p> |
| <p>You can create any operator you want by extending the <a class="reference internal" href="../_api/airflow/models/baseoperator/index.html#airflow.models.baseoperator.BaseOperator" title="airflow.models.baseoperator.BaseOperator"><code class="xref py py-class docutils literal notranslate"><span class="pre">airflow.models.baseoperator.BaseOperator</span></code></a></p> |
| <p>There are two methods that you need to override in a derived class:</p> |
| <ul class="simple"> |
| <li><p>Constructor - Define the parameters required for the operator. You only need to specify the arguments specific to your operator. |
| Use <code class="docutils literal notranslate"><span class="pre">@apply_defaults</span></code> decorator function to fill unspecified arguments with <code class="docutils literal notranslate"><span class="pre">default_args</span></code>. You can specify the <code class="docutils literal notranslate"><span class="pre">default_args</span></code> |
| in the dag file. See <a class="reference internal" href="../concepts.html#default-args"><span class="std std-ref">Default args</span></a> for more details.</p></li> |
| <li><p>Execute - The code to execute when the runner calls the operator. The method contains the |
| airflow context as a parameter that can be used to read config values.</p></li> |
| </ul> |
| <p>Let’s implement an example <code class="docutils literal notranslate"><span class="pre">HelloOperator</span></code> in a new file <code class="docutils literal notranslate"><span class="pre">hello_operator.py</span></code>:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">airflow.models.baseoperator</span> <span class="kn">import</span> <span class="n">BaseOperator</span> |
| <span class="kn">from</span> <span class="nn">airflow.utils.decorators</span> <span class="kn">import</span> <span class="n">apply_defaults</span> |
| |
| <span class="k">class</span> <span class="nc">HelloOperator</span><span class="p">(</span><span class="n">BaseOperator</span><span class="p">):</span> |
| |
| <span class="nd">@apply_defaults</span> |
| <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span> |
| <span class="bp">self</span><span class="p">,</span> |
| <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> |
| <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span> <span class="o">-></span> <span class="kc">None</span><span class="p">:</span> |
| <span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__init__</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span> |
| <span class="bp">self</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="n">name</span> |
| |
| <span class="k">def</span> <span class="nf">execute</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">context</span><span class="p">):</span> |
| <span class="n">message</span> <span class="o">=</span> <span class="s2">"Hello </span><span class="si">{}</span><span class="s2">"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">name</span><span class="p">)</span> |
| <span class="nb">print</span><span class="p">(</span><span class="n">message</span><span class="p">)</span> |
| <span class="k">return</span> <span class="n">message</span> |
| </pre></div> |
| </div> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>For imports to work, you should place the file in a directory that |
| is present in the <code class="docutils literal notranslate"><span class="pre">PYTHONPATH</span></code> env. Airflow adds <code class="docutils literal notranslate"><span class="pre">dags/</span></code>, <code class="docutils literal notranslate"><span class="pre">plugins/</span></code>, and <code class="docutils literal notranslate"><span class="pre">config/</span></code> directories |
| in the Airflow home to <code class="docutils literal notranslate"><span class="pre">PYTHONPATH</span></code> by default. e.g., In our example, |
| the file is placed in the <code class="docutils literal notranslate"><span class="pre">custom_operator</span></code> directory.</p> |
| </div> |
| <p>You can now use the derived custom operator as follows:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">custom_operator.hello_operator</span> <span class="kn">import</span> <span class="n">HelloOperator</span> |
| |
| <span class="k">with</span> <span class="n">dag</span><span class="p">:</span> |
| <span class="n">hello_task</span> <span class="o">=</span> <span class="n">HelloOperator</span><span class="p">(</span><span class="n">task_id</span><span class="o">=</span><span class="s1">'sample-task'</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s1">'foo_bar'</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <div class="section" id="hooks"> |
| <h2>Hooks<a class="headerlink" href="#hooks" title="Permalink to this headline">¶</a></h2> |
| <p>Hooks act as an interface to communicate with the external shared resources in a DAG. |
| For example, multiple tasks in a DAG can require access to a MySQL database. Instead of |
| creating a connection per task, you can retrieve a connection from the hook and utilize it. |
| Hook also helps to avoid storing connection auth parameters in a DAG. |
| See <a class="reference internal" href="connection/index.html"><span class="doc">Managing Connections</span></a> for how to create and manage connections.</p> |
| <p>Let’s extend our previous example to fetch name from MySQL:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">HelloDBOperator</span><span class="p">(</span><span class="n">BaseOperator</span><span class="p">):</span> |
| |
| <span class="nd">@apply_defaults</span> |
| <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span> |
| <span class="bp">self</span><span class="p">,</span> |
| <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> |
| <span class="n">mysql_conn_id</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> |
| <span class="n">database</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> |
| <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span> <span class="o">-></span> <span class="kc">None</span><span class="p">:</span> |
| <span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__init__</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span> |
| <span class="bp">self</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="n">name</span> |
| <span class="bp">self</span><span class="o">.</span><span class="n">mysql_conn_id</span> <span class="o">=</span> <span class="n">mysql_conn_id</span> |
| <span class="bp">self</span><span class="o">.</span><span class="n">database</span> <span class="o">=</span> <span class="n">database</span> |
| |
| <span class="k">def</span> <span class="nf">execute</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">context</span><span class="p">):</span> |
| <span class="n">hook</span> <span class="o">=</span> <span class="n">MySqlHook</span><span class="p">(</span><span class="n">mysql_conn_id</span><span class="o">=</span><span class="bp">self</span><span class="o">.</span><span class="n">mysql_conn_id</span><span class="p">,</span> |
| <span class="n">schema</span><span class="o">=</span><span class="bp">self</span><span class="o">.</span><span class="n">database</span><span class="p">)</span> |
| <span class="n">sql</span> <span class="o">=</span> <span class="s2">"select name from user"</span> |
| <span class="n">result</span> <span class="o">=</span> <span class="n">hook</span><span class="o">.</span><span class="n">get_first</span><span class="p">(</span><span class="n">sql</span><span class="p">)</span> |
| <span class="n">message</span> <span class="o">=</span> <span class="s2">"Hello </span><span class="si">{}</span><span class="s2">"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">result</span><span class="p">[</span><span class="s1">'name'</span><span class="p">])</span> |
| <span class="nb">print</span><span class="p">(</span><span class="n">message</span><span class="p">)</span> |
| <span class="k">return</span> <span class="n">message</span> |
| </pre></div> |
| </div> |
| <p>When the operator invokes the query on the hook object, a new connection gets created if it doesn’t exist. |
| The hook retrieves the auth parameters such as username and password from Airflow |
| backend and passes the params to the <a class="reference internal" href="../_api/airflow/hooks/base_hook/index.html#airflow.hooks.base_hook.BaseHook.get_connection" title="airflow.hooks.base_hook.BaseHook.get_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">airflow.hooks.base_hook.BaseHook.get_connection()</span></code></a>. |
| You should create hook only in the <code class="docutils literal notranslate"><span class="pre">execute</span></code> method or any method which is called from <code class="docutils literal notranslate"><span class="pre">execute</span></code>. |
| The constructor gets called whenever Airflow parses a DAG which happens frequently. |
| The <code class="docutils literal notranslate"><span class="pre">execute</span></code> gets called only during a DAG run.</p> |
| </div> |
| <div class="section" id="user-interface"> |
| <h2>User interface<a class="headerlink" href="#user-interface" title="Permalink to this headline">¶</a></h2> |
| <p>Airflow also allows the developer to control how the operator shows up in the DAG UI. |
| Override <code class="docutils literal notranslate"><span class="pre">ui_color</span></code> to change the background color of the operator in UI. |
| Override <code class="docutils literal notranslate"><span class="pre">ui_fgcolor</span></code> to change the color of the label.</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">HelloOperator</span><span class="p">(</span><span class="n">BaseOperator</span><span class="p">):</span> |
| <span class="n">ui_color</span> <span class="o">=</span> <span class="s1">'#ff0000'</span> |
| <span class="n">ui_fgcolor</span> <span class="o">=</span> <span class="s1">'#000000'</span> |
| <span class="o">....</span> |
| </pre></div> |
| </div> |
| </div> |
| <div class="section" id="templating"> |
| <h2>Templating<a class="headerlink" href="#templating" title="Permalink to this headline">¶</a></h2> |
| <p>You can use <a class="reference internal" href="../concepts.html#jinja-templating"><span class="std std-ref">Jinja templates</span></a> to parameterize your operator. |
| Airflow considers the field names present in <code class="docutils literal notranslate"><span class="pre">template_fields</span></code> for templating while rendering |
| the operator.</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">HelloOperator</span><span class="p">(</span><span class="n">BaseOperator</span><span class="p">):</span> |
| |
| <span class="n">template_fields</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'name'</span><span class="p">]</span> |
| |
| <span class="nd">@apply_defaults</span> |
| <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span> |
| <span class="bp">self</span><span class="p">,</span> |
| <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> |
| <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span> <span class="o">-></span> <span class="kc">None</span><span class="p">:</span> |
| <span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__init__</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span> |
| <span class="bp">self</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="n">name</span> |
| |
| <span class="k">def</span> <span class="nf">execute</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">context</span><span class="p">):</span> |
| <span class="n">message</span> <span class="o">=</span> <span class="s2">"Hello from </span><span class="si">{}</span><span class="s2">"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">name</span><span class="p">)</span> |
| <span class="nb">print</span><span class="p">(</span><span class="n">message</span><span class="p">)</span> |
| <span class="k">return</span> <span class="n">message</span> |
| </pre></div> |
| </div> |
| <p>You can use the template as follows:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="n">dag</span><span class="p">:</span> |
| <span class="n">hello_task</span> <span class="o">=</span> <span class="n">HelloOperator</span><span class="p">(</span><span class="n">task_id</span><span class="o">=</span><span class="s1">'task_id_1'</span><span class="p">,</span> <span class="n">dag</span><span class="o">=</span><span class="n">dag</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s1">'{{ task_id }}'</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>In this example, Jinja looks for the <code class="docutils literal notranslate"><span class="pre">name</span></code> parameter and substitutes <code class="docutils literal notranslate"><span class="pre">{{</span> <span class="pre">task_id</span> <span class="pre">}}</span></code> with |
| <code class="docutils literal notranslate"><span class="pre">task_id_1</span></code>.</p> |
| <p>The parameter can also contain a file name, for example, a bash script or a SQL file. You need to add |
| the extension of your file in <code class="docutils literal notranslate"><span class="pre">template_ext</span></code>. If a <code class="docutils literal notranslate"><span class="pre">template_field</span></code> contains a string ending with |
| the extension mentioned in <code class="docutils literal notranslate"><span class="pre">template_ext</span></code>, Jinja reads the content of the file and replace the templates |
| with actual value. Note that Jinja substitutes the operator attributes and not the args.</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">HelloOperator</span><span class="p">(</span><span class="n">BaseOperator</span><span class="p">):</span> |
| |
| <span class="n">template_fields</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'guest_name'</span><span class="p">]</span> |
| |
| <span class="nd">@apply_defaults</span> |
| <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span> |
| <span class="bp">self</span><span class="p">,</span> |
| <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> |
| <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span> <span class="o">-></span> <span class="kc">None</span><span class="p">:</span> |
| <span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__init__</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span> |
| <span class="bp">self</span><span class="o">.</span><span class="n">guest_name</span> <span class="o">=</span> <span class="n">name</span> |
| </pre></div> |
| </div> |
| <p>In the example, the <code class="docutils literal notranslate"><span class="pre">template_fields</span></code> should be <code class="docutils literal notranslate"><span class="pre">['guest_name']</span></code> and not <code class="docutils literal notranslate"><span class="pre">['name']</span></code></p> |
| </div> |
| <div class="section" id="define-an-operator-extra-link"> |
| <h2>Define an operator extra link<a class="headerlink" href="#define-an-operator-extra-link" title="Permalink to this headline">¶</a></h2> |
| <p>For your operator, you can <a class="reference internal" href="define_extra_link.html"><span class="doc">Define an extra link</span></a> that can |
| redirect users to external systems. For example, you can add a link that redirects |
| the user to the operator’s manual.</p> |
| </div> |
| </div> |
| |
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| </div> |
| |
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