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| |
| <html> |
| <h2>Side Input</h2> |
| <p> |
| In addition to the main input PCollection, you can provide additional inputs to a ParDo transform |
| in the form of side inputs. A side input is an additional input that your DoFn can access each |
| time it processes an element in the input PCollection. When you specify a side input, you create |
| a view of some other data that can be read from within the ParDo transform’s DoFn while |
| processing each element. |
| </p> |
| <p> |
| Side inputs are useful if your ParDo needs to inject additional data when processing each element |
| in the input PCollection, but the additional data needs to be determined at runtime (and not |
| hard-coded). Such values might be determined by the input data, or depend on a different branch |
| of your pipeline. |
| </p> |
| <p> |
| <b>Kata:</b> Please enrich each Person with the country based on the city he/she lives in. |
| </p> |
| <br> |
| <div class="hint"> |
| Use <a href="https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/transforms/View.html"> |
| View</a> to create PCollectionView of citiesToCountries. |
| </div> |
| <div class="hint"> |
| Use <a href="https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/transforms/ParDo.html"> |
| ParDo</a> with <a href="https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/transforms/DoFn.html"> |
| DoFn</a> that accepts |
| <a href="https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/transforms/ParDo.SingleOutput.html#withSideInputs-org.apache.beam.sdk.values.PCollectionView...-"> |
| side input</a>. |
| </div> |
| <div class="hint"> |
| Refer to the Beam Programming Guide |
| <a href="https://beam.apache.org/documentation/programming-guide/#side-inputs">"Side inputs"</a> |
| section for more information. |
| </div> |
| </html> |
