damccorm commented on code in PR #30420: URL: https://github.com/apache/beam/pull/30420#discussion_r1511490419
########## learning/prompts/documentation-lookup-nolinks/34_change_coders_data_encoding.md: ########## @@ -0,0 +1,107 @@ +Prompt: +How to get, set, and create new coders for my Apache Beam pipeline? + +Response: +Every `PCollection` in an Apache Beam pipeline requires a corresponding `Coder`. In most cases, the Apache Beam SDKs can automatically infer a `Coder` for a `PCollection` based on its element type or the producing transform. However, in some instances, you may need to explicitly set a `Coder` or create a custom `Coder`. + +In the Apache Beam SDKs for Python and Java, the `Coder` type provides the necessary methods for encoding and decoding data. To get, set, or register a coder for a particular pipeline, you can access and modify the pipeline’s `CoderRegistry` object. + +The following examples demonstrate how to get, set, and create a new `Coder` in an Apache Beam pipeline using the Python and Java SDKs. + +**Python SDK:** + +In the Python SDK, you can use the following methods: +* `coders.registry`: retrieves the pipeline’s `CoderRegistry` object. +* `CoderRegistry.get_coder`: retrieves the default `Coder` for a type. +* `CoderRegistry.register_coder`: sets a new `Coder` for the target type. + +Here is an example illustrating how to set the default `Coder` in the Python SDK: + +```python +apache_beam.coders.registry.register_coder(int, BigEndianIntegerCoder) +``` + +The provided example sets a default `Coder`, specifically `BigEndianIntegerCoder`, for `int` values in the pipeline. + +For custom or complex nested data types, you can implement a custom coder for your pipeline. To create a new `Coder`, you need to define a class that inherits from `Coder` and implement the required methods: +* `encode`: takes input values and encodes them into byte strings. +* `decode`: decodes the encoded byte string into its corresponding object. +* `is_deterministic`: specifies whether this coder encodes values deterministically or not. A deterministic coder produces the same encoded representation of a given object every time, even if it is called on different workers at different moments. The method returns `True` or `False` based on your implementation. + +Here is an example of a custom `Coder` implementation in the Python SDK: + +```python +from apache_beam.coders import Coder + +class CustomCoder(Coder): + def encode(self, value): + # Implementation for encoding 'value' into byte strings + pass + + def decode(self, encoded): + # Implementation for decoding byte strings into the original object + pass + + def is_deterministic(self): + # Specify whether this coder produces deterministic encodings + return True # or False based on your implementation +``` + +**Java SDK:** + +In the Java SDK, you can use the following methods: +* `Pipeline.getCoderRegistry`: retrieves the pipeline’s `CoderRegistry` object. +* `getCoder`: retrieves the coder for an existing `PCollection`. +* `CoderRegistry.getCoder`: retrieves the default `Coder` for a type. +* `CoderRegistry.registerCoder`: sets a new default `Coder` for the target type. + +Here is an example of how you can set the default ‘Coder’ in the Java SDK: + +```java +PipelineOptions options = PipelineOptionsFactory.create(); +Pipeline p = Pipeline.create(options); + +CoderRegistry cr = p.getCoderRegistry(); +cr.registerCoder(Integer.class, BigEndianIntegerCoder.class); +``` + +In this example, you use the method `CoderRegistry.registerCoder` to register `BigEndianIntegerCoder` for the target `integer` type. + +For custom or complex nested data types, you can implement a custom coder for your pipeline. For this, the `Coder` class exposes the following key methods: +* `encode`: takes input values and encodes them into byte strings. +* `decode`: decodes the encoded byte string into its corresponding object. +* `verifyDeterministic`: specifies whether this coder produces deterministic encodings. A deterministic coder produces the same encoded representation of a given object every time, even if it is called on different workers at different moments. The method will return `NonDeterministicException` if a coder is not deterministic. + +Here’s an example of a custom `Coder` implementation in the Java SDK: + +```java +import org.apache.beam.sdk.coders.Coder; +import org.apache.beam.sdk.coders.CoderException; +import org.apache.beam.sdk.coders.CoderRegistry; +import org.apache.beam.sdk.coders.InstantCoder; +import org.apache.beam.sdk.coders.StructuredCoder; +import org.joda.time.Instant; +import java.io.IOException; +import java.io.InputStream; +import java.io.OutputStream; Review Comment: ```suggestion import org.apache.beam.sdk.coders.CoderException; import org.apache.beam.sdk.coders.StructuredCoder; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; ``` We don't use several of these imports, so we can simplify here. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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