derrickaw commented on code in PR #35952: URL: https://github.com/apache/beam/pull/35952#discussion_r2323161464
########## website/www/site/content/en/documentation/sdks/yaml-schema.md: ########## @@ -0,0 +1,119 @@ +--- +type: languages +title: "Apache Beam YAML Schema" +--- +<!-- + Licensed to the Apache Software Foundation (ASF) under one + or more contributor license agreements. See the NOTICE file + distributed with this work for additional information + regarding copyright ownership. The ASF licenses this file + to you under the Apache License, Version 2.0 (the + "License"); you may not use this file except in compliance + with the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, + software distributed under the License is distributed on an + "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY + KIND, either express or implied. See the License for the + specific language governing permissions and limitations + under the License. +--> + +# Beam YAML Schema + +As pipelines grow in size and complexity, it becomes more common to encounter +data that is malformed, doesn't meet preconditions, or otherwise causes issues +during processing. + +Beam YAML helps the user detect and capture these issues by using the optional +`output_schema` configuration, which is available for any transform in the YAML +SDK. For example, the following code creates a few "good" records and specifies +that the output schema from the `Create` transform should have records that +follow the expected schema: `sdk` as a string and `year` as an integer. + +```yaml +pipeline: + type: chain + transforms: + - type: Create + config: + elements: + - {sdk: MapReduce, year: 2004} + - {sdk: MillWheel, year: 2008} + output_schema: + type: object + properties: + sdk: + type: string + year: + type: integer + - type: AssertEqual + config: + elements: + - {sdk: MapReduce, year: 2004} + - {sdk: MillWheel, year: 2008} +``` + +However, a user will more likely want to detect and handle schema errors. If a +transform has a built-in error_handling configuration, the user can specify that +error_handling configuration and any errors found will be appended to the +transform error_handling output. For example, the following code will +create a few "good" and "bad" records with a specified schema of `user` as a +string and `timestamp` as a boolean. The `alice` row will fail in the standard +way because of not being an integer for the AssignTimestamps transform, while +the `bob` row will fail because after the AssignTimestamp transformation, the +output row will have the timestamp as an integer when it should be a boolean. + + +```yaml +pipeline: + type: composite + transforms: + - type: Create + name: CreateVisits + config: + elements: + - {user: alice, timestamp: "not-valid"} + - {user: bob, timestamp: 3} + - type: AssignTimestamps + input: CreateVisits + config: + timestamp: timestamp + error_handling: + output: invalid_rows + output_schema: + type: object + properties: + user: + type: string + timestamp: + type: boolean + - type: MapToFields + name: ExtractInvalidTimestamp + input: AssignTimestamps.invalid_rows + config: + language: python + fields: + user: "element.user" + timestamp: "element.timestamp" + - type: AssertEqual + input: ExtractInvalidTimestamp + config: + elements: + - {user: "alice", timestamp: "not-valid"} + - {user: bob, timestamp: 3} + - type: AssertEqual + input: AssignTimestamps + config: + elements: [] +``` + +WARNING: If a transform doesn't have the error_handling configuration available +and a user chooses to use this optional output_schema feature, any failures +found will result in the entire pipeline failing. If the user would still like +to have somekind of output schema validation, please use the ValidateWithSchema +transform instead. Review Comment: done, thanks -- 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. To unsubscribe, e-mail: github-unsubscr...@beam.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
