Question

我有一个从pubsub获得的对象的PCollection，可以说：

 PCollection<Student> pStudent ;

在学生属性中，有一个属性，比如说studentID；并且我想使用此学生ID从BigQuery读取属性（class_code），并将我从BQ获取的class_code设置为PCollcetion中的Student对象

有人知道如何实现吗？我知道在Beam中有一个 BigQueryIO ，但是如果我要在BQ中执行的查询字符串条件来自PCollection中的学生对象（studentID），以及如何执行该操作，该怎么办呢？可以从BigQuery的结果中将值设置为PCollection吗？

Answer 1

我考虑过两种选择。一个可能是使用BigQueryIO读取整个表并将其具体化为边输入，或者使用CoGroupByKey来合并所有数据。我在本文中实现的另一种可能性是直接使用Java客户端库。

我使用以下方法创建了一些虚拟数据：

$ bq mk test.students name:STRING,grade:STRING
$ bq query --use_legacy_sql=false 'insert into test.students (name, grade) values ("Yoda", "A+"), ("Leia", "B+"), ("Luke", "C-"), ("Chewbacca", "F")'

如下所示：

，然后在管道中，生成一些输入虚拟数据：

Create.of("Luke", "Leia", "Yoda", "Chewbacca")

对于每个“学生”，我都按照this example中的方法在BigQuery表中获取相应的成绩。根据之前的注释，根据您的数据量，费率（配额）和成本考虑因素进行考虑。完整示例：

public class DynamicQueries {

    private static final Logger LOG = LoggerFactory.getLogger(DynamicQueries.class);

    @SuppressWarnings("serial")
    public static void main(String[] args) {
        PipelineOptions options = PipelineOptionsFactory.fromArgs(args).create();
        Pipeline p = Pipeline.create(options);

        // create input dummy data     
        PCollection<String> students = p.apply("Read students data", Create.of("Luke", "Leia", "Yoda", "Chewbacca").withCoder(StringUtf8Coder.of()));

        // ParDo to map each student with the grade in BigQuery
        PCollection<KV<String, String>> marks = students.apply("Read marks from BigQuery", ParDo.of(new DoFn<String, KV<String, String>>() {
            @ProcessElement
            public void processElement(ProcessContext c) throws Exception {
                BigQuery bigquery = BigQueryOptions.getDefaultInstance().getService();

                QueryJobConfiguration queryConfig =
                    QueryJobConfiguration.newBuilder(
                      "SELECT name, grade "
                          + "FROM `PROJECT_ID.test.students` "
                          + "WHERE name = "
                          + "\"" + c.element() + "\" "  // fetch the appropriate student
                          + "LIMIT 1")
                        .setUseLegacySql(false) // Use standard SQL syntax for queries.
                        .build();

                // Create a job ID so that we can safely retry.
                JobId jobId = JobId.of(UUID.randomUUID().toString());
                Job queryJob = bigquery.create(JobInfo.newBuilder(queryConfig).setJobId(jobId).build());

                // Wait for the query to complete.
                queryJob = queryJob.waitFor();

                // Check for errors
                if (queryJob == null) {
                  throw new RuntimeException("Job no longer exists");
                } else if (queryJob.getStatus().getError() != null) {
                  throw new RuntimeException(queryJob.getStatus().getError().toString());
                }

                // Get the results.
                QueryResponse response = bigquery.getQueryResults(jobId)
                TableResult result = queryJob.getQueryResults();

                String mark = new String();

                for (FieldValueList row : result.iterateAll()) {
                    mark = row.get("grade").getStringValue();
                }

                c.output(KV.of(c.element(), mark));
            }
        }));

        // log to check everything is right
        marks.apply("Log results", ParDo.of(new DoFn<KV<String, String>, KV<String, String>>() {
            @ProcessElement
            public void processElement(ProcessContext c) throws Exception {
                LOG.info("Element: " + c.element().getKey() + " " + c.element().getValue());
                c.output(c.element());
            }
        }));

        p.run();
    }
}

输出为：

Nov 08, 2018 2:17:16 PM com.dataflow.samples.DynamicQueries$2 processElement
INFO: Element: Yoda A+
Nov 08, 2018 2:17:16 PM com.dataflow.samples.DynamicQueries$2 processElement
INFO: Element: Luke C-
Nov 08, 2018 2:17:16 PM com.dataflow.samples.DynamicQueries$2 processElement
INFO: Element: Chewbacca F
Nov 08, 2018 2:17:16 PM com.dataflow.samples.DynamicQueries$2 processElement
INFO: Element: Leia B+

（已使用BigQuery 1.22.0和2.5.0 Java SDK for Dataflow进行了测试）

如何从Dataflow中的PCollection读取bigQuery

1 个答案: