Google Dataflow:用于BigQuery插入的PCollection <String>到PCollection <TableRow>

Question

我是Google Cloud Platform的新手,我第一次尝试使用Google Dataflow来完成我的研究生课程项目.我想要做的是编写一个自动加载作业,从我的云存储中的某个存储桶加载文件,并将其中的数据插入到BigQuery表中.

我将数据作为PCollection<String>类型获取,但是为了插入BigQuery,我显然需要将其转换为PCollection<TableRow>类型.到目前为止,我还没有找到一个可靠的答案.

这是我的代码:

public static void main(String[] args) {
    //Defining the schema of the BigQuery table
    List<TableFieldSchema> fields = new ArrayList<>();
    fields.add(new TableFieldSchema().setName("Datetime").setType("TIMESTAMP"));
    fields.add(new TableFieldSchema().setName("Consumption").setType("FLOAT"));
    fields.add(new TableFieldSchema().setName("MeterID").setType("STRING"));
    TableSchema schema = new TableSchema().setFields(fields);

    //Creating the pipeline
    PipelineOptions options = PipelineOptionsFactory.fromArgs(args).withValidation().create();
    Pipeline p = Pipeline.create(options);

    //Getting the data from cloud storage
    PCollection<String> lines = p.apply(TextIO.Read.named("ReadCSVFromCloudStorage").from("gs://mybucket/myfolder/certainCSVfile.csv"));

    //Probably need to do some transform here ...

    //Inserting data into BigQuery
    lines.apply(BigQueryIO.Write
            .named("WriteToBigQuery")
            .to("projectID:datasetID:tableID")
            .withSchema(schema)
            .withWriteDisposition(BigQueryIO.Write.WriteDisposition.WRITE_APPEND)
            .withCreateDisposition(BigQueryIO.Write.CreateDisposition.CREATE_IF_NEEDED));
}

我可能只是忘记了一些基本的东西,所以我希望你们可以帮助我...

Answer 1

BigQueryIO.Write按照写给BigQuery的PCollection<TableRow>概述进行操作.您需要应用转换才能转换为.举个例子,看一下StringToRowConverter:PCollection<TableRow>PCollection<String>

  static class StringToRowConverter extends DoFn<String, TableRow> {
    /**
     * In this example, put the whole string into single BigQuery field.
     */
    @Override
    public void processElement(ProcessContext c) {
      c.output(new TableRow().set("string_field", c.element()));
    }
  ...
}