apache-pig - 创建 pig udf 架构时遇到问题

Question

试图解析 xml，但我的 UDF 返回元组时遇到问题。遵循 http://verboselogging.com/2010/03/31/writing-user-defined-functions-for-pig 中的示例

pig 脚本

titles = FOREACH programs GENERATE (px.pig.udf.PARSE_KEYWORDS(program))
    AS (root_id:chararray, keyword:chararray);

这是输出架构代码:

 override def outputSchema(input: Schema): Schema = {
    try {
      val s: Schema = new Schema
      s.add(new Schema.FieldSchema("root_id", DataType.CHARARRAY))
      s.add(new Schema.FieldSchema("keyword", DataType.CHARARRAY))
      return s
    }
    catch {
      case e: Exception => {
        return null
      }
    }
  }

我收到这个错误

pig script failed to validate: org.apache.pig.impl.logicalLayer.FrontendException: 
ERROR 0: Given UDF returns an improper Schema. 
Schema should only contain one field of a Tuple, Bag, or a single type. 
Returns: {root_id: chararray,keyword: chararray}

更新最终解决方案:

在 Java 中

public Schema outputSchema(Schema input) {
    try {
        Schema tupleSchema = new Schema();
        tupleSchema.add(input.getField(1));
        tupleSchema.add(input.getField(0));
        return new Schema(new Schema.FieldSchema(getSchemaName(this.getClass().getName().toLowerCase(),  input),tupleSchema, DataType.TUPLE));
    } catch (Exception e) {
        return null;
    }
}

Answer 1

您需要添加您的 s模式实例变量到另一个 Schema 对象。

尝试返回 new Schema(new FieldSchema(..., input), s, DataType.TUPLE));就像下面的模板:

这是我在 Java 中的回答(填写您的变量名):

@Override
    public Schema outputSchema(Schema input) {
        Schema tupleSchema = new Schema();
        try {

            tupleSchema.add(new FieldSchema("root_id", DataType.CHARARRAY));
            tupleSchema.add(new FieldSchema("keyword", DataType.CHARARRAY));

            return new Schema(new FieldSchema(getSchemaName(this.getClass().getName().toLowerCase(), input), tupleSchema, DataType.TUPLE));
        } catch (FrontendException e) {
            e.printStackTrace();
            return null;
        }
    }

你会尝试:

titles = FOREACH programs GENERATE (px.pig.udf.PARSE_KEYWORDS(program));

如果没有出错，请尝试:

titles = FOREACH TITLES GENERATE
    $0 AS root_id
    ,$1 AS keyword
;

并告诉我错误？