将具有不同架构的json加载到PIG中 [英] Loading json with varying schema into PIG

问题描述

我遇到了将一组json文档加载到PIG中的问题. 我所拥有的是很多json文档，这些文档在它们具有的字段中各不相同，我需要的字段在大多数文档中，而在缺少空白的情况下，我想获取一个空值.

I ran into an issue loading a set json documents into PIG. What I have is a lot of json documents that all vary in the fields they have, the fields that I need are in most documents and in whare missing I would like to get a null value.

我刚刚下载并编译了最新的Pig版本(直接从apache git存储库下载了0.12)，以确保尚未解决此问题.

I just downloaded and compiled the latest Pig version (0.12 straight from the apache git repository) just to be sure this hasn't been solved yet.

我拥有的是一个像这样的json文档:

What I have is a json document like this:

{"foo":1,"bar":2,"baz":3}

当我使用此将其加载到PIG中时

When I load this into PIG using this

Json1 = LOAD 'test.json' USING JsonLoader('foo:int,bar:int,baz:int');
DESCRIBE Json1;
DUMP Json1;

我得到了预期的结果

Json1: {foo: int,bar: int,baz: int}
(1,2,3)

但是，当字段在模式中的顺序不同时:

However when the fields are in a different order in the schema :

Json2 = LOAD 'test.json' USING JsonLoader('baz:int,bar:int,foo:int');
DESCRIBE Json2;
DUMP Json2;

我得到了不希望的结果:

I get an undesired result:

Json2: {baz: int,bar: int,foo: int}
(1,2,3)

应该是

(3,2,1)

显然，架构定义中的字段名称与json中的字段名称无关.

Apparently the field names in the schema definition have nothing to do with the fieldnames in the json.

我需要的是将json文件(带有嵌入式文档！)中的特定字段加载到PIG中.

What I need is to load specific fields from a json file (with embedded documents!) into PIG.

我该如何解决?

推荐答案

我认为，即使是最新版本的Pig，这也是一个已知问题，因此除了使用功能更强大的JsonLoader之外，没有其他简便的方法

I think this is a known issue with even the latest version of Pig, so there isn't an easy way around this other than to use a more capable JsonLoader.

使用 Elephant Bird JSONLoader 代替，它将按照您期望的方式运行-换句话说，遵守字段顺序.

Use the Elephant Bird JSONLoader instead which will behave the way you expect - in other words respect field ordering.

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