issue with Hive Serde dealing nested structs

问题:

I am trying to load a huge volume json data with nested structure to hive using a Json serde. some of the field names start with $ in nested structure. I am mapping hive filed names Using SerDeproperties, but how ever when i query the table, getting null in the field starting with $, tried with different syntax,but no luck.

Sample JSON:

{
    "_id" : "319FFE15FF90",
    "SomeThing" : 
    {
            "$SomeField"     : 22,
            "AnotherField"   : 2112,
            "YetAnotherField":    1
    }
 . . . etc . . . .

Using a schema as follows:

create table testSample
( 
    `_id` string, 
    something struct
    <
        $somefield:int,
        anotherfield:bigint, 
        yetanotherfield:int
    >
) 
row format serde 'org.openx.data.jsonserde.JsonSerDe' 
with serdeproperties
(
    "mapping.somefield" = "$somefield"
);

This schema builds OK, however, somefield(starting with $) in the above table is always returning null (all the other values exist and are correct).

We've been trying a lot of syntax combinations, but to no avail.

Does anyone know the trick to hap a nested field with a leading $ in its name?

回答1:

You almost got it right. Try creating the table like this. The mistake you're making is that when mapping in the serde properties (mapping.somefield ="$somefield") you're saying "when looking for the hive column named 'somefield', look for the json field '$somefield', but in hive you defined the column with the dollar sign, which if not outright illegal it's for sure not the best practice in hive.

create table testSample
(
`_id` string,
something struct
<
    somefield:int,
    anotherfield:bigint,
    yetanotherfield:int
  >
)
row format serde 'org.openx.data.jsonserde.JsonSerDe'
with serdeproperties
(
"mapping.somefield" = "$somefield"
);

I tested it with some test data:

{ "_id" : "123", "something": { "$somefield": 12, "anotherfield":13,"yetanotherfield":100}}
hive> select something.somefield from testSample;
OK
12

回答2:

I am suddenly starting to see this problem as well but for normal column names as well (no special characters such as $)

I am populating an external table (Temp) from another internal table (Table2) and want the output of Temp table in JSON format. I want column names in camel case in the output JSON file and so am also using the Serdepoperties in the Temp table to specify correct names. However, I am seeing that when I do Select * from the Temp table, it gives NULL values for the columns whose names have been used in the mapping.

I am running Hive 0.13. Here are the commands:

Create table command:

CREATE EXTERNAL TABLE Temp (
    data STRUCT<
        customerId:BIGINT, region:STRING, marketplaceId:INT, asin:ARRAY<STRING>>
) 
ROW FORMAT SERDE 'org.openx.data.jsonserde.JsonSerDe' 
WITH SERDEPROPERTIES ( 
    'mapping.customerid' = 'customerId',
    'mapping.marketplaceid' = 'marketplaceId'
) 
LOCATION '/output'; 

INSERT INTO TABLE Temp
    SELECT 
        named_struct ('customerId',customerId, 'region', region, 'marketplaceId', marketplaceId, 'asin', asin) 
    FROM Table2;

Select * from Temp:

{"customerid":null,"region":"EU","marketplaceid":null,"asin":["B000FC1PZC"]}
{"customerid":null,"region":"EU","marketplaceid":null,"asin":["B000FC1C9G"]}

See how "customerid" and "marketplaceid" are null. Generated JSON file is:

{"data":{"region":"EU","asin":["B000FC1PZC"]}}
{"data":{"region":"EU","asin":["B000FC1C9G"]}}

Now, if I remove the with serdeproperties, the table starts getting all values:

{"customerid":1,"region":"EU","marketplaceid":4,"asin":["B000FC1PZC"]}
{"customerid":2,"region":"EU","marketplaceid":4,"asin":["B000FC1C9G"]}

And then the JSON file so generated is:

{"data":{"region":"EU","marketplaceid":4,"asin":["B000FC1PZC"],"customerid":1}}
{"data":{"region":"EU","marketplaceid":4,"asin":["B000FC1C9G"],"customerid":2}}