Attributes lost after running SelectHiveQL

[#1]

Attributes lost after running SelectHiveQL, do you know why? Is it a bug? And how to fix it?

I have some attributes updated before SelectHiveQL, but all the attributes set disappear after running SelectHiveQL, please help.

[#2 · Accepted solution]

@adam chui

As per the documentation of SelectHiveQL processor states that If it is triggered by an incoming FlowFile, then attributes of that FlowFile will be available when evaluating the select query. FlowFile attribute 'selecthiveql.row.count' indicates how many rows were selected. But you can file a jira addressing the issue found.

As a work around to fix this issue You can use PutDistributeCacheMap processor to keep all your attributes in cache server and fetch the attributes from cache server using FetchDistributeCacheMap processor.

Sample Flow Example:-

i'm using GenerateFlowFile processor and adding 3 attributes to the flowfile

attr1

56

attr2

67

attr3

89

ReplaceText Processor:-

Search Value

(?s)(^.*$)

Replacement Value

${allAttributes("attr1","attr2","attr3"):join("|")}

//i'm using allAttributes and keeping all the attributes with "|" pipe delimiter(output flowfile will be 1|2|3)
Maximum Buffer Size

1 MB //needs to change the size if the content is more than 1MB size.

Replacement Strategy

Always Replace

Evaluation Mode

Entire text

Use this link to evaluate multiple attributes.

UpdateAttribute:-

We are using this processor to change the filename of flowfile to UUID because We cannot not refer to use UUID as cache identifier reason is output from SelectHiveQL processor is having same filename but different UUID(i.e until selecthiveq processor flowfile having one uniqueid after selecthiveql processor different uuid).**

Add new property as

filename

${UUID()}

PutDistributeCache processor:-

Configure DistributedMapCacheServer,DistributedMapCacheClientService and enable them(you need to change cache number of entriesas per your needs,persistence directory if not mentioned then all the entries will be stored in memory).

Cache Entry Identifier

${filename}

Now we have changed the flowfile content and cached the output content with the filename.

SelectHiveQL processor:-

Feed success relation to SelectHiveQL processor once the processor outputs flowfile with content of the flowfile then feed the success relationship to

FetchDistributeCacheMap:-

Configs:-

Cache Entry Identifier

${filename:substringBefore('.')} //because based on output ff format we are going to have .avro/.csv extensions

Distributed Cache Service

DistributedMapCacheClientService

Put Cache Value In Attribute

cache_value //the cached content will be put in to this attribute instead putting into flowfile content

Max Length To Put In Attribute

256 //needs to change the value if max length is more than this value

Output:-

Flowfile will have attribute called cached.value then you can rebuild all your attributes by using getDelimitedField function

 ${cached.value:getDelimitedField(1, '|')} //will give attr1 field

Even without rebuilding all the attributes again by using above expression language you can directly pull the required attribute value and use them in your flow.
I have attached my sample flow.xml below, save and upload the xml to your instance and change the as per your needs.

selecthiveql-attributes-188338.xml

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