Package com.bazaarvoice.jolt
Class CardinalityTransform
java.lang.Object
com.bazaarvoice.jolt.CardinalityTransform
- All Implemented Interfaces:
JoltTransform
,SpecDriven
,Transform
The CardinalityTransform changes the cardinality of input JSON data elements.
The impetus for the CardinalityTransform, was to deal with data sources that are inconsistent with
respect to the cardinality of their returned data.
For example, say you know that there will be a "photos" element in a document. If your underlying data
source is trying to be nice, it may adjust the "type" of the photos element, depending on how many
photos there actually are.
Single photo :
"photos" : { "url" : "pants.com/1.jpg" } // photos element is a "single" map entryOr multiple photos :
"photos" : [ { "url" : "pants.com/1.jpg" }, { "url" : "pants.com/2.jpg" } ]The Shiftr and Defaultr transforms can't handle that variability, so the CardinalityTransform was created to "fix" document, so that the rest of the transforms can _assume_ "photos" will be an Array. At a base level, a single Cardinality "command" maps data into a "ONE" or "MANY" state. The idea is that you can start with a copy your JSON input and modify it into a Cardinality spec by specifying a "cardinality" for each piece of data that you care about changing in the output. Input data that are not called out in the spec will remain in the output unchanged. For example, given this simple input JSON :
{ "review" : { "rating" : [ 5, 4 ] } }A simple Cardinality spec could be constructed by specifying that the "rating" should be a single value:
{ "review" : { "rating" : "ONE" } }would product the following output JSON :
{ "review" : { "rating" : 5 } }In this case, we turn the array "[ 5, 4 ]" into a single value by pulling the first index of the array. Hence, the output has "rating : 5". Valid Cardinality Values (RHS : right hand side) 'ONE' If the input value is a List, grab the first element in that list, and set it as the data for that element For all other input value types, no-op. 'MANY' If the input is not a List, make a list and set the first element to be the input value. If the input is "null", make it be an empty list. If the input is a list, no-op Cardinality Wildcards As shown above, Cardinality specs can be entirely made up of literal string values, but wildcards similar to some of those used by Shiftr can be used. '*' Wildcard Valid only on the LHS ( input JSON keys ) side of a Cardinality Spec Unlike shiftr, the '*' wildcard can only be used by itself. It can be used achieve a for/each manner of processing input. Let's say we have the following input :
{ "photosArray" : [ { "url" : [ "http://pants.com/123-normal.jpg", "http://pants.com/123-thumbnail.jpg" ], "caption" : "Nice pants" }, { "url" : [ "http://pants.com/123-thumbnail.jpg", "http://pants.com/123-normal.jpg" ], "caption" : "Nice pants" } ] }And we'd like a spec that says "for each item 'url', covert to ONE" :
{ "photosArray" : { "*" : { // for each item in the array "url" : "ONE" // url should be singular } } }Which would yield the following output :
{ "photosArray" : [ { "url" : "http://pants.com/123-normal.jpg", "caption" : "Nice pants" }, { "url" : "http://pants.com/123-thumbnail.jpg", "caption" : "Nice pants" } ] }'@' Wildcard Valid only on the LHS of the spec. This wildcard should be used when content nested within modified content needs to be modified as well. Let's say we have the following input:
{ "views" : [ { "count" : 1024 }, { "count" : 2048 } ], }The following spec would convert "views" to a ONE and "count" to a MANY :
{ "views" : { "@" : "ONE", "count" : "MANY" } }Yielding the following output:
{ "views" : { "count" : [ 1024 ] } }Cardinality Logic Table
INPUT CARDINALITY OUTPUT NOTE String ONE String no-op Number ONE Number no-op Boolean ONE Map no-op Map ONE Map no-op List ONE [0] use whatever the first item in the list was String MANY List make the input String, be [0] in a new list Number MANY List make the input Number, be [0] in a new list Boolean MANY List make the input Boolean, be [0] in a new list Map MANY List make the input Map, be [0] in a new list List MANY List no-op
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected static final String
private final CardinalityCompositeSpec
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Constructor Summary
ConstructorsConstructorDescriptionCardinalityTransform
(Object spec) Initialize a Cardinality transform with a CardinalityCompositeSpec. -
Method Summary
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Field Details
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ROOT_KEY
- See Also:
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rootSpec
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Constructor Details
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CardinalityTransform
Initialize a Cardinality transform with a CardinalityCompositeSpec.- Throws:
SpecException
- for a malformed spec
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Method Details
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transform
Applies the Cardinality transform.- Specified by:
transform
in interfaceTransform
- Parameters:
input
- the JSON object to transform- Returns:
- the output object with data shifted to it
- Throws:
TransformException
- for a malformed spec or if there are issues during the transform
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