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https://issues.apache.org/jira/browse/CALCITE-6832?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17926967#comment-17926967
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Stamatis Zampetakis commented on CALCITE-6832:
----------------------------------------------
It seems that the redundancy started from
[ca9f0053611f54d92852a5c85e369a98bd3f91e7|https://github.com/apache/calcite/commit/ca9f0053611f54d92852a5c85e369a98bd3f91e7]
which landed in 1.27.0 release.
> Redundant fields/nullable entries in STRUCT serialization to JSON
> -----------------------------------------------------------------
>
> Key: CALCITE-6832
> URL: https://issues.apache.org/jira/browse/CALCITE-6832
> Project: Calcite
> Issue Type: Bug
> Affects Versions: 1.38.0
> Reporter: Stamatis Zampetakis
> Assignee: Stamatis Zampetakis
> Priority: Major
> Fix For: 1.39.0
>
>
> The JSON serialization of a {{RelDatatypeField}} of type STRUCT contains
> redundant fields and nullable entries along with unnecessary nesting.
> Consider for example, a field "address" of type STRUCT composed from the
> following fields.
> {code:java}
> RelDataType type = typeFactory.builder()
> .add("street", SqlTypeName.VARCHAR, 50)
> .add("number", SqlTypeName.INTEGER)
> .add("building", SqlTypeName.VARCHAR, 20).nullable(true)
> .build();
> RelDataTypeField address =
> new RelDataTypeFieldImpl("address", 0, type);
> {code}
> At the moment, the JSON serialization for the field "address" is shown below.
> {code:json}
> {
> "fields": {
> "fields": [
> {
> "type": "VARCHAR",
> "nullable": false,
> "precision": 50,
> "name": "street"
> },
> {
> "type": "INTEGER",
> "nullable": false,
> "name": "number"
> },
> {
> "type": "VARCHAR",
> "nullable": true,
> "precision": 20,
> "name": "building"
> }
> ],
> "nullable": false
> },
> "nullable": false,
> "name": "address"
> }
> {code}
> Note that the "fields" key appears twice and there is an unnecessary wrapping
> of a JSON array (inner "fields") inside a JSON object (outer "fields"). The
> outer "fields" object cannot have more entries so it doesn't offer anything.
> Moreover, observe that there are two {{"nullable":false}} entries and both
> reflect the nullability of the "address" field.
> The redundancy leads to wasted space and more convoluted representation that
> is hard to follow especially when there are nested STRUCTS.
> The same information could be represented using the following JSON
> serialization:
> {code:json}
> {
> "fields": [
> {
> "type": "VARCHAR",
> "nullable": false,
> "precision": 50,
> "name": "street"
> },
> {
> "type": "INTEGER",
> "nullable": false,
> "name": "number"
> },
> {
> "type": "VARCHAR",
> "nullable": true,
> "precision": 20,
> "name": "building"
> }
> ],
> "nullable": false,
> "name": "address"
> }
> {code}
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