laurentgo commented on code in PR #13879:
URL: https://github.com/apache/iceberg/pull/13879#discussion_r2467815935
##########
open-api/rest-catalog-open-api.yaml:
##########
@@ -3260,6 +3260,71 @@ components:
additionalProperties:
type: string
+ ReadRestrictions:
+ type: object
+ description: >
+ Read restrictions for a table, including projection and row filter
expressions, according to the current schema.
+
+ A client MUST enforce the restrictions defined in this object when
reading data
+ from the table.
+
+ These restrictions apply only to the authenticated principal, user,
or account
+ associated with the client. They MUST NOT be interpreted as global
policy and
+ MUST NOT be applied beyond the entity identified by the
Authentication header
+ (or other applicable authentication mechanism).
+ properties:
+ required-projection:
+ description: >
+ A list of projections that MUST be applied prior to any
query-specified
+ projections.
+ If the required-projection property is absent or empty, no
mandatory projection applies,
+ and a reader MAY project any subset of columns of the table,
including all columns.
+
+ 1. A reader MUST project only columns listed in the
required-projection.
+ - If a listed column has a transform, the reader MUST apply it
and replace
+ all references to the underlying column with the transformed
value
+ (for example, truncate(4, cc) MUST be projected as truncate(4,
cc) AS cc,
+ and all references to cc during query evaluation MUST resolve
to this alias).
+ - If a listed column has no transform, the reader MUST read it
as-is.
+ - Columns not listed in the required-projection MUST NOT be read.
+
+ 2. A column MUST appear at most once in the required-projection.
+
+ 3. A projection entry MUST reference either the column itself or
exactly one
+ transformed version of the column, but not both.
+
+ 4. Multiple transformed versions of the same column (e.g.,
truncate(5, col)
+ and truncate(3, col)) MUST NOT appear in the required-projection.
+
+ 5. If a projection entry includes a transform that the reader
cannot evaluate,
+ the reader MUST fail rather than ignore the transform.
+
+ 6. An identity transform is equivalent to projecting the column
directly.
+ A reader MAY represent it in either form.
+
+ 7. The data type of the projected column MUST match the data type
defined for the transform result.
+
+ type: array
+ items:
+ $ref: '#/components/schemas/Term'
Review Comment:
I'm not sure about the link with the other PR as I thought its scope was to
augment the expression API.
What I'm suggesting here instead is that `required-projections` to be a
array of `Projection` objects instead of `Term`, with `Projection` being a
object with the following fields `column-id` (int), `column-name` (string),
`projection` (Term).
I saw a comment suggesting to use a map instead to associate column names to
projection, which is an option as well. But I believe my suggestion to be okay
as well and allow for future extensibility (in case we want to convey more data
in the future like the type of expression).
Having an explicit mapping allows to rewrite some of those rules, namely
that a column id/column name should only appear at most once in the whole array
while some other rules would become unnecessary.
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