[postgis-tickets] [PostGIS] #4973: ST_AsMVT returns broken tiles when column name and JSONB key are the same

[PostGIS]

#4973: ST_AsMVT returns broken tiles when column name and JSONB key are the same
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  Reporter:  emreisikligil  |      Owner:  pramsey
      Type:  defect         |     Status:  new
  Priority:  critical       |  Milestone:  PostGIS 3.1.4
 Component:  postgis        |    Version:  3.1.x
Resolution:                 |   Keywords:  ST_AsMVT
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Comment (by Algunenano):

 Looks like we aren't controlling that a key doesn't get added twice, which
 can only happen when you use JSON / JSONB types.

 The spec is clear in saying that this is forbidden:

 {{{
 Feature attributes are encoded as pairs of integers in the tag field of a
 feature. The first integer in each pair represents the zero-based index of
 the key in the keys set of the layer to which the feature belongs. The
 second integer in each pair represents the zero-based index of the value
 in the values set of the layer to which the feature belongs. Every key
 index MUST be unique within that feature such that no other attribute pair
 within that feature has the same key index. A feature MUST have an even
 number of tag fields. A feature tag field MUST NOT contain a key index or
 value index greater than or equal to the number of elements in the layer's
 keys or values set, respectively.
 }}}


 I think that the simplest way to address this would be to keep only the
 first key-value pair and ignore any extra appearances of that key in that
 feature. If we went any other way we would need to remove the previously
 added value (only if it's unique) and that would be a pain.

 Note that this is likely to also happen if you have multiple JSONB columns
 with the same key, so it's not an issue of just prefering columns of jsonb
 values.

-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/4973#comment:1>
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