Add DataAPI metadata passthrough to apply (#211)

* Add DataAPI metadata passthrough

* Don't need input metadata for CRS/geometrycolumn

Project.toml

@@ -5,6 +5,7 @@ version = "0.1.11"
 
 [deps]
 CoordinateTransformations = "150eb455-5306-5404-9cee-2592286d6298"
+DataAPI = "9a962f9c-6df0-11e9-0e5d-c546b8b5ee8a"
 DelaunayTriangulation = "927a84f5-c5f4-47a5-9785-b46e178433df"
 ExactPredicates = "429591f6-91af-11e9-00e2-59fbe8cec110"
 GeoInterface = "cf35fbd7-0cd7-5166-be24-54bfbe79505f"

src/GeometryOps.jl

@@ -6,7 +6,7 @@ using GeoInterface
 using GeometryBasics
 using LinearAlgebra, Statistics
 
-import Tables
+import Tables, DataAPI
 import GeometryBasics.StaticArrays
 import DelaunayTriangulation # for convex hull and triangulation
 import ExactPredicates

src/primitives.jl

@@ -202,12 +202,47 @@ function _apply_table(f::F, target, iterable::IterableType; threaded, kw...) whe
     new_names = filter(Base.Fix1(!==, geometry_column), old_schema.names)
     # and try to rebuild the same table as the best type - either the original type of `iterable`,
     # or a named tuple which is the default fallback.
-    return Tables.materializer(iterable)(
+    result = Tables.materializer(iterable)(
         merge(
             NamedTuple{(geometry_column,), Base.Tuple{typeof(new_geometry)}}((new_geometry,)),
             NamedTuple(Iterators.map(_get_col_pair, new_names))
         )
     )
+    # Finally, we ensure that metadata is propagated correctly.
+    # This can only happen if the original table supports metadata reads,
+    # and the result supports metadata writes.
+    if DataAPI.metadatasupport(typeof(result)).write
+        # Copy over all metadata from the original table to the new table, 
+        # if the original table supports metadata reading.
+        if DataAPI.metadatasupport(IterableType).read
+            for (key, (value, style)) in DataAPI.metadata(iterable; style = true)
+                # Default styles are not preserved on data transformation, so we must skip them!
+                style == :default && continue
+                # We assume that any other style is preserved.
+                DataAPI.metadata!(result, key, value; style)
+            end
+        end
+        # We don't usually care about the original table's metadata for GEOINTERFACE namespaced
+        # keys, so we should set the crs and geometrycolumns metadata if they are present.
+        # Ensure that `GEOINTERFACE:geometrycolumns` and `GEOINTERFACE:crs` are set!
+        mdk = DataAPI.metadatakeys(result)
+        # If the user has asked for geometry columns to persist, they would be here,
+        # so we don't need to set them.
+        if !("GEOINTERFACE:geometrycolumns" in mdk)
+            # If the geometry columns are not already set, we need to set them.
+            DataAPI.metadata!(result, "GEOINTERFACE:geometrycolumns", (geometry_column,); style = :default)
+        end
+        # Force reset CRS always, since you can pass `crs` to `apply`.
+        new_crs = if haskey(kw, :crs)
+            kw[:crs]
+        else
+            GI.crs(iterable) # this will automatically check `GEOINTERFACE:crs` unless the type has a specialized implementation.
+        end
+
+        DataAPI.metadata!(result, "GEOINTERFACE:crs", new_crs; style = :default)
+    end
+
+    return result
 end
 
 # Rewrap all FeatureCollectionTrait feature collections as GI.FeatureCollection

test/primitives.jl

@@ -2,12 +2,13 @@ using Test
 
 import ArchGDAL as AG
 import GeometryBasics as GB 
+import GeoFormatTypes as GFT
 import GeometryOps as GO 
 import GeoInterface as GI
 import LibGEOS as LG
 import Proj
 import Shapefile
-import DataFrames
+import DataFrames, Tables, DataAPI
 using Downloads: download
 using ..TestHelpers
 
@@ -54,7 +55,9 @@ poly = GI.Polygon([lr1, lr2])
 
             @testset "DataFrames" begin
                 countries_df = DataFrames.DataFrame(countries_table)
-                centroid_df = GO.apply(GO.centroid, GO.TraitTarget(GI.PolygonTrait(), GI.MultiPolygonTrait()), countries_df);
+                GO.DataAPI.metadata!(countries_df, "note metadata", "note metadata value"; style = :note)
+                GO.DataAPI.metadata!(countries_df, "default metadata", "default metadata value"; style = :default)
+                centroid_df = GO.apply(GO.centroid, GO.TraitTarget(GI.PolygonTrait(), GI.MultiPolygonTrait()), countries_df; crs = GFT.EPSG(3031));
                 @test centroid_df isa DataFrames.DataFrame
                 centroid_geometry = centroid_df.geometry
                 # Test that the centroids are correct
@@ -64,6 +67,12 @@ poly = GI.Polygon([lr1, lr2])
                         @test all(missing_or_equal.(centroid_df[!, column], countries_df[!, column]))
                     end
                 end
+                @testset "Metadata preservation (or not)" begin
+                    @test DataAPI.metadata(centroid_df, "note metadata") == "note metadata value"
+                    @test !("default metadata" in DataAPI.metadatakeys(centroid_df))
+                    @test DataAPI.metadata(centroid_df, "GEOINTERFACE:geometrycolumns") == (:geometry,)
+                    @test DataAPI.metadata(centroid_df, "GEOINTERFACE:crs") == GFT.EPSG(3031)
+                end
             end
         end
         end