[WIP] Add a Tables.jl extension for FeatureCollection and Feature

Project.toml

@@ -7,10 +7,17 @@ version = "1.3.6"
 Extents = "411431e0-e8b7-467b-b5e0-f676ba4f2910"
 GeoFormatTypes = "68eda718-8dee-11e9-39e7-89f7f65f511f"
 
+[weakdeps]
+Tables = "bd369af6-aec1-5ad0-b16a-f7cc5008161c"
+
+[extensions]
+GeoInterfaceTablesExt = "Tables"
+
 [compat]
 Extents = "0.1.1"
 GeoFormatTypes = "0.4"
-julia = "1"
+Tables = "1"
+julia = "1.9"
 
 [extras]
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"

ext/GeoInterfaceTablesExt.jl

@@ -0,0 +1,129 @@
+module GeoInterfaceTablesExt
+
+using GeoInterface
+using GeoInterface.Wrappers
+using Tables
+
+# This module is meant to extend the Tables.jl interface to features and feature collections, such that they can be used with Tables.jl.
+# This enables the use of the Tables.jl ecosystem with GeoInterface wrapper geometries.
+
+# First, define the Tables interface
+
+Tables.istable(::Type{<: Wrappers.FeatureCollection}) = true
+Tables.isrowtable(::Type{<: Wrappers.FeatureCollection}) = true
+Tables.rowaccess(::Type{<: Wrappers.FeatureCollection}) = true
+Tables.rows(fc::Wrappers.FeatureCollection{P, C, E}) where {P <: Union{AbstractArray{<: Wrappers.Feature}, Tuple{Vararg{<: Wrappers.Feature}}}, C, E} = GeoInterface.getfeature(fc)
+Tables.rows(fc::Wrappers.FeatureCollection) = Iterators.map(Wrappers.Feature, GeoInterface.getfeature(fc))
+Tables.schema(fc::Wrappers.FeatureCollection) = property_schema(GeoInterface.getfeature(fc))
+
+# Define the row access interface for feature wrappers
+function Tables.getcolumn(row::Wrappers.Feature, i::Int)
+    if i == 1
+        return GeoInterface.geometry(row)
+    else
+        return GeoInterface.properties(row)[i-1]
+    end
+end
+Tables.getcolumn(row::Wrappers.Feature, nm::Symbol) = nm === :geometry ? GeoInterface.geometry(row) : Tables.getcolumn(GeoInterface.properties(row), nm)
+Tables.columnnames(row::Wrappers.Feature) = (:geometry, propertynames(GeoInterface.properties(row))...)
+
+# Copied from GeoJSON.jl
+# Credit to [Rafael Schouten](@rafaqz)
+# Adapted from JSONTables.jl jsontable method
+# We cannot simply use their method as we have concrete types and need the key/value pairs
+# of the properties field, rather than the main object
+# TODO: Is `missT` required?
+# TODO: The `getfield` is probably required once
+missT(::Type{Nothing}) = Missing
+missT(::Type{T}) where {T} = T
+
+function property_schema(features)
+    # Otherwise find the shared names
+    names = Set{Symbol}()
+    types = Dict{Symbol,Type}()
+    for feature in features
+        props = GeoInterface.properties(feature)
+        isnothing(props) && continue
+        if isempty(names)
+            for k in keys(props)
+                k === :geometry && continue
+                push!(names, k)
+                types[k] = missT(typeof(props[k]))
+            end
+            push!(names, :geometry)
+            types[:geometry] = missT(typeof(GeoInterface.geometry(feature)))
+        else
+            for nm in names
+                T = types[nm]
+                if haskey(props, nm)
+                    v = props[nm]
+                    if !(missT(typeof(v)) <: T)
+                        types[nm] = Union{T,missT(typeof(v))}
+                    end
+                elseif hasfield(typeof(feature), nm)
+                    v = getfield(feature, nm)
+                    if !(missT(typeof(v)) <: T)
+                        types[nm] = Union{T,missT(typeof(v))}
+                    end
+                elseif !(T isa Union && T.a === Missing)
+                    types[nm] = Union{Missing,types[nm]}
+                end
+            end
+            for (k, v) in pairs(props)
+                k === :geometry && continue
+                if !(k in names)
+                    push!(names, k)
+                    types[k] = Union{Missing,missT(typeof(v))}
+                end
+            end
+        end
+    end
+    return collect(names), types
+end
+
+
+
+# Finally, define the metadata interface.  FeatureCollection wrappers have no metadata, so we simply specify geometry columns and CRS.
+
+Tables.DataAPI.metadatasupport(::Type{<: Wrappers.FeatureCollection}) = (; read = true, write = false)
+Tables.DataAPI.metadatakeys(::Wrappers.FeatureCollection) = ("GEOINTERFACE:geometrycolumns", "GEOINTERFACE:crs")
+function Tables.DataAPI.metadata(fc::Wrappers.FeatureCollection, key::AbstractString; style = false)
+    result = if key == "GEOINTERFACE:geometrycolumns"
+        (:geometry,)
+    elseif key == "GEOINTERFACE:crs"
+        if isnothing(GeoInterface.crs(fc))
+            nothing
+            # or
+            #=
+            GeoFormatTypes.ESRIWellKnownText(
+                """
+                ENGCRS["Undefined Cartesian SRS with unknown unit",
+                    EDATUM["Unknown engineering datum"],
+                    CS[Cartesian,2],
+                    AXIS["X",unspecified,
+                        ORDER[1],
+                        LENGTHUNIT["unknown",0]],
+                    AXIS["Y",unspecified,
+                        ORDER[2],
+                        LENGTHUNIT["unknown",0]]]
+                """
+            )
+            =#
+        else
+            GeoInterface.crs(fc)
+        end
+    else
+        throw(KeyError(key))
+    end
+
+    if style
+        return (result, :note)
+    else
+        return result
+    end
+end
+
+
+
+
+end # module