Allow any TableTraits source to satisfy the Tables interface (#45)

* Allow any TableTraits source to satisfy the Tables interface

* Remove Manifest

* Add tests for new TableTraits integration

Author: quinnj

Manifest.toml

@@ -5,4 +5,6 @@ version = "0.1.9"
 
 [deps]
 Requires = "ae029012-a4dd-5104-9daa-d747884805df"
+TableTraits = "3783bdb8-4a98-5b6b-af9a-565f29a5fe9c"
+IteratorInterfaceExtensions = "82899510-4779-5014-852e-03e436cf321d"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

Project.toml

@@ -2,6 +2,8 @@ module Tables
 
 using Requires
 
+using TableTraits, IteratorInterfaceExtensions
+
 export rowtable, columntable
 
 function __init__()
@@ -116,7 +118,8 @@ Obviously every table type is different, but via a combination of `Tables.rows`
 abstract type Table end
 
 # default definitions
-istable(x::T) where {T} = istable(T)
+istable(x::T) where {T} = istable(T) || TableTraits.isiterabletable(x) === true ||
+    TableTraits.isiterabletable(x) === missing
 istable(::Type{T}) where {T} = false
 rowaccess(x::T) where {T} = rowaccess(T)
 rowaccess(::Type{T}) where {T} = false

src/Tables.jl

@@ -59,6 +59,10 @@ function rows(x::T) where {T}
         cols = columns(x)
         return RowIterator(cols, rowcount(cols))
     else
+        it = TableTraits.isiterabletable(x)
+        if it === true || it === missing
+            return DataValueUnwrapper(IteratorInterfaceExtensions.getiterator(x))
+        end
         throw(ArgumentError("no default `Tables.rows` implementation for type: $T"))
     end
 end
@@ -146,7 +150,17 @@ end
     if rowaccess(T)
         r = rows(x)
         return buildcolumns(schema(r), r)
+    elseif TableTraits.supports_get_columns_copy_using_missing(x)
+        return TableTraits.get_columns_copy_using_missing(x)
     else
+        it = TableTraits.isiterabletable(x)
+        y = IteratorInterfaceExtensions.getiterator(x)
+        if it === true
+            return columns(DataValueUnwrapper(y))
+        elseif it === missing
+            # non-NamedTuple or EltypeUnknown
+            return buildcolumns(nothing, DataValueUnwrapper(y))
+        end
         throw(ArgumentError("no default `Tables.columns` implementation for type: $T"))
     end
 end

src/fallbacks.jl

@@ -1,4 +1,4 @@
-using Test, Tables
+using Test, Tables, TableTraits
 
 @testset "utils.jl" begin
 
@@ -223,6 +223,19 @@ end
     @test sortperm([a, b, c, d]) == [3, 1, 2, 4]
 end
 
+struct ColumnSource
+end
+
+TableTraits.supports_get_columns_copy_using_missing(::ColumnSource) = true
+
+function TableTraits.get_columns_copy_using_missing(x::ColumnSource)
+    return (a=[1,2,3], b=[4.,5.,6.], c=["A", "B", "C"])
+end
+
+let x=ColumnSource()
+    @test Tables.columns(x) == TableTraits.get_columns_copy_using_missing(x)
+end
+
 @static if :Query in Symbol.(Base.loaded_modules_array())
     rt = (a = Real[1, 2.0, 3], b = Union{Missing, Float64}[4.0, missing, 6.0], c = ["7", "8", "9"])
 
@@ -250,4 +263,4 @@ end
     rt = (a = Missing[missing, missing], b=[1,2])
     dv = Tables.datavaluerows(rt)
     @test eltype(dv) == NamedTuple{(:a, :b), Tuple{DataValue{Union{}}, Int}}
-end
+end