Add Tables.isrowtable for convenience. Fixes #134

src/Tables.jl

@@ -207,7 +207,27 @@ columnaccess(::Type{<:AbstractColumns}) = true
 columns(x::AbstractColumns) = x
 schema(x::AbstractColumns) = nothing
 
-# default definitions
+"""
+    Tables.isrowtable(x) => Bool
+
+For convenience, some table objects that are naturally "row oriented" can
+define `Tables.isrowtable(::Type{TableType}) = true` to simplify satisfying the
+Tables.jl interface. Requirements for defining `isrowtable` include:
+  * `Tables.rows(x) === x`, i.e. the table object itself is a `Row` iterator
+  * If the table object is mutable, it should support:
+    * `push!(x, row)`: allow pushing a single row onto table
+    * `append!(x, rows)`: allow appending set of rows onto table
+  * If table object is mutable and indexable, it should support:
+    * `x[i] = row`: allow replacing of a row with another row by index
+
+A table object that defines `Tables.isrowtable` will have definitions for
+`Tables.istable`, `Tables.rowaccess`, and `Tables.rows` automatically defined.
+"""
+function isrowtable end
+
+isrowtable(::T) where {T} = isrowtable(T)
+isrowtable(::Type{T}) where {T} = false
+
 """
     Tables.istable(x) => Bool
 
@@ -220,7 +240,7 @@ of knowing that the generator is a table.
 function istable end
 
 istable(x::T) where {T} = istable(T) || TableTraits.isiterabletable(x) === true
-istable(::Type{T}) where {T} = false
+istable(::Type{T}) where {T} = isrowtable(T)
 
 """
     Tables.rowaccess(x) => Bool
@@ -239,7 +259,7 @@ natural for them to *consume* instead of worrying about what and how the input p
 function rowaccess end
 
 rowaccess(x::T) where {T} = rowaccess(T)
-rowaccess(::Type{T}) where {T} = false
+rowaccess(::Type{T}) where {T} = isrowtable(T)
 
 """
     Tables.columnaccess(x) => Bool

src/fallbacks.jl

@@ -77,6 +77,7 @@ end
 
 # this is our generic Tables.rows fallback definition
 function rows(x::T) where {T}
+    isrowtable(x) && return x
     # because this method is being called, we know `x` didn't define it's own Tables.rows
     # first check if it supports column access, and if so, wrap it in a RowIterator
     if columnaccess(T)

test/runtests.jl

@@ -741,3 +741,24 @@ Tables.columnnames(r::Columns) = fieldnames(Columns)
     @test Tables.schema(col) === nothing
     @test isequal(Tables.columntable(col), ct)
 end
+
+struct IsRowTable
+    rows::Vector{NamedTuple}
+end
+
+Base.iterate(x::IsRowTable) = iterate(x.rows)
+Base.iterate(x::IsRowTable, st) = iterate(x.rows, st)
+Base.length(x::IsRowTable) = length(x.rows)
+
+Tables.isrowtable(::Type{IsRowTable}) = true
+
+@testset "Tables.isrowtable" begin
+
+    nt = (a=1, b=3.14, c="hey")
+    rt = IsRowTable([nt, nt, nt])
+    @test Tables.istable(rt)
+    @test Tables.rowaccess(rt)
+    @test Tables.rows(rt) === rt
+    @test Tables.columntable(rt) == Tables.columntable([nt, nt, nt])
+
+end