Correct error writing struct

[jcunwin]

When using CSV.write on a array of structs, I want to override the column names of the struct in the CSV header.

using Dates
using CSV

struct StructType
    adate::Date
    astring::Union{String, Nothing}
    anumber::Union{Real, Nothing}
end

structtable = [StructType(Date("2021-12-01"), "string 1", 123.45), StructType(Date("2021-12-31"), "string 2", 456.78)]

io = IOBuffer()

CSV.write(io, structtable; header=["Date Column", "String Column", "Number Column"])

An exception occurs because write.jl tries to use the specified header value ("Date Column") to retrieve the struct's property value instead of the struct property name (:adate), resulting in an exception. E.g.:

CSV.write: Error During Test at /home/john/Code/investments/CSV.jl/test/write.jl:41
  Got exception outside of a @test
  type StructType has no field Date Column
  Stacktrace:
    [1] getproperty
      @ ./Base.jl:42 [inlined]
    [2] getcolumn(x::StructType, nm::Symbol)
      @ Tables ~/.julia/packages/Tables/M26tI/src/Tables.jl:102
    [3] getcolumn
      @ ~/.julia/packages/Tables/M26tI/src/tofromdatavalues.jl:74 [inlined]
    [4] eachcolumn
      @ ~/.julia/packages/Tables/M26tI/src/utils.jl:86 [inlined]
etc...

I.e. It tries something like:

getproperty(Symbol("Date Column"))

instead of something like:

getproperty(Symbol(:adate))

A fix is possible in write.jl in the write function. I.e. instead of using the header names to derive the schema:

# handle unknown schema case
function write(::Nothing, rows, file, opts;
        append::Bool=false,
        compress::Bool=false,
        header::Union{Bool, Vector}=String[],
        bufsize::Int=2^22
    )

#snip

    names = header isa Bool || isempty(header) ? propertynames(row) : header
    sch = Tables.Schema(names, nothing)    # <- Problem is here - wrongly using header values
    cols = length(names)

#snip

    return file
end

... use the data schema directly:

# handle unknown schema case
function write(::Nothing, rows, file, opts;
        append::Bool=false,
        compress::Bool=false,
        header::Union{Bool, Vector}=String[],
        bufsize::Int=2^22
    )

#snip

    names = header isa Bool || isempty(header) ? propertynames(row) : header
    sch = Tables.Schema(propertynames(row), nothing)   # <- fix is here - use property names
    cols = length(names)

#snip

    return file
end

I have created a fork with a code fix and a test case here:

https://github.com/jcunwin/CSV.jl

[codecov]

Codecov Report

Merging #961 (ac6d567) into main (482a187) will decrease coverage by 0.32%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #961      +/-   ##
==========================================
- Coverage   90.28%   89.95%   -0.33%     
==========================================
  Files           9        9              
  Lines        2306     2211      -95     
==========================================
- Hits         2082     1989      -93     
+ Misses        224      222       -2     

Impacted Files	Coverage Δ
src/write.jl	84.52% <100.00%> (ø)
src/file.jl	95.19% <0.00%> (-0.50%)	⬇️
src/utils.jl	85.98% <0.00%> (-0.43%)	⬇️
src/chunks.jl	91.30% <0.00%> (ø)
src/context.jl	88.81% <0.00%> (+0.16%)	⬆️
src/rows.jl	83.76% <0.00%> (+0.34%)	⬆️

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[quinnj]

Thanks @jcunwin for this!