One question is to allow passing ... arguments to the DataFrame to csv
conversion functions while still retaining the chain-able argument in the
lass position; see https://github.com/JuliaLang/julia/issues/11722
On Saturday, June 27, 2015 at 10:19:35 AM UTC-4, Brandon Taylor wrote:
>
> Here is a simplified version of a DBI type scheme, almost entirely using
> convert function overloads. I temporarily have eval_foreign instead of
> eval, because I cannot figure out how to overload Base.eval successfully.
>
> cd("/home/haldane/Julia_package")
>
> using DataFrames
> using SQLite
> using Lazy
>
> import Base.convert
>
> type DataBaseTable
> conn::SQLiteDB
> name::String
> end
>
> type CsvFile
> file::String
> end
>
> function convert(::Type{DataBaseTable},
> conn::SQLiteDB,
> name::String,
> df::DataFrame)
> create(conn,
> name,
> df,
> @>> df names map(string) )
>
> DataBaseTable(conn, name)
> end
>
> function convert(::Type{SQLiteDB}, string::String)
> SQLiteDB(string)
> end
>
> function eval_foreign(db::SQLiteDB, code::String)
> query(db, code)
> end
>
> function convert(::Type{Dict}, conn::SQLiteDB)
> names = @as _ begin
> "select name from sqlite_master where type = 'table'"
> eval_foreign(conn, _)
> _.values[1]
> end
>
> [symbol(name) => DataBaseTable(conn, name) for name in names]
> end
>
> function convert(::Type{DataFrame}, dbt::DataBaseTable)
> answer = eval_foreign(dbt.conn, "select * from $(dbt.name)" )
> df = DataFrame(answer.values)
> @>> answer.colnames map(symbol) names!(df)
> end
>
> function convert(::Type{CsvFile}, name::String, df::DataFrame)
> writetable(name, df)
> CsvFile(name)
> end
>
> function convert(::Type{DataFrame}, file::String)
> readtable(file)
> end
>
> function convert(::Type{DataFrame}, cf = CsvFile)
> readtable(cf.file)
> end
>
> conn = @>> "my_database.db" convert(SQLiteDB)
>
> A = DataFrame(a = 1, b = 2)
> B = DataFrame(a = 1, b = 2)
>
> @>> A convert(DataBaseTable, conn, "A")
> @>> B convert(DataBaseTable, conn, "B")
>
> tables = @>> conn convert(Dict)
>
> A = @>> begin
> tables[:A] https://github.com/JuliaLang/julia/issues/11722
> convert(DataFrame)
> convert(CsvFile, "A.csv")
> convert(DataFrame)
> end
>
>
>
>
