F＃从CSV生成SQL

Question

I have recently been learning F# and functional programming. One application I have found very useful is generating SQL inserts for a data load from a CSV (or excel table) with some associated ID's.

The following code is my result, which I believe I will find very handy in the future. I thought others could also benefit from this and I welcome suggestions and other scripts which people have found invaluable in their collection:

// Returns some dataload SQL for area mapping.
open System
open System.IO

// Read and split CSV into lists
let map_ngo_area = File.ReadAllLines(@"P:\MY_TABLE.csv") 
                        |> Array.to_list
                        |> List.map(fun x -> (x.Split([|','|]) 
                                                |> Array.map(fun y -> y.Trim())) 
                                                |> Array.to_list)

// Output Formatting function
let format_sql_record = "INSERT INTO MyTable
     (ID, REF1_ID, REF2_ID, CreatedUser, CreatedDateTime, LastModifiedUser, LastModifiedDateTime)
     VALUES
     ( {0}, {1}, {2}, 'system', getDate(), 'system', getDate() )"

 // Generate the SQL for the given list.  
let generate_sql list = list |> List.mapi(fun index row -> 
                                            match row with
                                                | [ngo_id; area_id] -> String.Format(format_sql_record, ((int index)+1), ngo_id, area_id) |> printfn "%s"
                                                | _ -> printfn "")

// Main Execution
map_ngo_area |> generate_sql |> ignore

// End of program, pause to view console output.
System.Console.ReadKey() |> ignore

Any suggestions on improving my F# code or process? Comments also welcome, as I am fairly new at this paradigm and shifting thinking is not as forthcoming as I expected.

Thanks :)

Answer 1

Here are a few suggestions:

• Don't use List.mapi with functions that return unit , since there's not much you can do with the resulting unit list . You should use List.iteri instead, which will allow you to omit the |> ignore at the end of your main execution section.
• Going further, rather than having generate_sql print the generated lines one at a time, it might be better to generate a list of strings instead. Note that in this case, you would go back to using List.mapi since the function that you apply would return a result for each line.
• Use F#'s print formatting rather than String.Format . For instance rather than having format_sql_record be a string, have it be a function of type int->string->string->string : let format_sql_record = sprintf "INSERT INTO ... VALUES (%i, %s, %s, ...)"
• Depending on the version of F# that you're using, you should probably be using the renamed function Array.toList instead of Array.to_list , since that's the name that will be used in the final release of F#.

Answer 2

You can use pattern matching on arrays too:

let map_ngo_area = File.ReadAllLines(@"P:\MY_TABLE.csv") 
                    |> Array.to_list
                    |> List.map(fun x -> (x.Split([|','|]) 
                                            |> Array.map(fun y -> y.Trim())) 

let generate_sql list = list |> List.mapi(fun index row -> 
                                            match row with
                                            | [| ngo_id; area_id |] -> printfn ...
                                            | _ -> printfn "")