Dapper dot net query in F#

Question

I'm trying to use Dapper dot net in F# to perform a simple SQLite query. Dapper returns a collection of dynamic objects: using them in C# is straightforward, but from what I understood F# has no dynamic property lookup implementation out-of-the-box.

This is working but I suppose there are better ways to do this without resorting to reflection:

let (?) x prop =
    let flags = BindingFlags.GetProperty ||| BindingFlags.InvokeMethod
    x.GetType().InvokeMember(prop, flags, null, x, [||])

let doQuery () =
    //...
    let conn = new SQLiteConnection (connString)
    conn.Open ()

    conn.Query("select first_name from customers")
        |> Seq.map (fun c -> c ? first_name)
        |> List.ofSeq

What is the best way to implement the ? operator in this case?

It seems that this thread answers your question: http://stackoverflow.com/questions/6150087/f-dynamic-object-access — pad, Feb 20 '12 at 16:42
@pad Good answer. You should have added your response as an answer so I could upvote it :-) — Onorio Catenacci, Feb 20 '12 at 16:47
@OnorioCatenacci: I add it as an answer, not sure that it is worth an answer:). — pad, Feb 20 '12 at 17:00
Nit: use `c?first_name` (no spaces) to be idiomatic. `?` is like `.` here. — Brian, Feb 20 '12 at 17:09
Not a solution, but have you considered using FsSql (https://github.com/mausch/FsSql) instead? It's written specifically for F#. — Mauricio Scheffer, Feb 20 '12 at 17:26
I am accessing an existing db so I have no choice, but I'll keep FsSql and SOMA in mind for future needs! — Francesco De Vittori, Feb 23 '12 at 21:19
@FrancescoDeVittori : FsSql doesn't need a specific database schema, the main point of it is simply making ADO.NET more palatable from F#. — Mauricio Scheffer, Feb 24 '12 at 15:36
@Mauricio Scheffer: oh sorry hadn't realized that. Switching to FsSql immediately! — Francesco De Vittori, Feb 26 '12 at 07:58

score 7 · Accepted Answer · edited May 23 '17 at 10:29

7

This thread consists of several solutions for your problem. Especially, FSharp.Interop.Dynamic is available on NuGet and ready to use.

edited May 23 '17 at 10:29

Community

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answered Feb 20 '12 at 16:59

pad

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I was hoping there was an easier way (or without an external library). I suppose great power/great responsibility etc... :-) – Francesco De Vittori Feb 23 '12 at 21:20

score 3 · Answer 2 · answered May 05 '20 at 07:40

When using Dapper with F#, you can specify your query parameters using F# Anonymous Records and map the results directly to an F# Record, like so:

[<CLIMutable>]
type CustomerDto = 
    {
        FirstName: string
    }

let selectSql = "select first_name as FirstName from customers where first_name = @firstName"

conn.Query<CustomerDto>(selectSql, {|firstName = "Francesco"|})

Note that F# Anonymous Records were introduced in F# 4.6.

Dapper dot net query in F#

2 Answers2