Irmin Store . Fetch all the values from the store

Learning
1

Hi,
I am trying out the example given fo irmin Store setup.

open Lwt.Infix

(* Irmin store with string contents *)
module Store = Irmin_unix.Git.FS.KV(Irmin.Contents.String)

(* Database configuration *)
let config = Irmin_git.config ~bare:true "/tmp/irmin/test"

(* Commit author *)
let author = "Example <example@example.com>"

(* Commit information *)
let info fmt = Irmin_unix.info ~author fmt

let main =
    (* Open the repo *)
    Store.Repo.v config >>=

    (* Load the master branch *)
    Store.master >>= fun t ->

    (* Set key "foo/bar" to "testing 123" *)
    Store.set t ~info:(info "Updating foo/bar") ["foo"; "bar"; key] "testing 123" >>= fun () ->

    (* Get key "foo/bar" and print it to stdout *)
    Store.get t ["foo"; "bar"] >|= fun x ->
    Printf.printf "foo/bar => '%s'\n" x

(* Run the program *)
let () = Lwt_main.run main

If the key and the value differs every time, I want to know if there is any way if I can fetch all the key value pairs stored in the path foo/bar

1 Like
2

This is possible via Store.get_tree. Once you have a tree, you can find the keys of its children with Store.Tree.list and get the children themselves with Store.Tree.get.

Something like:

(** Get the bindings in the tree at [root] *)
let bindings store root =
  Store.get_tree store root >>= fun tree ->
  Store.Tree.list tree >>= fun children ->

  (* Discard subtrees from the list *)
  List.filter_map (function 
     | (key, `Contents) -> Some key 
     | (_, `Node) -> None)) children

  (* Get remaining K/V pairs *)
  |> Lwt_list.map_s (fun k -> Store.Tree.get k >|= fun v -> (k, v))

Generally, if you want to do anything more complicated than getting/setting individual contents in the store, you should be using the Tree API.

3

Hi @CraigFe I am getting the below mentioned error.

18 |   Store.Tree.list tree >>= fun children ->
       ^^^^^^^^^^^^^^^^^^^^
Error: This expression has type
         Store.key -> (string * [ `Contents | `Node ]) list Lwt.t
       but an expression was expected of type 'a Lwt.t
4

Looks like you need to pass the empty key there to mean “get the bindings at the root of this tree”.

Store.Tree.list tree []
5

@CraigFe

program:
open Lwt.Infix

(* Irmin store with string contents *)
module Store = Irmin_unix.Git.FS.KV(Irmin.Contents.String)

(* Database configuration *)
let config = Irmin_git.config ~bare:true "/tmp/irmin/test"

(* Commit author *)
let author = "Example <example@example.com>"

(* Commit information *)
let info fmt = Irmin_unix.info ~author fmt

(** Get the bindings in the tree at [root] *)
let bindings store root =
  Store.get_tree store root >>= fun tree ->
  Store.Tree.list tree [] |> fun children ->
  List.filter_map (function 
     | (key, `Contents) -> Some key 
     | (_, `Node) -> None) children

  (* Get remaining K/V pairs *)
  |> Lwt_list.map_s (fun k -> Store.Tree.get k >|= fun v -> (k, v)) |>
    Lwt.return

    
    

let setter ()=
    (* Open the repo *)
    Store.Repo.v config >>=

    (* Load the master branch *)
    Store.master >>= fun t ->

    (* Set key "foo/bar" to "testing 123" *)
    Store.set t ~info:(info "Updating foo/bar") ["foo"; "bar"] "testing 123" >>= fun () ->
    
    print_endine "ss";
    let xyzz = bindings t ["foo"] in
    print_endline xyzz;
    ()





(* Run the program *)
let () = setter ()

Error:

File "unikernel.ml", line 21, characters 27-35:
21 |      | (_, `Node) -> None) children
                                ^^^^^^^^
Error: This expression has type (string * [ `Contents | `Node ]) list Lwt.t
       but an expression was expected of type
         ('a * [< `Contents | `Node ]) list
6

You need to bind the result of Store.Tree.list as I did in my original example, otherwise you’re trying to list map over a thread.

I suggest reading one of the several Lwt tutorials that exist out there if you’re unused to this sort of programming.

7

Thanks . I fixed the previous issue. Sorry for bothering you again but I am getting another error.

File "unikernel.ml", line 35, characters 30-46:
35 |   |> Lwt_list.map_s (fun k -> Store.Tree.get k >|= fun v -> (k, v))
                                   ^^^^^^^^^^^^^^^^
Error: This expression has type Store.key -> string Lwt.t
       but an expression was expected of type 'a Lwt.t
8

Oops, you’ll need to pass the tree there again… (Otherwise, what tree are you getting from?)

Store.Tree.get tree k
9

Still doesn’t work.

code:

let bindings store root =
  Store.get_tree store root >>= fun tree ->
  Store.Tree.list tree [] >>= fun children ->

  (* Discard subtrees from the list *)
  List.filter_map (function 
     | (key, `Contents) -> Some key 
     | (_, `Node) -> None) children

  (* Get remaining K/V pairs *)
  |> Lwt_list.map_s (fun k -> Store.Tree.get tree k >|= fun v -> (k, v))

Error:

File "unikernel.ml", line 35, characters 5-72:
35 |   |> Lwt_list.map_s (fun k -> Store.Tree.get tree k >|= fun v -> (k, v))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: This expression has type
         Store.key list -> (Store.key * string) list Lwt.t
       but an expression was expected of type string list -> 'a
       Type Store.key = string list is not compatible with type string
10 
Store.Tree.get tree [ k ]

since get takes a path and not a step.

I think you may have taken my hastily-typed sketch of an answer more literally than was intended :wink: I encourage you to read the documentation for these functions and talk to the typechecker until the two of you reach some sort of agreement :slightly_smiling_face: If you find the documentation lacking, suggestions are welcome.

11

ok. I am new to both OCaml and Irmin. After the example in the readme file, it is a little bit confusing to start with the documentation. More examples with comments would be helpful. But this discussion forum is helpful. Thank you @CraigFe

1 Like