I am trying to do pattern matching against a postgrex result, as such:
{:ok, %Postgrex.Result{rows: [[result]]}} = Postgrex.query!(:postgrex, "SELECT COUNT(1)
FROM pages
WHERE url = $1;", [url])
but I get
** (Mix) Could not start application dbhandler: DBHandler.Application.start(:normal, []) returned an error: shutdown: failed to start child: DBHandler
** (EXIT) an exception was raised:
** (MatchError) no match of right hand side value: %Postgrex.Result{command: :select, columns: ["count"], rows: [[1]], num_rows: 1, connection_id: 17022, messages: []}
(dbhandler 0.1.0) lib/dbhandler.ex:139: DBHandler.private_in_db?/1
(dbhandler 0.1.0) lib/dbhandler.ex:70: anonymous fn/1 in DBHandler.init/1
(elixir 1.17.3) lib/enum.ex:987: Enum."-each/2-lists^foreach/1-0-"/2
(dbhandler 0.1.0) lib/dbhandler.ex:69: DBHandler.init/1
(stdlib 4.3.1.6) gen_server.erl:851: :gen_server.init_it/2
(stdlib 4.3.1.6) gen_server.erl:814: :gen_server.init_it/6
(stdlib 4.3.1.6) proc_lib.erl:240: :proc_lib.init_p_do_apply/3
What I might be doing wrong is that I didn’t put all the elements of the map, but I don’t THINK I have to do that.
So, is there a way to do this that works, or do I have to find a way other than pattern matching?
Postgrex.query! raises a Postgrex.Error exception if anything goes wrong, so it returns an Postgrex.Result without an {:ok, ...} wrapper.
You could either remove the {:ok, ...} part on the left-hand side or switch the right-hand side to Postgrex.query (no !), depending on exactly what you want to happen if the query fails.
âžś sql git:(main) âś— iex -S mix
Erlang/OTP 27 [erts-15.2] [source] [64-bit] [smp:10:10] [ds:10:10:10] [async-threads:1] [jit]
Interactive Elixir (1.18.0) - press Ctrl+C to exit (type h() ENTER for help)
The database for SQL.Repo has already been created
iex(1)> import SQL
SQL
iex(2)> state = %{lock: [], politeness: []}
%{lock: [], politeness: []}
iex(3)> query = ~SQL[from pages] |> ~SQL[where url not in #{state.lock}] |> ~SQL[where host not in #{state.politeness}] |> ~SQL"select url"
select url from pages where url not in where host not in
iex(4)> state = %{lock: ["c", "d"], politeness: ["a", "b"]}
%{lock: ["c", "d"], politeness: ["a", "b"]}
iex(5)> query = ~SQL[from pages] |> ~SQL[where url not in #{state.lock}] |> ~SQL[where host not in #{state.politeness}] |> ~SQL"select url"
select url from pages where url not in 'c' 'd' where host not in 'c' 'd'
Could it be that you don’t import SQL or can you give me a better code example then the snippet?
Or could it be that there is something else interferring?
Actually, it was exactly that, I used use instead of import…
Well now I have another error but that’s from postgrex:
** (MatchError) no match of right hand side value: {:error, %Postgrex.Error{message: nil, postgres: %{code: :syntax_error, file: "scan.l", line: "1244", message: "syntax error at or near \"$0\"", pg_code: "42601", position: "40", routine: "scanner_yyerror", severity: "ERROR", unknown: "ERROR"}, connection_id: 18126, query: "select url from pages where url not in $0 where host not in $0"}}
