Add numeric decoder

CHANGELOG.md

@@ -1,6 +1,10 @@
 # Changelog
 
-## v4.0.0 - Unreleased
+## Unreleased
+
+- Added a `numeric_decoder` to decode numeric types coming from postgres.
+
+## v4.0.0 - 2025-07-07
 
 - Starting a pool no longer generates an atom, instead a name is taken as an
   argument.

src/pog.gleam

@@ -904,3 +904,7 @@ fn seconds_decoder() -> decode.Decoder(#(Int, Int)) {
   }
   decode.one_of(int, [float])
 }
+
+pub fn numeric_decoder() -> decode.Decoder(Float) {
+  decode.one_of(decode.float, [decode.int |> decode.map(int.to_float)])
+}

test/pog_test.gleam

@@ -333,6 +333,27 @@ pub fn float_test() {
   |> disconnect
 }
 
+pub fn numeric_test() {
+  let db =
+    start_default()
+    |> assert_roundtrip(0.0, "numeric", pog.float, pog.numeric_decoder())
+    |> assert_roundtrip(10.0, "numeric", pog.float, pog.numeric_decoder())
+    |> assert_roundtrip(1.1, "numeric", pog.float, pog.numeric_decoder())
+    |> assert_roundtrip(1.0, "numeric", pog.float, pog.numeric_decoder())
+
+  assert pog.query("select 1::numeric")
+    |> pog.returning(decode.at([0], pog.numeric_decoder()))
+    |> pog.execute(db.data)
+    == Ok(pog.Returned(count: 1, rows: [1.0]))
+
+  assert pog.query("select 0::numeric")
+    |> pog.returning(decode.at([0], pog.numeric_decoder()))
+    |> pog.execute(db.data)
+    == Ok(pog.Returned(count: 1, rows: [0.0]))
+
+  disconnect(db)
+}
+
 pub fn text_test() {
   start_default()
   |> assert_roundtrip("", "text", pog.text, decode.string)