Use the JSON encoders for XLSX objects with no encoders

src/metabase/api/dataset.clj

@@ -19,7 +19,8 @@
             [metabase.query-processor.util :as qputil]
             [metabase.util.schema :as su]
             [schema.core :as s])
-  (:import [java.io ByteArrayInputStream ByteArrayOutputStream]))
+  (:import [java.io ByteArrayInputStream ByteArrayOutputStream]
+           org.apache.poi.ss.usermodel.Cell))
 
 ;;; ------------------------------------------------------------ Constants ------------------------------------------------------------
 
@@ -65,18 +66,30 @@
 
 ;;; ------------------------------------------------------------ Downloading Query Results in Other Formats ------------------------------------------------------------
 
-(defn- export-to-csv [columns rows]
-  (with-out-str
-    ;; turn keywords into strings, otherwise we get colons in our output
-    (csv/write-csv *out* (into [(mapv name columns)] rows))))
+;; add a generic implementation for the method that writes values to XLSX cells that just piggybacks off the implementations
+;; we've already defined for encoding things as JSON. These implementations live in `metabase.middleware`.
+(defmethod spreadsheet/set-cell! Object [^Cell cell, value]
+  (when (= (.getCellType cell) Cell/CELL_TYPE_FORMULA)
+    (.setCellType cell Cell/CELL_TYPE_STRING))
+  ;; stick the object in a JSON map and encode it, which will force conversion to a string. Then unparse that JSON and use the resulting value
+  ;; as the cell's new String value.
+  ;; There might be some more efficient way of doing this but I'm not sure what it is.
+  (.setCellValue cell (str (-> (json/generate-string {:v value})
+                               (json/parse-string keyword)
+                               :v))))
 
 (defn- export-to-xlsx [columns rows]
-  (let [wb  (spreadsheet/create-workbook "Query result" (conj rows (mapv name columns)))
+  (let [wb  (spreadsheet/create-workbook "Query result" (cons (mapv name columns) rows))
         ;; note: byte array streams don't need to be closed
         out (ByteArrayOutputStream.)]
     (spreadsheet/save-workbook! out wb)
     (ByteArrayInputStream. (.toByteArray out))))
 
+(defn- export-to-csv [columns rows]
+  (with-out-str
+    ;; turn keywords into strings, otherwise we get colons in our output
+    (csv/write-csv *out* (into [(mapv name columns)] rows))))
+
 (defn- export-to-json [columns rows]
   (for [row rows]
     (zipmap columns row)))

test/metabase/api/dataset_test.clj

 (ns metabase.api.dataset-test
   "Unit tests for /api/dataset endpoints."
-  (:require [expectations :refer :all]
+  (:require [cheshire.generate :as generate]
+            [dk.ative.docjure.spreadsheet :as spreadsheet]
+            [expectations :refer :all]
             [medley.core :as m]
             [metabase.api.dataset :refer [default-query-constraints]]
             [metabase.models.query-execution :refer [QueryExecution]]
@@ -128,3 +130,26 @@
                                                                         :native   {:query "foobar"}})]
     [(check-error-message (format-response result))
      (check-error-message (format-response (most-recent-query-execution)))]))
+
+
+;;; Make sure that we're piggybacking off of the JSON encoding logic when encoding strange values in XLSX (#5145, #5220, #5459)
+(defrecord ^:private SampleNastyClass [^String v])
+
+(generate/add-encoder
+ SampleNastyClass
+ (fn [obj, ^com.fasterxml.jackson.core.JsonGenerator json-generator]
+   (.writeString json-generator (:v obj))))
+
+(defrecord ^:private AnotherNastyClass [^String v])
+
+(expect
+  [{"Values" "values"}
+   {"Values" "Hello XLSX World!"}   ; should use the JSON encoding implementation for object
+   {"Values" "{:v \"No Encoder\"}"} ; fall back to the implementation of `str` for an object if no JSON encoder exists rather than barfing
+   {"Values" "ABC"}]
+  (->> (spreadsheet/create-workbook "Results" [["values"]
+                                               [(SampleNastyClass. "Hello XLSX World!")]
+                                               [(AnotherNastyClass. "No Encoder")]
+                                               ["ABC"]])
+       (spreadsheet/select-sheet "Results")
+       (spreadsheet/select-columns {:A "Values"})))