Memoize field-can-be-null?

guix-data-service/model/utils.scm

@@ -145,6 +145,34 @@ WHERE table_name = $1"
                   (string=? is_nullable "YES"))))
          results))))
 
+(define %field-can-be-null-cache
+  (make-hash-table))
+
+(define (field-can-be-null? conn table-name field)
+  (let ((cache-key (cons table-name field)))
+    (match (hash-get-handle %field-can-be-null-cache
+                            cache-key)
+      ((_ . res) res)
+      (#f
+       (let ((schema-details
+              (table-schema conn table-name)))
+         (match (find (lambda (column-data)
+                        (string=? field
+                                  (car column-data)))
+                      schema-details)
+           ((column-name data-type is-nullable?)
+            (hash-set! %field-can-be-null-cache
+                       cache-key
+                       is-nullable?)
+            is-nullable?)
+           (#f
+            (simple-format
+             (current-error-port)
+             "error: couldn't find data for ~A in ~A\n"
+             field
+             schema-details)
+            (error "error: field-can-be-null?"))))))))
+
 (define* (insert-missing-data-and-return-all-ids
           conn
           table-name
@@ -216,23 +244,6 @@ WHERE table_name = $1"
                         (loop (cdr a) (cdr b))
                         a-val)))))))))))
 
-  (define schema-details
-    (table-schema conn table-name))
-
-  (define (field-can-be-null? field)
-    (match (find (lambda (column-data)
-                   (string=? field
-                             (car column-data)))
-                 schema-details)
-      ((column-name data-type is-nullable?) is-nullable?)
-      (#f
-       (simple-format
-        (current-error-port)
-        "error: couldn't find data for ~A in ~A\n"
-        field
-        schema-details)
-       (error "error: field-can-be-null?"))))
-
   (define (select-query data)
     (string-append
      "SELECT id,\n"
@@ -258,7 +269,7 @@ WHERE table_name = $1"
              (string-concatenate
               `("("
                 ,table-name "." ,field " = vals." ,field
-                ,@(if (field-can-be-null? field)
+                ,@(if (field-can-be-null? conn table-name field)
                       `(" OR (" ,table-name "." ,field " IS NULL AND"
                         " vals." ,field " IS NULL"
                         ")")
@@ -282,7 +293,7 @@ WHERE table_name = $1"
              (string-concatenate
               `("("
                 ,table-name "." ,field " = " ,temp-table-name "." ,field
-                ,@(if (field-can-be-null? field)
+                ,@(if (field-can-be-null? conn table-name field)
                       `(" OR ("
                         ,table-name "." ,field " IS NULL"
                         " AND "