kvstore: simplified stmt exec iterator (#467)

eth/db/kvstore_sqlite3.nim

@@ -211,6 +211,48 @@ proc exec*[Params, Res](s: SqliteStmt[Params, Res],
     discard sqlite3_reset(s) # same return information as step
     discard sqlite3_clear_bindings(s) # no errors possible
 
+iterator exec*[Params, Res](s: SqliteStmt[Params, Res],
+                            params: Params, item: var Res): KvResult[void] =
+  let s = RawStmtPtr s
+
+  # we use a mutable `res` variable here to avoid the code bloat that multiple
+  # `yield` statements cause when inlining the loop body
+  var res = KvResult[void].ok()
+  when params is tuple:
+    var i = 1
+    for param in fields(params):
+      if (let v = bindParam(s, i, param); v != SQLITE_OK):
+        res = KvResult[void].err($sqlite3_errstr(v))
+        break
+
+      inc i
+  else:
+    if (let v = bindParam(s, 1, params); v != SQLITE_OK):
+      res = KvResult[void].err($sqlite3_errstr(v))
+
+  defer:
+    # release implicit transaction
+    discard sqlite3_reset(s) # same return information as step
+    discard sqlite3_clear_bindings(s) # no errors possible
+
+  while res.isOk():
+    let v = sqlite3_step(s)
+    case v
+    of SQLITE_ROW:
+      item = readResult(s, Res)
+      yield KvResult[void].ok()
+    of SQLITE_DONE:
+      break
+    else:
+      res = KvResult[void].err($sqlite3_errstr(v))
+
+  if not res.isOk():
+    yield res
+
+iterator exec*[Res](s: SqliteStmt[NoParams, Res], item: var Res): KvResult[void] =
+  for r in exec(s, (), item):
+    yield r
+
 template exec*(s: SqliteStmt[NoParams, void]): KvResult[void] =
   exec(s, ())
 

tests/db/test_kvstore_sqlite3.nim

@@ -225,3 +225,11 @@ procSuite "SqStoreRef":
       check:
         selectRes.isOk and selectRes.get == true
         abc == val
+
+      var found = false
+      var row: selectStmt.Result
+      for rowRes in selectStmt.exec(row):
+        rowRes.expect("working db")
+        check abc == row
+        found = true
+      check found