diff --git a/packages/bookshop/srv/utils.js b/packages/bookshop/srv/utils.js
new file mode 100644
index 00000000..b05b932d
--- /dev/null
+++ b/packages/bookshop/srv/utils.js
@@ -0,0 +1,33 @@
+const diff = (obj1, obj2) =>
+  Object.keys(obj1).reduce(
+    (res, curr) =>
+      obj1[curr] === obj2[curr] ? res : (res[curr] = obj2[curr]) && res,
+    {}
+  )
+
+const queriesToUpdateDifferences = (entity, ownEntries, otherEntries) =>
+  ownEntries
+    .map(ownEntry => {
+      const remoteAddress = otherEntries.find(otherEntry =>
+        Object.keys(entity.keys).reduce(
+          (res, curr) => res && otherEntry[curr] === ownEntry[curr],
+          true
+        )
+      )
+      if (remoteAddress) {
+        const differences = diff(ownEntry, remoteAddress)
+        if (Object.keys(differences).length) {
+          return UPDATE(entity)
+            .set(differences)
+            .where(
+              Object.keys(entity.keys).reduce(
+                (res, curr) => (res[curr] = ownEntry[curr]) && res,
+                {}
+              )
+            )
+        }
+      }
+    })
+    .filter(el => el)
+
+module.exports = { diff, queriesToUpdateDifferences }