[doc] transactions

docs/_sidebar.md

@@ -30,7 +30,4 @@
     * [Preloading Association](association.md#preloading-association)
     * [Modifying Association](association.md#modifying-association)
 
-* Others
-
-    * Transactions
-    * Logging
+* [Transactions](transactions.md)

docs/index.html

@@ -16,6 +16,7 @@
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       name: 'rel',
+      ga: 'UA-118567391-2',
       repo: 'https://github.com/Fs02/rel',
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       themeColor: '#007d9c',
@@ -33,8 +34,9 @@
       ]
     }
   </script>
-  <script src="//cdn.jsdelivr.net/npm/docsify-tabs@1"></script>
+  <script src="//unpkg.com/docsify/lib/plugins/ga.min.js"></script>
   <script src="//unpkg.com/prismjs/components/prism-go.min.js"></script>
+  <script src="//cdn.jsdelivr.net/npm/docsify-tabs@1"></script>
   <script src="//unpkg.com/prismjs/components/prism-bash.min.js"></script>
 </body>
 </html>

docs/transactions.md

@@ -0,0 +1,31 @@
+# Transactions
+
+To declare a transaction, use `Transaction` method.
+It accepts a function with `rel.Repository` argument and returns an error.
+
+If any error occured within transaction, the transaction will be rolled back, and returns the error.
+If the error is a runtime error or `panic` with string argument, it'll panic after rollback.
+
+<!-- tabs:start -->
+
+### **main.go**
+
+```go
+if err := repo.Transaction(func(repo rel.Repository) error {
+    repo.Update(&books, rel.Dec("stock"))
+    return repo.Update(&transaction, rel.Set("paid", true))
+}); err != nil {
+    // handle error
+}
+```
+
+### **main_test.go**
+
+```go
+repo.ExpectTransaction(func(repo *Repository) {
+    repo.ExpectUpdate(rel.Dec("stock")).ForType("main.Book")
+    repo.ExpectUpdate(rel.Set("paid", true)).ForType("main.Transaction")
+})
+```
+
+<!-- tabs:end -->