diff --git a/design.txt b/design.txt
index c15866a..94d18eb 100644
--- a/design.txt
+++ b/design.txt
@@ -155,7 +155,7 @@
 		当新的类型名称发生冲突
 		
 		副作用:
-		改变图书种类会引起所有与原种类相关图书的信息变更
+		改变图书种类会引起所有与原种类相关图书的信息变更(未实现)
 	
 	http://booksys.com/api/v1/removebooktype POST
 		POST:
@@ -164,7 +164,7 @@
 		错误:
 		当任一图书定义使用此定义时将不能删除图书种类
 		
-	http://booksys.com/api/v1/register POST
+	http://booksys.com/api/v1/join POST
 		POST:
 		account
 		pass
diff --git a/join.cpp b/join.cpp
new file mode 100644
index 0000000..983698b
--- /dev/null
+++ b/join.cpp
@@ -0,0 +1,122 @@
+#include "Session.h"
+#include "Util.h"
+#include "json.hpp"
+#include "jsonfail.h"
+using namespace std;
+using json=nlohmann::json;
+
+#define postval(NAME) string NAME=req.post[#NAME]
+
+int main()
+{
+    Request req;
+    Session se(req);
+    Response res;
+    json j;
+
+    auto jsonfail=[&](int errcode,const string& detail="")
+    {
+        j["success"]=0;
+        j["errcode"]=errcode;
+        j["errmsg"]=string(GetErrMsg(errcode))+" : "+detail;
+    };
+
+    do
+    {
+        if(!se.isReady())
+        {
+            jsonfail(err_session);
+            break;
+        }
+        if(!se.getUser().empty())
+        {
+            /// Logged in. Redirect user to dashboard.
+            j["success"]=2;
+            j["next_url"]="/booksys/dashboard.html";
+            break;
+        }
+
+        if(req.requestMethod!="POST")
+        {
+            jsonfail(err_method_not_supported);
+            break;
+        }
+
+        if(req.post["account"].empty() ||
+           req.post["pass"].empty() ||
+           req.post["nickname"].empty())
+        {
+            jsonfail(err_missing_parameter);
+            break;
+        }
+
+        postval(account);
+        postval(pass);
+        postval(nickname);
+
+        /// Connect DB
+        DBInfo db;
+        MySQLConn conn;
+        if(db.readConfig()<0)
+        {
+            jsonfail(err_config);
+            break;
+        }
+
+        if(db.connectProxy(conn)<0)
+        {
+            jsonfail(err_connect);
+            break;
+        }
+
+        /// Check username conflict
+        int count_val;
+        if(conn.exec(make_str("select count(username) from bs_user where username='",
+                              account,
+                              "'"),
+                     [&](MySQLResult& res)
+                     {
+                         res.stepRow([&](char** val,unsigned long* len)
+                                     {
+                                         count_val=ParseInt(val[0]);
+                                     });
+                     })<0)
+        {
+            jsonfail(err_sql);
+            break;
+        }
+
+        if(count_val!=0)
+        {
+            jsonfail(err_data,"username conflict");
+            break;
+        }
+
+        /// Do insert
+        if(conn.exec(make_str("insert into bs_user values ('",
+                              account,
+                              "','",
+                              pass,
+                              "','",
+                              nickname,
+                              "',3,2"),nullptr)<0)
+        {
+            jsonfail(err_sql);
+            break;
+        }
+
+        if(conn.getAffectedRows()!=1)
+        {
+            jsonfail(err_sql_logic,"Affected rows not equals 1");
+            break;
+        }
+
+        /// Redirect user to enable page.
+        j["success"]=1;
+        j["next_url"]="/booksys/enable.html";
+    }while(0);
+
+    res.content.append(j.dump());
+    res.show();
+    return 0;
+}
diff --git a/jsonfail.cpp b/jsonfail.cpp
index 4e604a4..9604ef6 100644
--- a/jsonfail.cpp
+++ b/jsonfail.cpp
@@ -22,6 +22,8 @@ const char* GetErrMsg(int errcode)
         return "Permission denied";
     case err_data:
         return "Data Error";
+    case err_session:
+        return "Session Error";
     default:
         return "General error";
     }
diff --git a/jsonfail.h b/jsonfail.h
index 9b21119..f2205e7 100644
--- a/jsonfail.h
+++ b/jsonfail.h
@@ -9,5 +9,6 @@
 #define err_sql_logic 7
 #define err_permission_denied 8
 #define err_data 9
+#define err_session 10
 
 const char* GetErrMsg(int errcode);
diff --git a/register.cpp b/register.cpp
deleted file mode 100644
index e69de29..0000000