暂时添加了 邮箱不可重复申请帐号

后续改成 邮箱可以申请多个账号， 用邮箱登陆时选择帐号登陆
修改了 MessageSystem 结构

MessageSystem/message_base/db_base.h

@@ -0,0 +1,32 @@
+//
+// Created by dongl on 23-5-29.
+//
+
+#ifndef IM2_DB_BASE_H
+#define IM2_DB_BASE_H
+
+#include <mongocxx/pool.hpp>
+#include <mongocxx/stdx.hpp>
+#include <bsoncxx/stdx/optional.hpp>
+#include <mongocxx/client.hpp>
+
+using bsoncxx::builder::basic::kvp;
+using bsoncxx::builder::basic::make_array;
+using bsoncxx::builder::basic::make_document;
+
+class db_base {
+public:
+    db_base();
+    mongocxx::pool::entry acquire();
+    bsoncxx::stdx::optional<mongocxx::pool::entry> try_acquire();
+
+public:
+    // 命中 库 表
+    mongocxx::collection hit_db_coll(const std::string& db_name, const std::string& coll);
+
+private:
+    mongocxx::pool* pool = nullptr;
+};
+
+
+#endif //IM2_DB_BASE_H