Created support muti db (markdown)

support-muti-db.md

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+## appsettings.json
+
+### 1、开启多库操作阀门为true
+
+```
+"MutiDBEnabled": true
+```
+
+### 2、配置多个连接字符串
+
+```
+// 如果要启用那个，就必须开启对应的阀门Enabled为true，
+// 同时必须要配置不同的连接ID —— ConnId
+// 注意♥，多个数据库必须都存在，如果不存在肯定连不上。
+
+  "DBS": [
+    /*
+      MySql = 0,
+      SqlServer = 1,
+      Sqlite = 2,
+      Oracle = 3,
+      PostgreSQL = 4
+    */
+    {
+      "ConnId": "WMBLOG_SQLITE",
+      "DBType": 2,
+      "Enabled": true,
+      "Connection": "WMBlog.db" //只写数据库名就行，我会拼接字符串
+    },
+    {
+      "ConnId": "WMBLOG_MSSQL",
+      "DBType": 1,
+      "Enabled": true,
+      "Connection": "Server=.;Database=WMBlogDB;User ID=sa;Password=123;",
+      "ProviderName": "System.Data.SqlClient"
+    },
+    {
+      "ConnId": "WMBLOG_MYSQL",
+      "DBType": 0,
+      "Enabled": true,
+      "Connection": "Server=localhost; Port=3306;Stmt=; Database=wmblogdb; Uid=root; Pwd=456;"
+    },
+    {
+      "ConnId": "WMBLOG_ORACLE",
+      "DBType": 3,
+      "Enabled": false,
+      "Connection": "Provider=OraOLEDB.Oracle; Data Source=WMBlogDB; User Id=sss; Password=789;",
+      "OracleConnection_other1": "User ID=sss;Password=789;Data Source=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.8.65)(PORT=1521)))(CONNECT_DATA=(SERVICE_NAME = orcl)))"
+    }
+  ],
+
+```
+
+### 3、配置主数据库ID
+
+```
+//在appsettings.json中配置主数据库连接ID
+
+"MainDB": "WMBLOG_SQLITE",//当前项目的主库，连接字符串的Enabled必须为true
+
+```
+
+
+
+### 4、配置实体Model特性，对应的数据库连接Id
+
+// 第一个参数是表名，第二个参数是对应的appsettings.json中的连接id
+// 如果这个特性不写，默认的就是主数据库
+
+```
+    [SugarTable("PasswordLib", "WMBLOG_MSSQL")]
+    public class PasswordLib
+    {
+        [SugarColumn(IsNullable = false, IsPrimaryKey = true, IsIdentity = true)]
+        public int PLID { get; set; }
+        
+        // more...
+
+    }
+```
+