基于 EntityFramework 的数据库主从读写分离架构（2）- 改进配置和添加事务支持

 1  public class DbMasterSlaveCommandInterceptor : DbCommandInterceptor
 2     {
 3         private Lazy<string> masterConnectionString = new Lazy<string>(() => ConfigurationManager.AppSettings["masterConnectionString"]);
 4         private Lazy<string> slaveConnectionString = new Lazy<string>(() => ConfigurationManager.AppSettings["slaveConnectionString"]);
 5  
 6         public string MasterConnectionString
 7         {
 8             get { return this.masterConnectionString.Value; }
 9         }
10  
11         public string SlaveConnectionString
12         {
13             get { return this.slaveConnectionString.Value; }
14         }
15  
16  
17         public override void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
18         {
19             this.UpdateConnectionStringIfNeed(interceptionContext, this.SlaveConnectionString);
20         }
21  
22         public override void ScalarExecuting(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
23         {
24             this.UpdateConnectionStringIfNeed(interceptionContext, this.SlaveConnectionString);
25         }
26  
27         public override void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
28         {
29             this.UpdateConnectionStringIfNeed(interceptionContext, this.MasterConnectionString);
30         }
31  
32  
33         private void UpdateConnectionStringIfNeed(DbInterceptionContext interceptionContext, string connectionString)
34         {
35             foreach (var context in interceptionContext.DbContexts)
36             {
37                 this.UpdateConnectionStringIfNeed(context.Database.Connection, connectionString);
38             }
39         }
40  
41         /// <summary>
42         /// 此处改进了对连接字符串的修改判断机制，确认只在 <paramref name="conn"/> 所使用的连接字符串不等效于 <paramref name="connectionString"/> 的情况下才需要修改。
43         /// </summary>
44         /// <param name="conn"></param>
45         /// <param name="connectionString"></param>
46         private void UpdateConnectionStringIfNeed(DbConnection conn, string connectionString)
47         {
48             if (this.ConnectionStringCompare(conn, connectionString))
49             {
50                 ConnectionState state = conn.State;
51                 if (state == ConnectionState.Open)
52                     conn.Close();
53  
54                 conn.ConnectionString = connectionString;
55  
56                 if (state == ConnectionState.Open)
57                     conn.Open();
58             }
59         }
60  
61         private bool ConnectionStringCompare(DbConnection conn, string connectionString)
62         {
63             DbProviderFactory factory = DbProviderFactories.GetFactory(conn);
64  
65             DbConnectionStringBuilder a = factory.CreateConnectionStringBuilder();
66             a.ConnectionString = conn.ConnectionString;
67  
68             DbConnectionStringBuilder b = factory.CreateConnectionStringBuilder();
69             b.ConnectionString = connectionString;
70  
71             return a.EquivalentTo(b);
72         }
73     }

 1 public class DbMasterSlaveCommandInterceptor : DbCommandInterceptor
 2     {
 3         private Lazy<string> masterConnectionString = new Lazy<string>(() => ConfigurationManager.AppSettings["masterConnectionString"]);
 4         private Lazy<string> slaveConnectionString = new Lazy<string>(() => ConfigurationManager.AppSettings["slaveConnectionString"]);
 5  
 6         public string MasterConnectionString
 7         {
 8             get { return this.masterConnectionString.Value; }
 9         }
10  
11         public string SlaveConnectionString
12         {
13             get { return this.slaveConnectionString.Value; }
14         }
15  
16  
17         public override void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
18         {
19             this.UpdateToSlave(interceptionContext);
20         }
21  
22         public override void ScalarExecuting(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
23         {
24             this.UpdateToSlave(interceptionContext);
25         }
26  
27         public override void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
28         {
29             this.UpdateToMaster(interceptionContext);
30         }
31  
32  
33         private void UpdateToMaster(DbInterceptionContext interceptionContext)
34         {
35             foreach (var context in interceptionContext.DbContexts)
36             {
37                 this.UpdateConnectionStringIfNeed(context.Database.Connection, this.MasterConnectionString);
38             }
39         }
40  
41         private void UpdateToSlave(DbInterceptionContext interceptionContext)
42         {
43             // 判断当前会话是否处于分布式事务中
44             bool isDistributedTran = Transaction.Current != null && Transaction.Current.TransactionInformation.Status != TransactionStatus.Committed;
45             foreach (var context in interceptionContext.DbContexts)
46             {
47                 // 判断该 context 是否处于普通数据库事务中
48                 bool isDbTran = context.Database.CurrentTransaction != null;
49  
50                 // 如果处于分布式事务或普通事务中，则“禁用”读写分离，处于事务中的所有读写操作都指向 Master
51                 string connectionString = isDistributedTran || isDbTran ? this.MasterConnectionString : this.SlaveConnectionString;
52  
53                 this.UpdateConnectionStringIfNeed(context.Database.Connection, connectionString);
54             }
55         }
56  
57  
58         /// <summary>
59         /// 此处改进了对连接字符串的修改判断机制，确认只在 <paramref name="conn"/> 所使用的连接字符串不等效于 <paramref name="connectionString"/> 的情况下才需要修改。
60         /// <para>同时，在必要的情况下才会连接进行 Open 和 Close 操作以及修改 ConnectionString 处理，减少了性能的消耗。</para>
61         /// </summary>
62         /// <param name="conn"></param>
63         /// <param name="connectionString"></param>
64         private void UpdateConnectionStringIfNeed(DbConnection conn, string connectionString)
65         {
66             if (this.ConnectionStringCompare(conn, connectionString))
67             {
68                 this.UpdateConnectionString(conn, connectionString);
69             }
70         }
71  
72         private void UpdateConnectionString(DbConnection conn, string connectionString)
73         {
74             ConnectionState state = conn.State;
75             if (state == ConnectionState.Open)
76                 conn.Close();
77  
78             conn.ConnectionString = connectionString;
79  
80             if (state == ConnectionState.Open)
81                 conn.Open();
82         }
83  
84         private bool ConnectionStringCompare(DbConnection conn, string connectionString)
85         {
86             DbProviderFactory factory = DbProviderFactories.GetFactory(conn);
87  
88             DbConnectionStringBuilder a = factory.CreateConnectionStringBuilder();
89             a.ConnectionString = conn.ConnectionString;
90  
91             DbConnectionStringBuilder b = factory.CreateConnectionStringBuilder();
92             b.ConnectionString = connectionString;
93  
94             return a.EquivalentTo(b);
95         }
96     }