发表新帖
发表新帖

Change table name at runtime

后端 未结
关注
7 1896
陌清茗
陌清茗 2020-12-17 03:22

Lets suppose that I have a db table with name Employee and a respective EF 6.0 db-first model.

Getting all rows of table Employee is done through q

7条回答
  • 甜味超标
    甜味超标 (楼主)
    2020-12-17 04:04

    I know it's been been a while since the original post, but I'll add my answer to help someone else. I had generic SQL queue tables with different table names. I.e. the schema is exactly the same for both tables. I created a framework so that you can dynamically poll the table of your choice by providing the name and that's why I needed to update the table name at run-time. Basically, you can create an interceptor to intercept the raw SQL queries from entity framework and update the table name from there.

    public class MyInterceptor : IDbCommandInterceptor
{
    private const string TableReplaceString = "[TheTableNameToReplace]";

    private void ReplaceTableName(DbCommand command, IEnumerable contexts)
    {
        var myContext = contexts?.FirstOrDefault(x => x is MyContext) as MyContext;
        if (myContext != null && command != null && command.CommandText.Contains(TableReplaceString))
        {
            command.CommandText = command.CommandText.Replace(TableReplaceString, $"[{myContext.NewTableName}]");
        }
    }

    public void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext interceptionContext)
    {
        ReplaceTableName(command, interceptionContext.DbContexts);
    }

    public void NonQueryExecuted(DbCommand command, DbCommandInterceptionContext interceptionContext)
    {
        ReplaceTableName(command, interceptionContext.DbContexts);
    }

    public void ReaderExecuting(DbCommand command, DbCommandInterceptionContext interceptionContext)
    {
        ReplaceTableName(command, interceptionContext.DbContexts);
    }

    public void ReaderExecuted(DbCommand command, DbCommandInterceptionContext interceptionContext)
    {
        ReplaceTableName(command, interceptionContext.DbContexts);
    }

    public void ScalarExecuting(DbCommand command, DbCommandInterceptionContext interceptionContext)
    {
        ReplaceTableName(command, interceptionContext.DbContexts);
    }

    public void ScalarExecuted(DbCommand command, DbCommandInterceptionContext interceptionContext)
    {
        ReplaceTableName(command, interceptionContext.DbContexts);
    }
}



    Of course, you have to get the new table name from somewhere.  Either from the constructor or from a stored field in your custom DBContext which you can grab from interceptionContext.DbContexts.
    


    Then you just have to register the interceptor for your context.
    


    public class MyContext : DBContext
{
    public readonly string NewTableName;

    public MyContext(string connectionString, string newTableName)
        : base(connectionString)
    {
        NewTableName = newTableName;
        // Set interceptor
        DbInterception.Add(new MyInterceptor());
    }
}

    


    UPDATE:
I found that if you add the interceptor in the constructor above will cause memory leaks.  DotMemory doesn't tell you about this.  Make sure you add the interceptor in a static constructor instead.
    


    public class MyContext : DBContext
{
    public readonly string NewTableName;

    static MyContext()
    {
        // Set interceptor only in static constructor
        DbInterception.Add(new MyInterceptor());
    }

    public MyContext(string connectionString, string newTableName)
        : base(connectionString)
    {
        NewTableName = newTableName;
    }
}

    
    
    
             
    
                                                        
    
            
            
    
              
                
                0
              
                   
                
               讨论(0)
              
                                                  
              
              
    
                          
             
       
          
              
    
                                       
    

    

                
    
                         
          
                              			
        
        
        
    
          
    
            
            
    
              
              
    
            
    


                                 
              
    
            
    
                          
    

        
         
    
                
                
    
                  
                
    
                
    
                   看不清?
                
    
              
    
                                  
    
                    
   
                 
             
              
    提交回复
    
            
    
          
    
        
    
      
       
      
    
    
    
          
 
     
 
    
        
    热议问题