发表新帖
发表新帖

How to implement Select For Update in EF Core

前端 未结
关注
2 1057
鱼传尺愫
鱼传尺愫 2021-01-13 03:03

As far as I\'ve understood it, there is no option in EF (and EF Core) to explicitly lock resources which I\'m querying, but I\'ll need this functionality quite often and don

2条回答
  • 佛祖请我去吃肉
    佛祖请我去吃肉 (楼主)
    2021-01-13 03:51

    This work's for me using SQLServer (no tested async methods):

    First, create a DbCommandInterceptor (I called HintInterceptor.cs)

    using System;
using System.Data.Common;
using System.Data.Entity.Infrastructure.Interception;
using System.Text.RegularExpressions;

public class HintInterceptor : DbCommandInterceptor
{
    private static readonly Regex _tableAliasRegex = new Regex(@"(?FROM +(\[.*\]\.)?(\[.*\]) AS (\[.*\])(?! WITH \(*HINT*\)))", RegexOptions.Multiline | RegexOptions.IgnoreCase | RegexOptions.Compiled);

    [ThreadStatic]
    public static string HintValue;

    private static string Replace(string input)
    {
        if (!String.IsNullOrWhiteSpace(HintValue))
        {
            if (!_tableAliasRegex.IsMatch(input))
            {
                throw new InvalidProgramException("Não foi possível identificar uma tabela para ser marcada para atualização(forupdate)!", new Exception(input));
            }
            input = _tableAliasRegex.Replace(input, "${tableAlias} WITH (*HINT*)");
            input = input.Replace("*HINT*", HintValue);
        }
        HintValue = String.Empty;
        return input;
    }

    public override void ScalarExecuting(DbCommand command, DbCommandInterceptionContext interceptionContext)
    {
        command.CommandText = Replace(command.CommandText);
    }

    public override void ReaderExecuting(DbCommand command, DbCommandInterceptionContext interceptionContext)
    {
        command.CommandText = Replace(command.CommandText);
    }
}



    So into Web.config register the your interceptor class
    


    


  

 
  



    


    Now I create a static class called HintExtension
    


    public static class HintExtension
{
    public static IQueryable WithHint(this IQueryable set, string hint) where T : class
    {
        HintInterceptor.HintValue = hint;
        return set;
    }
    public static IQueryable ForUpdate(this IQueryable set) where T : class
    {
        return set.WithHint("UPDLOCK");
    }
}

    


    That's All, I can use inside a database transaction like:
    


    using(var trans = context.Database.BeginTransaction())
{
        var query = context.mydbset.Where(a => a.name == "asd").ForUpdate();
        // not locked yet
        var mylist = query.ToList();
        // now are locked for update
        // update the props, call saveChanges() and finally call commit ( or rollback)
        trans.Commit();
        // now are unlocked
}

    


    Sorry for my English, I hope my example will help.
    
    
    
             
    
                                                        
    
            
            
    
              
                
                0
              
                   
                
               讨论(0)
              
                                                  
              
              
    
                          
             
       
          
              
    
                                       
    

    

                
    
                         
          
                              			
        
        
        
    
          
    
            
            
    
              
              
    
            
    


                                 
              
    
            
    
                          
    

        
         
    
                
                
    
                  
                
    
                
    
                   看不清?
                
    
              
    
                                  
    
                    
   
                 
             
              
    提交回复
    
            
    
          
    
        
    
      
       
      
    
    
    
          
 
     
 
    
        
    热议问题