SaveChanges 失败后的 EF Core 修复问题

Question

I have this piece of code (in Asp.net core), I try to add a list of objects to DB:

try
   {
      await _context.AddRangeAsync(mhUserAtts);
      await _context.SaveChangesAsync();
   }
catch()
   {

   }

When some objects conflict with DB, how can I remove them from the list? And then return to save the rest to DB.

Answer 1

In addition to suggested answer in comment, If you want the single query to be executed for entry, you can filter already existing records and attempt to add those which are new as following.

try
   {
      var userAttsInDb =  await _context.UserAtt.Where(u => mhUserAtts.Any(x => x.Id == 
         u.Id)).Select(u => u.Id).ToArrayAsync();
      var mhUserAttsToAdd= mhUserAtts.Where(u => !userAttsInDb.Contains(u.Id));

      await _context.AddRangeAsync(mhUserAttsToAdd);
      await _context.SaveChangesAsync();
   }
catch(){ }

Note: you may need to handle async await properly.

Answer 2

Use transactions (if you db supports it)

public async Task MyDataProcessingAsync(CancellationToken token) {
        using var context = new DbContext();
        using var transaction = await context.Database.BeginTransactionAsync(token);
        try {
            // adding, removing, updating...
            await context.SaveChangesAsync(token);
            await transaction.CommitAsync(token);
        }
        catch {
            // undo all changes
            await transaction.RollbackAsync();
            throw;
        }
    }