How to discard changes to context in EF Core

问题

I have a huge list of "flattened" objects in json format, and a somewhat complicated relational DB schema (with about 20 tables corresponding to a flattened object). I'm trying to automate the insertions of those flattened objects in my new relational database:

foreach (var flattenedObject in flattenedObjects)
{
    _repository.Insert(flattenedObject).Wait();
    //some time logging, etc
}

The Insert() method callsAddRangeAsync() and AddAsync() for a number of related objects in different tables.

Since the flattened objects are legacy, I'd say about 0.001% of them are malformed and will violate DB constraints - for example trying to insert a duplicate composite primary key in one of the tables.

I expect these rare errors, thus my idea is - wrap the whole Insert() operation in a transaction - if any piece of the operation is invalid, just don't insert anything and log the error, so I can modify the flattened object manually before trying again. Thus my code looks somewhat similar to this:

public async Task Insert(FlattenedObject fo)
{
    using (var transaction = _context.Database.BeginTransaction())
    {
        try
        {
            //magical code that calls AddAsync for multiple tables
        }
        catch (Exception ex)
        {
            transaction.Rollback()
            //logging
        }
    }
}

However, if an error occurs somewhere in my try block (I try to insert an object that violates a composite primary key) my whole context object becomes corrupt.

The object that caused the exception still remains in my DbContext and any following call to AddAsync() in a different transaction triggers a new exception.

I tried recreating my DbContext and repo for every new object in the foreach loop above - but even then if I query:

_context.ChangeTracker.Entries().Where(e => e.State != EntityState.Unchanged);

I see my old object is still in the new instance of dbContext.

Is there any (elegant) way to tell my context to reset all pending changes - so that I can put it in the catch block whenever an error occurs? I want everything that happens within my failed transaction to stay there and not leak.

回答1:

The code below worked for me. However, if someone posts a cleaner solution (I still expect there to be something out of the box with EF) I will accept it.

private void ResetContextState() => _context.ChangeTracker.Entries()
    .Where(e => e.Entity != null).ToList()
    .ForEach(e => e.State = EntityState.Detached);

来源：https://stackoverflow.com/questions/42885020/how-to-discard-changes-to-context-in-ef-core