Optimal way to add / update EF entities if added items may or may not already exist

I need some guidance on adding / updating SQL records using EF. Lets say I am writing an application that stores info about files on a hard disk, into an EF4 database. When you press a button, it will scan all the files in a specified path (maybe the whole drive), and store information in the database like the file size, change date etc. Sometimes the file will already be recorded from a previous run, so its properties should be updated; sometimes a batch of files will be detected for the first time and will need to be added.

I am using EF4, and I am seeking the most efficient way of adding new file information and updating existing records. As I understand it, when I press the search button and files are detected, I will have to check for the presence of a file entity, retrieve its ID field, and use that to add or update related information; but if it does not exist already, I will need to create a tree that represents it and its related objects (eg. its folder path), and add that. I will also have to handle the merging of the folder path object as well.

It occurs to me that if there are many millions of files, as there might be on a server, loading the whole database into the context is not ideal or practical. So for every file, I might conceivably have to make a round trip to the database on disk to detect if the entry exists already, re开发者_JS百科trieve its ID if it exists, then another trip to update. Is there a more efficient way I can insert/update multiple file object trees in one trip to the DB? If there was an Entity context method like 'Insert If It Doesnt Exist And Update If It Does' for example, then I could wrap up multiple in a transaction?

I imagine this would be a fairly common requirement, how is it best done in EF? Any thoughts would be appreciated.(oh my DB is SQLITE if that makes a difference)

You can check if the record already exists in the DB. If not, create and add the record. You can then set the fields of the record which will be common to insert and update like the sample code below.

           var strategy_property_in_db = _dbContext.ParameterValues().Where(r => r.Name == strategy_property.Name).FirstOrDefault();
            if (strategy_property_in_db == null)
            {
                strategy_property_in_db = new ParameterValue() { Name = strategy_property.Name };
                _dbContext.AddObject("ParameterValues", strategy_property_in_db);
            }
            strategy_property_in_db.Value = strategy_property.Value;