How would you write an Upsert for LINQ to SQL?

Question

So I\'d like to write a generic Upsert function for LINQ to SQL and I\'m having some trouble conceptualizing how to do it. I\'d like it to work something like this:

Answer 1

Short Answer:

Grab this: EntityExtensionMethods.cs

Explanation

To do UPSERT in LINQ-to-SQL without querying the records first, you can do the following. It will still hit the db once to check if record exists but will not pull the record:

var blob = new Blob { Id = "some id", Value = "some value" }; // Id is primary key (PK)

if (dbContext.Blobs.Contains(blob)) // if blob exists by PK then update
{
    // This will update all columns that are not set in 'original' object. For
    // this to work, Blob has to have UpdateCheck=Never for all properties except
    // for primary keys. This will update the record without querying it first.
    dbContext.Blobs.Attach(blob, original: new Blob { Id = blob.Id });
}
else // insert
{
    dbContext.Blobs.InsertOnSubmit(blob);
}
dbContext.Blobs.SubmitChanges();

Extension Method

I came up with the following extension method for it.

public static class EntityExtensionMethods
{
    public static void InsertOrUpdateOnSubmit(this Table table, TEntity entity, TEntity original = null)
        where TEntity : class, new()
    {
        if (table.Contains(entity)) // if entity exists by PK then update
        {
            if (original == null)
            {
                // Create original object with only primary keys set
                original = new TEntity();
                var entityType = typeof(TEntity);
                var dataMembers = table.Context.Mapping.GetMetaType(entityType).DataMembers;
                foreach (var member in dataMembers.Where(m => m.IsPrimaryKey))
                {
                    var propValue = entityType.GetProperty(member.Name).GetValue(entity, null);
                    entityType.InvokeMember(member.Name, BindingFlags.SetProperty, Type.DefaultBinder,
                        original, new[] {propValue});
                }
            }

            // This will update all columns that are not set in 'original' object. For
            // this to work, entity has to have UpdateCheck=Never for all properties except
            // for primary keys. This will update the record without querying it first.
            table.Attach(entity, original);
        }
        else // insert
        {
            table.InsertOnSubmit(entity);
        }
    }
}

Use it like below:

var blob = new Blob { Id = "some id", Value = "some value" }; // Id is primary key (PK)
dbContext.Blobs.InsertOrUpdateOnSubmit(blob);
dbContext.Blobs.SubmitChanges();

I added above extension method with more stuff to this gist: EntityExtensionMethods.cs