AddOnce Seed extension for EF 6 using LinqKit

EFExtensions.cs

public static class Extensions
{
    public static void AddOnce<TEntity>(
        this IDbSet<TEntity> set,
        Expression<Func<TEntity, object>> identifierExpression,
        params TEntity[] entities) where TEntity : class
    {
        if (set == null) throw new ArgumentNullException("set");
        if (identifierExpression == null) throw new ArgumentNullException("identifierExpression");
        if (entities == null) throw new ArgumentNullException("entities");

        var query = set.AsExpandable();
        var getIdentifier = identifierExpression.Compile();

        foreach (var entity in entities)
        {
            var entityIdentifier = getIdentifier(entity);
            if (!query
                .Any(i => identifierExpression.Invoke(i) == entityIdentifier))
            {
                set.Add(entity);
            }
        }
    }
}