public static async Task InsertUpdateOrDeleteGraphAsync(BloggingContext context, Blog blog)
{
var existingBlog = await context.Blogs
.Include(b => b.Posts)
.FirstOrDefaultAsync(b => b.BlogId == blog.BlogId);
if (existingBlog == null)
{
context.Add(blog);
}
else
{
context.Entry(existingBlog).CurrentValues.SetValues(blog);
foreach (var post in blog.Posts)
{
var existingPost = existingBlog.Posts
.AsQueryable()
.FirstOrDefaultAsync(p => p.PostId == post.PostId);
if (existingPost == null)
{
existingBlog.Posts.Add(post);
}
else
{
context.Entry(existingPost).CurrentValues.SetValues(post);
}
}
foreach (var post in existingBlog.Posts)
{
if (!blog.Posts.Any(p => p.PostId == post.PostId))
{
context.Remove(post);
}
}
}
await context.SaveChangesAsync();
}
private static async Task IsItNewAsync()
{
Console.WriteLine();
Console.WriteLine("Show entity-specific check for key set:");
await using (var context = new BloggingContext())
{
var blog = new Blog {
Url = "http://sample.com"
};
// Key is not set for a new entity
Console.WriteLine($" Blog entity is {(IsItNew(blog) ? "new" : "existing")}.");
context.Add(blog);
await context.SaveChangesAsync();
// Key is now set
Console.WriteLine($" Blog entity is {(IsItNew(blog) ? "new" : "existing")}.");
}
Console.WriteLine();
Console.WriteLine("Show general IsKeySet:");
await using (var context = new BloggingContext())
{
var blog = new Blog {
Url = "http://sample.com"
};
// Key is not set for a new entity
Console.WriteLine($" Blog entity is {(IsItNew(context, (object)blog) ? "new" : "existing")}.");
context.Add(blog);
await context.SaveChangesAsync();
// Key is now set
Console.WriteLine($" Blog entity is {(IsItNew(context, (object)blog) ? "new" : "existing")}.");
}
Console.WriteLine();
Console.WriteLine("Show key set on Add:");
await using (var context = new BloggingContext())
{
var blog = new Blog {
Url = "http://sample.com"
};
// Key is not set for a new entity
Console.WriteLine($" Blog entity is {(IsItNew(context, (object)blog) ? "new" : "existing")}.");
context.Add(blog);
// Key is set as soon as Add assigns a key, even if it is temporary
Console.WriteLine($" Blog entity is {(IsItNew(context, (object)blog) ? "new" : "existing")}.");
}
Console.WriteLine();
Console.WriteLine("Show using query to check for new entity:");
await using (var context = new BloggingContext())
{
var blog = new Blog {
Url = "http://sample.com"
};
Console.WriteLine($" Blog entity is {(IsItNewAsync(context, blog) ? "new" : "existing")}.");
context.Add(blog);
await context.SaveChangesAsync();
Console.WriteLine($" Blog entity is {(IsItNewAsync(context, blog) ? "new" : "existing")}.");
}
}