public static void UpdatePostsFromJsonWithIdentityResolution(string json)
{
using var context = new BlogsContext();
var posts = JsonConvert.DeserializeObject <List <Post> >(json);
foreach (var post in posts)
{
context.ChangeTracker.TrackGraph(
post, node =>
{
var keyValue = node.Entry.Property("Id").CurrentValue;
var entityType = node.Entry.Metadata;
var existingEntity = node.Entry.Context.ChangeTracker.Entries()
.FirstOrDefault(
e => Equals(e.Metadata, entityType) &&
Equals(e.Property("Id").CurrentValue, keyValue));
if (existingEntity == null)
{
Console.WriteLine($"Tracking {entityType.DisplayName()} entity with key value {keyValue}");
node.Entry.State = EntityState.Modified;
}
else
{
Console.WriteLine($"Discarding duplicate {entityType.DisplayName()} entity with key value {keyValue}");
}
});
}
context.SaveChanges();
}
public static void UpdateBlogsFromJson(string json)
{
using var context = new BlogsContext();
var blogs = JsonConvert.DeserializeObject <List <Blog> >(json);
foreach (var blog in blogs)
{
context.Update(blog);
}
context.SaveChanges();
}
public static void UpdatePostsFromJson(string json)
{
using var context = new BlogsContext();
var posts = JsonConvert.DeserializeObject <List <Post> >(json);
foreach (var post in posts)
{
context.Update(post);
}
context.SaveChanges();
}
public static void PopulateDatabase()
{
using var context = new BlogsContext(quiet: true);
context.AddRange(
new Blog
{
Name = ".NET Blog",
Summary = "Posts about .NET",
Posts =
{
new Post
{
Title = "Announcing the Release of EF Core 5.0",
Content = "Announcing the release of EF Core 5.0, a full featured cross-platform..."
},
new Post
{
Title = "Announcing F# 5",
Content = "F# 5 is the latest version of F#, the functional programming language..."
},
},
},
new Blog
{
Name = "Visual Studio Blog",
Summary = "Posts about Visual Studio",
Posts =
{
new Post
{
Title = "Disassembly improvements for optimized managed debugging",
Content =
"If you are focused on squeezing out the last bits of performance for your .NET service or..."
},
new Post
{
Title = "Database Profiling with Visual Studio",
Content = "Examine when database queries were executed and measure how long the take using..."
},
}
});
context.SaveChanges();
}
public static void UpdatePostsFromJsonBad(string json)
{
using var context = new BlogsContext();
var posts = JsonConvert.DeserializeObject <List <Post> >(json);
try
{
foreach (var post in posts)
{
context.Update(post); // Will throw
}
context.SaveChanges();
}
catch (Exception e)
{
Console.WriteLine($"{e.GetType().FullName}: {e.Message}");
}
}
