Include fields from related tables - ef-core-2.1

Question

I'm using EF with DotNet Core 2.1 in my application. The application deals with data in multiple related and with FK interconnected tables.
I need audit logging data only changes to one table. However, my problem is, the table I need to audit log has quite some FK and for each of these I would like to log the FK itself and a field from the related table.
Let me try illustrate what I'm about - let's suppose this is my model:
public class Blog {
public int Id { get; set; }
public string Name { get; set; }
public string Url { get; set; }
[InverseProperty ("Blog")]
public ICollection<Post> Posts { get; set; }
public Blog() {
Posts = new Collection<Post> ();
}
}
...
[AuditInclude]
public class Post
{
public int Id { get; set; }
public string Title { get; set; }
public string Content { get; set; }
[Required]
public int BlogId { get; set; }
public Blog Blog { get; set; }
}
As said, I'd like audit logging only changes to one entity - let's say it is a Post - here is an audit class:
public class Audit_Post : IAudit {
public int Id { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public int BlogId { get; set; }
public string Blog { get; set; } // <- I need populating this from Blog.Name
[StringLength (64)]
public string AuditUsername { get; set; }
public DateTime AuditDt { get; set; }
public string AuditAction { get; set; }
public Audit_Manufacturer () { }
}
And this is how I set up audit logging in my startup.cs -> ConfigureService():
...
Audit.Core.Configuration.Setup ()
.UseEntityFramework (ef => ef
.AuditTypeExplicitMapper (m => m
.Map<Post, Audit_Post> ((d, al) => {
al.Blog = d.Blog?.Name; // !! This doesn't work
})
.AuditEntityAction<IAudit> ((evt, entry, auditEntity) => {
Object val;
var gotVal = evt.CustomFields.TryGetValue ("AuditUsername", out val);
string username = null;
if (gotVal && val is string)
username = val as string;
else
username = "<anonymous>";
auditEntity.AuditDt = DateTime.UtcNow;
auditEntity.AuditUsername = username;
auditEntity.AuditAction = entry.Action;
})
)
);
question: Is it possible at all to get and audit log data from dependant table (one-to-many) relation?
Beside the mentioned issue, I'm also bumped in an off-topic one, which is - if I forget updating the DB with the migration for initialising the Audit_Posts table and I'm doing operations on Posts table, the data get stored to the later even if audit logs fail to get written (UnitOfWork save exception). Is there a flag to AuditDbContext that would make it run in the same transaction as the original query?

Answer 1

As #thepirat000 pointed out, it is enough to guarantee all related items being present in the DbContext memory. This means:
INSERT Just before doing context.Posts.Add(item) do a query to all related items such as context.Blogs.Find(item.BlogId).
UPDATE When retrieving the Post, do it with .Include(d => d.Blog) + other related items.
DELETE When retrieving the Post, do it with .Include(d => d.Blog) + other related items.
An additional important thing that was causing me troubles is the layout of my Audit table. The issue was I reused the same property name in Audit table with a different type - in the original table the property Blog was a relationship property, whiles in the audit table it was a string. This caused errors in conversion from one to the other model.
[AuditInclude]
public class Post
{
...
[Required]
public int BlogId { get; set; }
public Blog Blog { get; set; }
...
}
Just rename it to something else like:
public class Audit_Post
{
...
public int BlogId { get; set; }
public string BlogName { get; set; }
...
}
...
// and in startup.cs use ...
...
.Map<Post, Audit_Post> ((d, al) => {
al.BlogName = d.Blog?.Name;
})
...
Regarding the 2nd issue - running audit inside transactions. I decided not to use it for now. I'll get covered the described case with tests.
Maybe a suggestion for future development of the package - it would be nice to have mentioned cases covered easily - I mean, transitive properties.

Answer 2

Your code should work fine if you Include the Blog property when retrieving the Post entity, for example:
using (var context = new BlogsContext())
{
var post = context.Posts
.Include(p => p.Blog) // Important, otherwise post.Blog will be NULL
.First();
post.Content += " adding this";
context.SaveChanges();
}
If you can't include the Blog entity because any reason, you could do the query on the mapping, but you will need to use a lower level overload on the Map method, like this:
.Map<Post, PostAudit>((ev, entry, postAudit) =>
{
var entryEf = entry.GetEntry();
var post = entryEf.Entity as Post;
var dbContext = entryEf.Context as BlogsContext;
// Get the blog related
var blog = dbContext.Blogs.FirstOrDefault(b => b.Id == post.BlogId);
postAudit.Blog = blog?.Name;
})
Regarding the other question, currently there is no built-in mechanism to rollback your database changes when the audit saving fails, but maybe you try with the AuditDbContext overrides