EF更新关系的子关系

Question

EF tracking confuses me. Here is a scenario that I am trying to achieve:

public class CentralPoint
{
   public Guid ID { get; set; }
   public virtual BIDatabase BIDatabase { get; set; }
}

public class BIDatabase
{
    public Guid ID { get; set; }
    public Guid CentralPointID { get; set; }
    public virtual CentralPoint CentralPoint { get; set; }
    public Guid ConnectionID { get; set; }
    public virtual Connection Connection { get; set; }
}

public class Connection
{
    public Guid ID { get; set; }
    public string Username { get; set; }
    public string Password { get; set; }
}

These are my entity models. I am having a one-one relationship between CentralPoint and BIDatabase entities, also a one-one relationship between BIDatabase and Connection entities. Obviously there is a separate table for each of these entities.

Inside the controller I am updating the BIDatabase property of the CentralPoint with a new instance

centralPoint.BIDatabase = biDatabase;

Here is the controller part:

public async Task<IActionResult> AddBIDatabaseAsync(Guid cpId, BIDatabase biDatabase)
    {
       // context is available through Dependency Injection (.net core)
        var centralPoint = _context.CentralPoint.Where(cp => cp.ID == cpId)
            .Include(cp => cp.BIDatabase)
            .ThenInclude(biDb => biDb.Connection)
            .FirstOrDefault();

        centralPoint.BIDatabase = biDatabase;
        await _context.SaveChangesAsync();

        // more code ...
    }

After this:

CentralPoint Table -> Remains Unchanged: Normal

BIDatabase Table -> Updated with new IDs: Normal

Connection Table -> // A new row is added instead of updating the old one

What I wanted is the connection entity to be updated and not added every time for the same database.

Answer 1

I think I see the issue.

When you replace centralPoint.BIDatabase = biDatabase; your new BIDatabase object probably doesnt have the Id linking it to Connection

Try mapping the fields you need onto the existing object instead of replacing it (or replace it, but map any Ids and existing fields that you want to be persisted through onto the new object first).

Answer 2

What code created this new biDatabase? Was it persisted to a dbContext prior to this method?

Your expectation around the BIDatabase and connection table is a bit suspicious. Given an existing CentralPoint /w BIDatabase /w Connection, if you "change" the CentralPoint's BIDatabase to a new one, the existing record is not updated, it is replaced. This means that the old record and it's associated connection would be removed, and a new BIDatabase /wa new Connection would be inserted. Assuming these entities are configured with DB generated keys:

Example: CentralPoint(id:1) -> BIDatabase(id:1) -> Connection(id:1)

Create new BIDatabase (id:x) with new Connection (id:x) then:

CentralPoint.BIDatabase = newBIDatabase

BIDatabase(id:1) & Connection(id:1) are marked for deletion. new BIDatabase & Connection will be persisted with new IDs when saved.

CentralPoint(id:1) -> BIDatabase(id:2) -> Connection(id:2)

If you want to replace the BIDatabase but keep the same connection ID/reference:

Create the new BIDatabase(id:x) /w Connection(id:x)

but before saving it to the context:

   var centralPoint = _context.CentralPoint.Where(cp => cp.ID == cpId)
        .Include(cp => cp.BIDatabase)
        .ThenInclude(biDb => biDb.Connection)
        .FirstOrDefault();

   biDatabase.Connection = (centralPoint?.BIDatabase?.Connection) ?? biDatabase.Connection;

    centralPoint.BIDatabase = biDatabase;
    await _context.SaveChangesAsync();

What that extra statement does is look to preserve an existing connection already on the existing CentralPoint.BIDatabase by copying the reference over to the new BIDatabase. If the existing BIDatabase didn't have a connection (or the existing CP didn't have a BIDatabase) then the new connection created would be used. Provided you haven't saved the new BIDatabase to a dbContext prior to this code, the "new" Connection (id:x) will never get inserted where an existing one is substituted.

Answer 3

There were a couple of mistakes I was doing. I am detailing them so it might be helpful to others.

First mistake (pointed out by @Steveland83)

centralPoint.BIDatabase = biDatabase;

Since the CentralPoint entity is being tracked by the context (DbContext) we cannot simply replace a property by another. We need to modify the property by copying values. So the following should be done instead

_context.Entry(centralPoint.BIDatabase).CurrentValues.SetVal‌​ues(biDatabase);

Second mistake With the fix above, I was expecting the context to track all property changes in the centralPoint.BIDatabase and update those as well by itself (In my case the Connection property eg. centralPoint.BIDatabase.Connection)

However unfortunately this does not happen for non primitive types. You have to tell the context explicitly which of the non-primitive properties changed. Here is the second fix

_context.Entry(centralPoint.BIDatabase).CurrentValues.SetVal‌​ues(biDatabase);

_context.Entry(centralPoint.BIDatabase.Connection).CurrentValues.SetVal‌​ues(biDatabase.Connection);

This Updates the BIDatabase and the Connection tables with the changes.