如何从 Entity Framework Core 中的导航集合属性中获取原始值？

Question

With Entity Framework Core, I need to check the original values of a navigation property inside my entity but i can't find a way to do it.

I'm able to read the original and the current values of the actual entity and also his reference property but the OriginalValue property is missing when I read the navigation property.

Here's what I been able to do so far.

var entries = ChangeTracker.Entries<Book>()
                .Where(x => x.State == EntityState.Modified)
                .ToList();

foreach (var entry in entries)
{   
   // read the entity current & original values 
   var currentTitleValue = entry.Property(x => x.Title).CurrentValue;
   var originalTitleValue = entry.Property(x => x.Title).OriginalValue;

   // read the reference object current & original values
   var promotionReferenceEntry = entry.Reference(x => x.Promotion);
   var currentPromotionPriceValue = promotionReferenceEntry.TargetEntry.Property(x => x.Price).CurrentValue;
   var originalPromotionPriceValue = promotionReferenceEntry.TargetEntry.Property(x => x.Price).OriginalValue;

   // read the navigation object current & original values
   var authorsCollectionEntry = entry.Collection(x => x.AuthorBooks);
   var currentAuthorIds = authorsCollectionEntry.CurrentValue.Select(x => x.AuthorId).ToList();
   var originalAuthorIds = ?????;
}

Answer 1

Here is a way to get the reference properties in the context as well as its original values:

var entries = ChangeTracker.Entries<Book>()
                .Where(x => x.State == EntityState.Modified)
                .ToList();

foreach (var entry in entries)
{
    // If it is Added/Deleted, you can't get the OriginalValues/CurrentValues respectively.
    // So make it Modified for the meanwhile.
    var tempState = entry.State;
    entry.State = EntityState.Modified;
    
    // Clone the Entity values (the original ID, Current ID of the navigation
    var currentValues = Entry(entry.Entity).CurrentValues.Clone();
    var originalValues = Entry(entry.Entity).OriginalValues.Clone();
    
    // Set the Entity values to the OriginalValues and load the reference
    Entry(entry.Entity).CurrentValues.SetValues(originalValues);
    Entry(entry.Entity).Reference(x => x.Promotion).Load();
    
    // Store the Original Reference value in a variable
    var promotionReferenceEntryOriginalValue = entry.Reference(x => x.Promotion).CurrentValue;
    
    // Set the Entity values back to CurrentValues and load the reference
    Entry(entry.Entity).CurrentValues.SetValues(currentValues);
    Entry(entry.Entity).Reference(x => x.Promotion).Load();
    
    // Store the Current Reference value in a variable
    var promotionReferenceEntryCurrentValue = entry.Reference(x => x.Promotion).CurrentValue;
    
    // Set the Entry State back to its original State Added/Modified/Deleted
    entry.State = tempState;
    
    // read the entity current & original values 
    var currentTitleValue = entry.Property(x => x.Title).CurrentValue;
    var originalTitleValue = entry.Property(x => x.Title).OriginalValue;

    // read the reference object current & original values
    //var promotionReferenceEntry = entry.Reference(x => x.Promotion);
    var currentPromotionPriceValue = promotionReferenceEntryCurrentValue.Price; // promotionReferenceEntry.TargetEntry.Property(x => x.Price).CurrentValue;
    var originalPromotionPriceValue = promotionReferenceEntryOriginalValue.Price; // promotionReferenceEntry.TargetEntry.Property(x => x.Price).OriginalValue;
}

To make it dynamic, remove the type <Book> from ChangeTracker.Entries<Book>() and loop though the entry.Entity properties inside the foreach (var entry in entries) loop:

foreach (var propertyInfo in entry.Entity.GetType().GetProperties())
{
    var propertyName = propertyInfo.Name;
    //Do the loads here...
    //Get the values
}

Check if it is a navigation reference or a collection reference by trying to access it using extra methods and check if it is null or not, not null means it is a valid property to try and load() it:

private DbPropertyEntry GetProperty(DbEntityEntry entry, string propertyName)
{
    try
    {
        return entry.Property(propertyName);
    }
    catch { return null; }
}

private DbReferenceEntry GetReference(DbEntityEntry entry, string propertyName)
{
    try
    {
        return entry.Reference(propertyName);
    }
    catch { return null; }
}

private DbCollectionEntry GetCollection(DbEntityEntry entry, string propertyName)
{
    try
    {
        return entry.Collection(propertyName);
    }
    catch { return null; }
}