BreezeJS Reconstruct SaveResult on Server in .NET - angularjs

Question

Instead of using Breeze server side to save JObject, I'm using a dummy contextprovider to extract the EntityMaps and then performing custom validations on each entity and saving them myself. If the save succeeds, how do I reconstruct the SaveResult object to return back to the client so that BreezeJS client knows about my changes?
Currently I'm returning the following SaveResult:
// Using example here (https://github.com/Breeze/breeze.js.samples/issues/33)
// to extract EntityMaps from JObject.
// The return result is a Dictionary<Type, EntityInfo>.
var entityMaps = SaveBundleToSaveMap.Convert(saveBundle);
// ... Code to save entities to DB
// SaveResult to be returned to the client.
return new SaveResult()
{
Entities = entityMaps.SelectMany(innerEi => innerEi.Value.Select(ie => ie.Entity)).ToList<object>(),
Errors = null,
KeyMappings = new List<KeyMapping>()
};
How do I construct the KeyMapping list for single primary keys? How do I construct the KeyMapping for composite keys?

Answer 1

After some trial and error, I found that the SaveResult.KeyMapping list contain only the old and new keys generated from inserted entities. This makes sense because the client has the key of updates and do not need to worry about deleted entities.
To construct the SaveResult.KeyMapping list, first need to set the EntityInfo.AutoGeneratedKey.TempValue of each insert entity to the key sent from the client side, save the entities to get the new keys, and then create KeyMapping list and return back to the client.
1.Loop the entityMaps and set the TempValue for each EntityInfo to the key/id sent from the client side.
// Extract out from loop to make it more readable.
Action<EntityInfo> processEntityInfo = (ei) =>
{
if (ei.EntityState == EntityState.Added && (ei.AutoGeneratedKey != null && ei.AutoGeneratedKey.AutoGeneratedKeyType == AutoGeneratedKeyType.Identity))
{
var entity = ei.Entity;
var tempValue = ei.AutoGeneratedKey.Property.GetValue(entity);
ei.AutoGeneratedKey.TempValue = tempValue;
}
};
entityMaps.ToList().ForEach(map => map.Value.ForEach(ei => processEntityInfo(ei)));
2.Save the entities by calling the the Context.SaveChanges() on the EntityFramework Context. This will generate keys for all the inserted entities.
3.Loop through the saved entities in the entity maps and construct and return the KeyMapping list.
return entityMaps.SelectMany(entityMap =>
entityMap.Value
.Where(entityInfo => entityInfo.EntityState == EntityState.Added && (entityInfo.AutoGeneratedKey != null && entityInfo.AutoGeneratedKey.AutoGeneratedKeyType == AutoGeneratedKeyType.Identity))
.Select(entityInfo => new KeyMapping
{
EntityTypeName = entityInfo.Entity.GetType().FullName,
RealValue = entityInfo.AutoGeneratedKey.Property.GetValue(entityInfo.Entity),
TempValue = entityInfo.AutoGeneratedKey.TempValue
}));